ITGE20100136A1 - METHOD AND DEVICE FOR THE ACQUISITION OF MRI IMAGES - Google Patents

Description

DESCRIPTION of the Industrial Invention entitled: "Method and device for the acquisition of MRI images"

TEXT OF THE DESCRIPTION

The present invention relates to a method and a device for acquiring MRI images, in particular for bodies under examination which are subject to voluntary and / or involuntary movement or are positioned in such a way that the body under examination must autonomously maintain a position stable.

Said method comprises the following steps: a calibration phase;

an excitation and acquisition phase, in which the body under examination is permeated by a static magnetic field, and in which excitation sequences are applied to the body under examination and magnetic resonance signals emitted by the body under examination are received;

a phase of image reconstruction in which said received magnetic resonance signals are processed for the generation of the images, the images being acquired along section planes or slices of the body under examination having a predetermined orientation with respect to the body under examination and called layers acquisition.

The present invention also relates to a device for acquiring MRI images, in particular for bodies under examination which may be subject to voluntary and / or involuntary movement or are positioned in such a way that the body under examination must autonomously maintain a stable position, which device includes:

means for generating a static magnetic field;

means of generating magnetic field gradients;

calibration means;

means for sending radio frequency excitation pulses;

means for receiving magnetic resonance signals emitted by the body under examination;

means for processing said magnetic resonance signals emitted by the body under examination for generating images from these magnetic resonance signals.

The methods and devices of the aforementioned type are known and widely used and find their criticalities on the one hand in the quality of the images generated, in particular as regards the resolution, the absence of artifacts, the contrast of the same and / or the ratio signal / noise, and on the other hand in the time necessary to carry out the acquisitions and therefore to obtain these images.

Sometimes in clinical practice it may be desirable to reduce examination time as much as possible.

For example, in spinal imaging, it may be advantageous to keep the patient in an upright position during the examination, especially to highlight typical pathologies of the vertebral discs or soft tissues in general that would be difficult to see with the patient lying down.

For the patient, however, especially in the presence of pathologies, maintaining an upright position can be very painful, and the reduction of examination times can be not only desirable for the patient's comfort but above all necessary precisely because of the impossibility. of the patient to maintain the same position. Even in the absence of pathologies and therefore of pain, the fact of having to maintain a stably position such as the upright one is not easy, if we consider that the term stable or fixed position must be interpreted from the point of view of the tolerances of movement foreseen for the 'MRI imaging. When there are pathologies that cause pain, maintaining a fixed position is even more difficult with the risk of having movements that can lead to artifacts, making it necessary to re-perform the diagnostic examination and therefore prolonging the patient's suffering.

A widely used method for the optimization of the acquisition is the study of the so-called excitation sequences, i.e. the nature and temporal arrangement of the excitation pulses sent into the body under examination, in relation to the reception of the magnetic resonance signals generated by the body under examination in response to arousal and in relation to the application of field gradients

The impulses are sent precisely in temporal "sequences", having such impulses different frequencies, intensities, durations and presenting such excitation sequences with different repetition times, as well as the application of gradients and reception of signals carried out in accordance with the sending such impulses.

For the reconstruction of the images, being the same basically two-dimensional arrays of pixels, as is well known, the excitation sequences must be repeated for the number of times necessary to obtain all the information necessary for the reconstruction of the image acquired in the acquisition layer , that is the number of times necessary to acquire the image in the phase encoding direction.

Since between one sequence and the next it is necessary to wait for a repetition time TR which is determined by the physics of the system and in which the acquisition machine is substantially unused, the times for generating the images are rather long.

A known and widely used method to reduce the acquisition time is the one known under the name of multilayer or multislice.

According to this method, the repetition time TR, instead of being left unused with consequent under-exploitation of the equipment and lengthening of the examination times, is exploited to acquire other layers of the body under examination, which layers include nuclei not yet subjected to the action. of excitement.

In practice, after sending an excitation sequence with a selective pulse at a frequency corresponding to a specific first acquisition layer, a new excitation sequence is immediately sent with a selective pulse at a frequency corresponding to a second acquisition layer, different from the first, ie having a position relative to the body under examination different from the first layer.

This procedure is performed for a maximum number of layers possible in the duration of TR which is given by the repetition time TR divided by the duration of each sequence or layer duration DS, after which it is possible to send a new sequence in the first acquisition layer and the whole procedure is reiterated from scratch.

This technique allows to obtain faster examination times since the images from several acquisition layers are acquired practically simultaneously or in very rapid succession.

The limit of the multi-slice technology is constituted by the fact that in order to obtain an acquisition efficiency of a certain level it is necessary to extend the repetition time TR to such an extent as to allow the acquisition of different layers. Ultimately, the overall duration of a multi-slice acquisition with reference to the availability of the image relating to only one of the acquired layers is equal to the time necessary for the acquisition of all the layers envisaged in the multi-slice sequence.

For over-glove applications such a solution is not optimal, especially when it is preferable to obtain an image of a single layer in a short time.

This could be desirable, for example, to be able to carry out evaluations and / or processing on this image before acquiring a new one, be it on a different acquisition layer or on the same acquisition layer, or in the aforementioned case of spinal pathologies, in which it may be advantageous to reduce the acquisition time of an image on each single acquisition layer and above all to make this acquisition independent from those performed on the other layers, ie without having to wait for the total time necessary for the acquisition of all the acquisition layers.

For these particular applications the known methods currently do not find satisfactory solutions in terms of acquisition speed and image quality and also an optimization of the time according to the multislice technique is not usable.

The present invention aims to overcome the aforementioned drawbacks of currently known methods with a method as described at the beginning, in which the excitation and acquisition phase and possibly also the reconstruction phase are carried out layer by layer in sequential mode. and the excitation sequences used are fast excitation sequences with short repetition time.

Such a method has the great advantage of allowing to quickly obtain one image at a time on each acquisition layer.

This is guaranteed thanks to the sequential mode, according to which the excitation sequences are sent one after the other in the same acquisition layer for the number of times necessary to acquire the image in the phase encoding direction, up to the final reconstruction. of the image in the expected layer, being the sequential mode combined with the use of excitation sequences with short repetition time TR, i.e. fast excitation sequences.

This allows to obtain the fast acquisition of an image on an acquisition layer before possibly carrying out the acquisition on a further acquisition layer.

The method object of the present invention finds interesting application in different fields and acquisition methods such as:

imaging of the spinal column in a loaded state, as mentioned, that is with the patient standing and therefore at risk of undergoing movements that can negatively affect the quality of the images, with the possibility of checking each image;

the creation of sequences of images acquired in consecutive moments, so-called "cine", useful above all in the imaging of joints during their movement, such as the knee during flexion or extension;

the investigation of the evolution over time of the state of perfusion of the anatomical districts under examination, with the creation of a relative dynamic curve.

It should be noted that the reduction of the acquisition times of MRI images is a contrasting need with that of having high quality images.

Not all sequences are suitable for use and the present invention is based on a choice of optimization of the compromise condition between reduction of acquisition times and quality of the acquired image. This optimization or this compromise cannot be immediately deduced from the characteristics of the known sequences which in the specific technical field are not actually used for the detection of images of the type to which the present invention refers and which has been discussed in greater detail above.

In a preferred embodiment the said fast excitation sequences with short repetition time are sequences of the Gradient echo family, in particular both Steady-State and so-called trueFISP and other or Echo-Planar sequences.

It is important, before subjecting the body under examination to the excitation sequences, to set the parameters of the acquisition machine to optimal values for the accuracy of the signal detection.

This procedure, known as calibration, can be carried out by setting the machine with setting means regulated by a user interface, or it can be performed automatically by adjustment means, which can use, for example, feedback systems or feedback to reach the values. optimal.

Calibration usually mainly involves frequency tuning and receiving gain tuning for quantization noise.

Frequency calibration is important in the case of permanent magents as the resonance frequency of the magnet depends on the temperature and therefore, prior to acquisition, it is necessary to perform a thermal check to identify the condition of the device.

On the other hand, the calibration of the receiving gains allows to control the amplitude of the received signal, which may depend for example on the thickness of the acquisition layer, to avoid saturating the reception channel.

In an executive example, the calibration phase is performed once for each acquisition layer.

In a further executive example, the calibration phase is performed only once for all the acquisition layers or part of the acquisition layers.

This allows you to optimize times by deciding from time to time whether to perform a single calibration phase for all the acquisition layers or whether to perform a calibration phase for each acquisition layer or whether to perform single calibration phases for different groups of acquisition layer. .

The exception to the execution of the calibration for each of the acquisition sequences does not generate significant problems for the quality of the acquired images and above all for the detection of pathologies, in particular when these sequences are repeated at short intervals of time from each other.

As regards this particular way of proceeding with a single calibration for several subsequent acquisitions, it is also possible to provide for a verification measurement of the temperature parameters and other relevant parameters for calibration after the last acquisition sequence envisaged. In this case, the data detected can be compared with those detected in the initial calibration step and it is possible to give an indication of the reliability of the result or, if necessary, to foresee corrections of the image data with respect to those acquired in the various sequences on the basis of a correction function that uses the values of the parameters measured for calibration in the initial calibration steps and those measured after the last acquisition sequence.

The invention also allows configuring different types of combinations of calibration steps, excitation and acquisition steps and image reconstruction steps.

In a first combination, the calibration phase, the excitation and acquisition phase and the image reconstruction phase are carried out in succession for each acquisition layer.

This allows you to have an image at the end of the acquisition of each single acquisition layer, with excellent reliability thanks to a calibration phase performed for each acquisition layer.

In a second combination, only one calibration phase is performed at the beginning, and the excitation and acquisition phase for each acquisition layer is immediately followed by an image reconstruction phase for the current acquisition layer.

The calibration phase is therefore performed only once before starting the first series of excitation sequences relating to the first acquisition layer and is not repeated before the beginning of each series of excitation sequences relating to the subsequent acquisition layers.

This allows you to combine the calibration phases in a single initial calibration phase to reduce the total examination time.

In a third combination, a single calibration phase is performed at the beginning, an intermediate excitation and acquisition phase for all the acquisition layers, and a final phase of reconstruction of all the images for all the acquisition layers.

According to this executive example, the calibration phase is carried out only at the beginning, and the data obtained during the excitation and acquisition phase from each series of excitation sequences are temporarily stored.

When the number of repetitions of the excitation sequences necessary for the reconstruction of the image on a first acquisition layer is reached, the sending of the excitation sequences to the next layer begins, without carrying out the reconstruction of the image.

Once all the data relating to the number of slices expected from the imaging session have been stored, the reconstruction of all the images is carried out on the basis of the stored data.

In a fourth combination, the calibration phase and the excitation and acquisition phase are performed for each acquisition layer, while a single final phase is envisaged for the reconstruction of all the images for all the acquisition layers, with the aforementioned modalities.

In a fifth combination, only one calibration phase is performed at the beginning, and the excitation and acquisition phase for each acquisition layer is immediately followed by an image reconstruction phase for the current acquisition layer.

The calibration phase is therefore performed only once before starting the first series of excitation sequences relating to the first acquisition layer and is not repeated before the beginning of each series of excitation sequences relating to the subsequent acquisition layers, while it is foreseen a phase of detection of the physical parameters necessary for the calibration after the acquisition of the image relating to the last expected layer and the determination of a correction function of the image data relating to the various layers based on a correction function that calculates these corrections based on the differences in the values of the physical parameters necessary for calibration measured in the initial calibration phase compared to the physical parameter values necessary for calibration measured at the end of the image acquisition of the last expected layer.

This makes it possible to combine the calibration phases in a single initial calibration phase for the reduction of the total examination time and to still have the possibility of correcting to a certain extent the images relating to the layers subsequent to the first that are acquired without a dedicated calibration phase is carried out for them.

A variant of this fifth combination provides that the images of the various layers are reconstructed at the end of all the acquisition sequences of all the layers.

In a further embodiment, the method object of the present invention provides for the following steps:

acquisition and generation of one or more initial scout images using fast excitation sequences in sequential mode on at least one predefined acquisition layer;

display of said one or more scout initial images;

definition on the basis of said one or more scout images of a predefined number of further layers to be acquired;

acquisition of each of the said layers to be acquired.

In this way it is possible for a user to make an evaluation of the first scout images acquired on acquisition plans of particular interest, and to decide on the basis of this evaluation if and which further layers to acquire and in what modality.

According to an executive example, the images of at least part of the acquisition layers are acquired in sequential mode and at least part in multilayer mode.

This makes it possible to advantageously choose between the two modes, for example according to the number and arrangement of the acquisition layers of interest.

It is also possible to provide the multilayer mode for the acquisition of several separate groups of acquisition layers.

In a further executive example, this method provides for the setting for the definition of the layers to be examined and / or the examination time and / or the quality of the images by a user, and an automatic processing for the definition and execution of a combination of calibration phases, excitation and acquisition phases with the choice of the relative excitation sequences, and image reconstruction phases in which said received magnetic resonance signals are processed for the generation of the image, which combination it is optimized for a reduction of the overall examination time.

In this way the user is relieved of the decision of the technical details of the acquisition, which are controlled internally by the device, but acts on them by setting the layers to be examined and / or the total time of the examination and / or the desired image quality. .

In addition, the method provides for optimizing the real time of acquisition duration during which the patient's immobility is required with times of execution of further steps, such as those of reconstruction or generation and display of images that allow the patient to relax and approximately maintain the acquisition position, without having to remain perfectly still. These are therefore the pause times provided between the individual time intervals in which the actual acquisition is performed and in which the patient must remain motionless and which pause times for the patient from the immobility condition are used for the execution of steps such as complete or partial processing of signals into image data.

The combined acquisition sequence therefore provides for dividing the overall duration into intervals of patient immobility and pause intervals and to predict immobility intervals equal to at least the duration of a single acquisition sequence and pause intervals equal to at least part of the duration. overall of the times required to process the resonance signals in image data and / or to display them.

According to an executive example, the body under examination is the area of the spinal column of a patient, who remains in an upright position for the entire duration of the acquisition.

The acquisition of images with the patient in an upright position allows to have the spine in a loaded condition and therefore to accurately evaluate any dysfunctions that would not be evident in an unloaded position.

In such a position it is difficult to ensure that the patient remains immobile for all the time necessary for the acquisition of the images and therefore the risk of artifacts and degradations deriving from the movement is high, and the present method guarantees a good solidity towards the movement. .

It is therefore possible, for example, to acquire one layer at a time by requiring the patient to remain motionless only for the time necessary for an acquisition, while it is possible for the patient to relax between the acquisition of one layer and that of the next layer.

In a further executive example, images are acquired from a single acquisition layer in consecutive instants, in such a way that the set of images generated contains information relating to the movement of the body under examination relative to the acquisition layer considered.

Such "cine" methodologies allow a visualization of the movement, and find an advantageous use in the analysis of the movement in the joints.

The sequential method associated with rapid sequences such as Gradient Echo or True Fisp or Echo Planar, allows you to quickly obtain images from a single acquisition layer, and therefore allows you to generate series of cine images with a high frame-rate, in order to better monitor changes in anatomical structures during movement.

According to a further example, images are acquired from a single acquisition layer in consecutive instants after administering a contrast medium to the patient, in such a way that a dynamic curve relating to the perfusion of the body under examination is generated relative to the acquisition layer considered. .

The administration step precedes the execution of the method step and does not form part of the protective scope to which the present invention is directed.

This application has substantially the same advantages described for cine sequences in joint motion imaging.

It is also possible to foresee that the images are acquired from a limited number of acquisition layers, rather than from a single acquisition layer, so that the analysis of the movement or of the perfusion trend is carried out on a greater number of acquisition layers, thus allowing the collection of a greater number of information, without on the other hand influencing too heavily on the advantages offered by the acquisition carried out on a single acquisition layer.

The order of magnitude of the number of layers depends on the specific cases and is about a few layers and for example less than a dozen layers.

The present method can be applied in the imaging of any anatomical district that is subject to an unstoppable and / or voluntary or involuntary movement, such as for example the arteries, the heart, the lungs, the intestine with peristalsis movements.

In these situations it may be advantageous to perform a single initial calibration phase to minimize the time required to acquire each image, thus lowering the risk of having motion artifacts.

In one embodiment, the image reconstruction phase is performed at the end of the reception of the magnetic resonance signals for each acquisition layer, thus generating an acquired image for each acquisition layer, the said acquired image being displayed, so such that an operator can view said acquired image and decide whether to store said acquired image and proceed with the acquisition of the next acquisition layer, or whether to delete said acquired image and carry out an acquisition again on the same layer.

This device allows an operator to have a real-time control of the images acquired in one acquisition layer at a time.

The great advantage of quickly obtaining an image on a certain acquisition layer is in this way profitably exploited to make merit assessments of the image quality, with the possibility of using it as a valid acquired image in the imaging session or discarding it if not meeting predefined quality criteria.

In a further embodiment, during the display of the image acquired in the current acquisition layer by the operator an acquisition of the next acquisition layer is performed and a new image is generated and this new image is temporarily stored by means of storage, in so that if the operator accepts the image currently displayed, the stored image is subsequently displayed, while if the operator rejects the image currently displayed, a new image is acquired in the current acquisition layer.

In the event that the operator rejects the image currently displayed, it is possible to foresee two alternative cases: in a first case the image currently displayed is deleted, in a second case the stored image is kept in memory, so that there is no need for a new acquisition performed in the next acquisition layer when viewing the newly acquired image in the current acquisition layer.

This makes it possible not to leave the machine unused for the time necessary for the control by the operator, but on the contrary to exploit this time to proceed with the acquisition of the image in the next acquisition layer.

In a further particularly advantageous embodiment, the user viewing and evaluation steps are replaced by automated processing and evaluation steps, since automatic means for processing and evaluating the acquired image are provided, which means generate an evaluation of the quality of the image. said acquired image and decide whether to store this acquired image and proceed with the scanning of the next acquisition layer, or whether to carry out an acquisition again in the current acquisition layer.

Such means can be automatic image analysis software, which software uses databases of clinical cases and reference parameters and compares the results obtained from the analysis of the images with these reference parameters, to generate an evaluation of correspondence of the image. the quality criteria defined by these reference parameters.

The present invention also relates to a device for acquiring MRI images as described at the beginning in which control means are further provided for setting said means for sending radio frequency excitation pulses, of said generation means. of magnetic field gradients and of the said means for receiving magnetic resonance signals emitted by the body under examination upon the execution of an excitation and acquisition, and / or of an image reconstruction, performed layer by layer in sequential mode, and the excitation sequences used are fast excitation sequences with short repetition time.

According to an executive example, the said fast excitation sequences with short repetition time are sequences of the Gradient Echo type, in particular Echo-Planar or Steady-State so-called trueFISP.

In a further embodiment, the said control means allow the definition of the layers to be examined and / or the examination time and / or the quality of the images by a user, automatic processing means being provided for the definition and execution of a combination of calibration steps carried out by said calibration means, excitation and acquisition phases with the choice of the relative excitation sequences carried out by said means for sending radio frequency excitation pulses and by said means for receiving magnetic resonance signals emitted by the body under examination, and phases of reconstruction of the acquired image carried out by said processing means of said magnetic resonance signals emitted by the body under examination for the generation of images, which combination is optimized for a reduction in the overall examination time .

According to a further embodiment, the processing means of the said magnetic resonance signals emitted by the body under examination for the generation of images perform a reconstruction of the image at the end of the reception of the magnetic resonance signals for each acquisition layer, thus generating for each acquisition layer an acquired image, means for displaying said acquired image being also provided, in such a way that an operator can view said acquired image and decide whether to store said acquired image and proceed to scan the next acquisition layer , or whether to delete that scanned image and scan the same layer again.

According to a further improvement, automatic means for processing and evaluating the quality of the acquired image are provided, which means generate an evaluation of the quality of said acquired image and decide whether to store said acquired image and proceed with the scanning of the next acquisition layer, or whether to carry out again an acquisition in the current acquisition layer.

It should be emphasized that the method according to the present invention and in the forms indicated above and described in detail and claimed hereinafter can be envisaged not only for so-called 2D sequences, but also for three-dimensional acquisition sequences.

These and other characteristics and advantages of the present invention will become clearer from the following description of some executive examples illustrated in the attached drawings in which:

fig. 1 illustrates the multilayer or multislice method of using the excitation sequences forming part of the state of the art;

fig. 2 illustrates the sequential method of using the excitation sequences;

figs. 3, 4, 5 and 6 illustrate three executive examples of the use of the excitation sequences according to the present invention;

fig. 7 schematically illustrates the structure of the device object of the present invention; figs. 8, 9 and 10 illustrate three executive examples of acquisition and control modes of the images acquired according to the present invention.

Figure 11 illustrates with reference to the example of Figure 8 the relationship between the steps of acquisition, calibration, generation and display of the image and the periods of pause from the immobility condition and maintenance of the immobility condition of a patient undergoing imaging. with the protocol according to the present invention.

Figure 1 illustrates the multilayer or multislice mode of use of the excitation sequences, widely used to reduce the acquisition time as already described above.

The multislice mode provides for the sending of a first sequence 1 relating to a first acquisition layer, which is characterized by a time DS or layer duration, and a repetition time TR.

To prevent the acquisition machine from remaining unused during the repetition time, at the end of the time DS a second sequence 2 relating to a second acquisition layer is sent. This can be done by changing the frequency of the selective pulse.

It is possible to send further sequences 3, 4, 5 in further acquisition layers as long as the sum of all the times DS remains lower than TR, after which it is possible to send again the first sequence 1 relative to the first acquisition layer.

The relationship between the time DS and the time TR therefore defines the maximum number of layers that can be acquired at the same time.

Figure 2 illustrates the sequential method of using the excitation sequences, in which the sequence 1 is sent on the same acquisition layer for all the times necessary for the acquisition of the image in the direction of phase encoding.

The sequential method therefore allows to obtain the image relative to an acquisition layer before acquiring images in further acquisition layers.

This is especially relevant when, as schematically represented in the figure, the time DS and the time TR tend to have the same duration, i.e. when TR is drastically reduced, as in the case of the Gradient Echo sequences.

The sequences used can be in particular Echo-Planar or Steady-State so-called trueFISP.

Figure 3 illustrates a first executive example in which the following is carried out for each acquisition layer:

a system calibration step 6, ie setting the optimal values of the acquisition parameters of the machine, to optimize accuracy;

an excitation and acquisition phase which involves 1 <1> sending a first series of excitation sequences 1, with the relative applications of gradients and signal readings, using the sequential method, for the number of times necessary to acquire the image;

a phase of reconstruction of the first image 8 acquired in the first acquisition layer.

Once 1 <1> image 8 has been obtained, the procedure is repeated on a second acquisition layer with a calibration phase 6, a series of excitation sequences 2, until the second image 9 is obtained, then on a third acquisition layer until a third image 10 is obtained and so on up to the nth layer in which the nth sequence 7 will be sent to obtain the nth image 11, so that the images are acquired in all the acquisition layers necessary for the imaging session.

Figure 4 illustrates a further executive example according to which calibration 6 is performed only once before starting the first excitation and acquisition phase with the first series of excitation sequences 1 relative to the first acquisition layer and is not repeated before beginning of each series of excitation sequences 2, 3, ..., 7 relative to the subsequent acquisition layers.

In a further executive example illustrated in Figure 5, the calibration phase 6 is again carried out only at the beginning, and furthermore the data obtained from each series of excitation sequences 1, 2, 3, 7 are temporarily stored, so that when the number of repetitions of the excitation sequences necessary for the reconstruction of the image is reached, the sending of the excitation sequences into the next acquisition layer begins, without carrying out the reconstruction of the image.

Once all the data relating to all the n layers foreseen by the imaging session have been stored, the reconstruction of all the images 8, 9, 10, ..., 11 is carried out.

Figure 6 illustrates a further example in which the calibration step 6 is performed for each acquisition layer before the excitation and acquisition step on the same acquisition layer, as illustrated in Figure 3, while a single final reconstruction step is provided. as described for figure 5.

Figure 7 schematically illustrates the structure of the device object of the present invention in which a central computing unit or CPU 28 is provided, which CPU 28 is connected to input user interface means 27 and to output user interface means.

The input user interface 27 may comprise any setting and command means such as a keyboard, and the output user interface may comprise a screen 34 for displaying images, which may in turn be a touch screen. screen and be included in the input user interface unit 27.

The CPU 28 controls the means for generating magnetic field gradients 29, the calibration means 33, the means for sending radiofrequency excitation pulses 30, the means for receiving magnetic resonance signals emitted by the body under examination 31, means for processing said magnetic resonance signals emitted by the body under examination for the generation of images 32, indicated for clarity as components of an image acquisition unit 35.

The CPU 28 is also connected to a memory unit 26, which memory unit 26 can in turn contain memory sub-units containing data or calculation programs that can be managed by the CPU 28.

This memory unit 26 can for example comprise a temporary memory unit 264 in which the received signals and the reconstructed images are temporarily recorded.

According to an executive example, one or more scout images are initially acquired by means of said acquisition unit 35, for example in the central acquisition layers of the intervertebral discs of interest.

It is also possible, prior to the acquisition of these scout images, the acquisition of a panoramic image that allows the user to have general information on the body under examination, as is normally the case in a clinical setting.

Once the scout images have been acquired, they are displayed on the screen 34, so that they can be evaluated by the user.

The evaluation of the images in general, and in particular of the scout images, can also be done by a quality evaluation program 261, as explained in more detail below, which compares the acquired images with a database of clinical cases 260.

It is also possible to provide a control program 262 for setting the acquisition modes, through which the user can specify which acquisition layers are of interest and, if necessary, what is the maximum time allowed for the diagnostic operation and which is the desired image quality.

In the aforementioned case relating to the intervertebral discs, the user can, for example, decide to select n further acquisition layers for each intervertebral disc.

In this phase the control program 262 can present some options to the user for the acquisition of the acquisition layers of interest, with an estimate of the time required.

The options can be for example an acquisition of all acquisition layers in a single multislice mode, or an acquisition of each acquisition layer in sequential mode, in combination with different types of excitation sequences, etc.

Once the control program 262 has received the choices made by the user as input, a time optimization program 263 is launched, which calculates the acquisition mode that meets the user's requirements in the shortest possible time. acquisition including calibration phases, excitation and acquisition phases, reconstruction phases, evaluation by the user or by automatic means, use of certain excitation sequences, use of multilayer and / or sequential modes.

Figure 8 illustrates an operating diagram of an executive example of the method object of the present invention, in particular in relation to imaging of the spinal column for patients in an upright or substantially upright position.

The method provides an image acquisition and generation step 14, in which the image is acquired on a first acquisition layer, and a subsequent display 15 of this image.

Any type of user interface such as a keyboard monitor or a touch screen can be used to view the image.

Subsequently, an image evaluation step by the user or operator 16 is provided, in which, through said user interface, the operator inputs an evaluation of the image quality to predetermined management software 262.

This evaluation can be, for example, a simple acceptance / non-acceptance of the image or alternatively a series of numerical values included in reference scales, calculation algorithms being provided to reduce these values to a simple acceptance / non-acceptance of the image.

If the user's evaluation is positive, one proceeds with a memorization of the image 17 and with the acquisition of an image in the subsequent acquisition layer 18, and then the whole procedure is repeated from the beginning with the new image.

If, on the contrary, the user's evaluation is negative, the image is discarded and a new image is acquired in the same acquisition layer.

Figure 9 illustrates a variant of the executive example of Figure 8, in which the display of the image 15 and the evaluation of the image by the user 16 are replaced with an image processing 20 and an automatic evaluation of the image 21.

To carry out this processing and for this automatic evaluation, specific processing and automatic image analysis software 261 are provided, which can use processing methods such as contrast increase, noise filtering, edge detection, segmentation and automatic recognition of anatomical structures. notes, or the like.

Such software uses databases of clinical cases 260 and of reference parameters and compares the results obtained from the analysis of the images with these reference parameters, to generate an evaluation of correspondence of the image to the quality criteria defined by these reference parameters.

Figure 10 illustrates a further improvement, according to which, simultaneously with the display / processing of the image 22, an acquisition and generation step of the image is carried out in the subsequent acquisition layer 23 and a momentary storage 24 of the same in a temporary memory unit 264.

In this way, if the operator accepts the image currently displayed, the stored image is subsequently displayed by loading the image of the subsequent acquisition layer 25, while if the operator rejects the image currently displayed, a new image is acquired. in the current acquisition layer.

In the event that the operator rejects the image currently displayed, it is possible to foresee two alternative cases: in the particular case illustrated in the figure, the image currently displayed is deleted, but it is also possible to foresee that the stored image is kept in the temporary memory 264, in such a way that a new acquisition performed in the next acquisition layer is not necessary during the display of the newly acquired image in the current acquisition layer.

Figure 11 illustrates with reference to the example of Figure 8 the relationship between the steps of acquisition, calibration, generation and display of the image and the periods of pause from the condition of immobility and maintenance of the immobility condition of a patient undergoing imaging. with the protocol according to the present invention.

In this case, the calibration step identified with 30 has been introduced and the dashed arrows indicate that it is possible to perform a single calibration step for a plurality of subsequent acquisitions or the calibration step can be performed for each acquisition relating to each of the layers. along which you want to get an image.

With 31 and 32 were identified the intervals of pause from the condition of immobility with respect to the intervals in which the patient must remain immobile.

As is clear, the duration of the immobility condition is very short compared to the time necessary for the execution of all the steps. This allows the patient to relax and prepare for a new very short interval of immobility if necessary. Using the sequences suggested above it is possible that the duration of each layer acquisition is very short and very similar to that required for a traditional X-ray image.

The previous detailed description has used only two-dimensional acquisition sequences for descriptive simplicity. However, the invention also applies to three-dimensional acquisition sequences, that is, suitable for acquiring image data relating to a predetermined volume inside the body under examination. Therefore also this embodiment of the method is part of the present invention and falls within the protective scope of the same.

Furthermore, any step of a surgical or invasive type on the human body is to be considered not forming part of the present invention, but is a step either prior to or subsequent to the claimed method which refers to a mode of control and operation of MRI machines.

Claims (19)

CLAIMS 1. Method of acquiring MRI images, in particular for bodies under examination that are subject to voluntary and / or involuntary movement or are positioned in such a way that the body under examination must autonomously maintain a stable position, which method provides for the following steps: a calibration phase; an excitation and acquisition phase, in which the body under examination is permeated by a static magnetic field, and in which excitation sequences are applied to the body under examination and magnetic resonance signals emitted by the body under examination are received; a phase of image reconstruction in which said received magnetic resonance signals are processed for the generation of the images, the images being acquired along section planes or slices of the body under examination having a predetermined orientation with respect to the body under examination and called layers acquisition; characterized by the fact that the excitation and acquisition phase and possibly also the reconstruction phase are carried out layer by layer in sequential mode and the excitation sequences used are fast excitation sequences with a short repetition time. 2. Method for acquiring MRI images according to claim 1, characterized in that said fast excitation sequences with short repetition time are sequences of the Gradient Echo type, in particular Echo-Planar or Steady-State so-called trueFISP. 3. Method for acquiring MRI images according to one or more of the preceding claims, characterized in that the calibration step is performed once for each acquisition layer. 4. Method of acquiring MRI images according to one or more of the preceding claims, characterized in that the calibration step is performed only once for all the acquisition layers or part of the acquisition layers. 5. Method for acquiring MRI images according to one or more of the preceding claims, characterized in that it involves the following steps: acquisition and generation of one or more scout initial images using fast excitation sequences in sequential mode on at least one predefined acquisition layer; display of said one or more scout initial images; definition on the basis of said one or more scout images of a predefined number of further layers to be acquired; acquisition of each of the said layers to be acquired. 6. Method for acquiring MRI images according to one or more of the preceding claims, characterized in that the images of at least part of the acquisition layers are acquired in sequential mode and at least part in multilayer mode. 7. Method of acquiring MRI images according to one or more of the preceding claims, characterized in that it provides for the setting for the definition of the layers to be examined and / or the examination time and / or the quality of the images by a user , and an automatic processing for the definition and execution of a combination of calibration phases, excitation and acquisition phases with the choice of the relative excitation sequences, and image reconstruction phases in which said magnetic resonance signals received are processed for the generation of the image, which combination is optimized for a reduction of the overall examination time. 8. Method for acquiring MRI images according to one or more of the preceding claims, characterized in that the body under examination is the area of the spinal column of a patient, who remains in an upright position for the entire duration of the acquisition. 9. Method of acquiring MRI images according to one or more of the preceding claims, characterized in that images are acquired from a single acquisition layer in consecutive instants, in such a way that the set of images generated contains information relating to the movement of the body under examination in relation to the acquisition layer considered. 10. MRI image acquisition method according to one or more of the preceding claims, characterized in that images are acquired from a single acquisition layer in consecutive instants, in such a way that a dynamic curve relative to the perfusion of the body under examination is generated relative to the acquisition layer considered. 11. MRI image acquisition method according to claim 9 or 10, characterized in that the images are acquired from a limited number of acquisition layers, preferably less than 5. 12. Method of acquiring MRI images according to one or more of the preceding claims, characterized in that the image reconstruction step is performed at the end of the reception of the magnetic resonance signals for each acquisition layer, thus generating for each acquisition layer an acquired image, the said acquired image being displayed, in such a way that an operator can view the said acquired image and decide whether to store this acquired image and proceed to scan the next acquisition layer, or whether to delete this image scanned and scan the same layer again. 13. MRI image acquisition method according to claim 12, characterized in that, during the display of the acquired image in the current acquisition layer for control by said operator, a scan of the next acquisition layer is performed and generated a new image and this new image is temporarily stored by means of storage, so that if the operator accepts the currently displayed image, the said stored image is subsequently displayed, while if the operator rejects the currently displayed image a new image is acquired in the current acquisition layer. 14. Method of acquiring MRI images according to one or more of the preceding claims, characterized in that the user viewing and evaluation steps are replaced by automated processing and evaluation steps, automatic processing and evaluation means being provided of the quality of the acquired image, which means generate an evaluation of the quality of said acquired image and decide whether to store said acquired image and proceed with the scanning of the next acquisition layer, or whether to carry out an acquisition again in the current acquisition layer. 15. Device for the acquisition of MRI images, in particular for bodies under examination that may be subject to voluntary and / or involuntary movement or are positioned in such a way that the body under examination must autonomously maintain a stable position, which device comprehends : means for generating a static magnetic field; means for generating magnetic field gradients (29); calibration means (33); means for sending radio frequency excitation pulses (30); means for receiving magnetic resonance signals emitted by the body under examination (31); means for processing said magnetic resonance signals emitted by the body under examination for generating images (32); characterized by the fact that control means are provided for setting said means for sending radio frequency excitation pulses (30), said means for generating magnetic field gradients (29) and said means for receiving magnetic resonance signals emitted by the body under examination (31) to the execution of an excitation and acquisition, and / or of an image reconstruction, performed layer by layer in sequential mode, and the excitation sequences used are fast excitation sequences with short repetition time. 16. Device for the acquisition of MRI images according to claim 15, characterized in that the said fast excitation sequences with short repetition time are sequences of the Gradient Echo type, in particular Echo-Planar or Steady-State so-called trueFISP. 17. Device for the acquisition of MRI images according to one or both of claims 15 or 16, characterized in that said control means allow the definition of the layers to be examined and / or the examination time and / or the quality of the images by a user, automatic processing means (263) being provided for the definition and execution of a combination of calibration steps performed by said calibration means (33), excitation and acquisition steps with the choice of the relative sequences of excitation carried out by the said means for sending out radio frequency excitation pulses (30) and by the said means for receiving magnetic resonance signals emitted by the body under examination (31), and phases of reconstruction of the acquired image carried out by said means of processing of said magnetic resonance signals emitted by the body under examination for the generation of images (32), which combination is optimized for a reduction of the overall time d i exam. 18. Device for the acquisition of MRI images according to one or more of claims 15 to 17, characterized in that the means for processing said magnetic resonance signals emitted by the body under examination for the generation of images (32) perform a reconstruction of the image at the end of the reception of the magnetic resonance signals for each acquisition layer, thus generating an acquired image for each acquisition layer, also being provided means for displaying said acquired image (34), so that an operator can view said acquired image and decide whether to store said acquired image and proceed with scanning the next acquisition layer, or whether to delete said acquired image and perform a scan on the same layer again. 19. Device for the acquisition of MRI images according to one or more of claims 15 to 17, characterized in that automatic means for processing and evaluating the quality of the acquired image (261) are provided, which means generate an evaluation of the quality of the said acquired image and decide whether to store this acquired image and proceed with the scanning of the next acquisition layer, or whether to carry out an acquisition again in the current acquisition layer.