JP2004503269A - Magnetic resonance imaging system using stepping table - Google Patents

Abstract

Magnetic resonance imaging methods include capturing a data set of magnetic resonance signals from each scan volume of the subject. Capturing the data set is initiated based on the adjustment signal. Prescan is used to obtain the adjustment signal. Desirably, a fluoroscopic scan of the thick slice is used to determine the appropriate point in time to begin capturing the data set. This acquisition may be initiated manually while viewing a thick slice fluoroscopic MR image. Alternatively, acquisition of the data set may be automatically initiated based on a comparison of the adjustment signal to a preselected criterion.

Description

[0001]
The present invention relates to a magnetic resonance imaging method for capturing a data set of magnetic resonance signals from each scan volume of a subject.
[0002]
Such a magnetic resonance imaging method and a corresponding magnetic resonance imaging system are known from US Pat. No. 5,928,148.
[0003]
Known magnetic resonance imaging methods relate in particular to MR angiography, which produces magnetic resonance images of the vasculature of a patient. In particular, a contrast agent is administered to improve the contrast of the patient's arteries. According to known magnetic resonance imaging methods, magnetic resonance signals are captured from a large region of interest by translating the patient to successive positions where each set of magnetic resonance signals is to be picked up. To this end, the receiver system of known magnetic resonance imaging systems includes a fixed local receiver coil that is directed adjacent to the patient to capture magnetic resonance signals. In another embodiment of the known magnetic resonance imaging system, the receiver system includes a multi-segment local coil movable with the patient, the coil segments being sequentially switched to an active state. In successive positions, each part of the patient to be examined is moved into the field of view of the magnetic resonance imaging system. Each scan volume is defined by a respective part of the patient, and a respective coil segment captures magnetic resonance signals from each part at successive locations. According to known magnetic resonance imaging methods, each scan volume is aligned so that sets of magnetic resonance signals can be concatenated to form a single MR image of the entire region of interest.
[0004]
In MR angiography, a contrast agent is injected into one of the patient's veins, reaches the patient's heart, and is delivered from the heart as a contrast agent to the patient's vasculature. In order to image the patient's vasculature while being properly filled with the contrast agent, known methods use another "timing" scan that measures the speed of the contrast agent. The time elapsed from injecting the contrast agent into the vein until the contrast agent reaches the relevant artery is estimated from the measured speed. Patient movement between successive positions is controlled based on this estimated time course.
[0005]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic resonance imaging method which makes it possible to easily capture a magnetic resonance signal together with administration of a contrast agent. It is a further object of the present invention to provide a magnetic resonance imaging method for generating diagnostically high quality magnetic resonance images of a patient's arterial vasculature.
[0006]
This object, according to the invention,
Using a preliminary scan to capture a preliminary magnetic resonance signal from the subject;
Generating an adjustment signal based on the pre-scan;
Capturing a data set of magnetic resonance signals from each scan volume of the subject;
Capturing the data set is accomplished by a magnetic resonance imaging method, initiated based on the adjustment signal.
[0007]
According to the present invention, a first preliminary magnetic resonance scan is performed. The presence of a contrast agent is detected from the magnetic resonance signals picked up in the preliminary magnetic resonance scan. This is done after the contrast agent has been injected into the vein of the patient to be examined. For example, a preliminary magnetic resonance scan produces a fluoroscopic magnetic resonance image of a relatively thick slice with a relatively wide field of view. An adjustment signal is formed based on the detected contrast. Acquisition of the data set is initiated based on the adjustment signal. For example, the contrast may be detected by an operator and then the adjustment signal manually generated, for example, by the operator pressing a button or issuing a software command to the magnetic resonance system. The operator may use various properties of the contrast to determine about the generation of the adjustment signal that will begin capturing the data set. The operator can determine the start of the contrast or the rate of increase of the contrast in the specific region, based on the strength of the contrast. Such contrast properties are manifested in the magnetic resonance signal from the pre-scan. The beginning of the contrast is derived from the fluoroscopic magnetic resonance signal, for example, the arrival of the contrast to the patient's abdominal artery and / or iliac bifurcation is detected. To this end, the preliminary magnetic resonance signal is reconstructed from the magnetic resonance signals from the preliminary scan. This preliminary magnetic resonance image is displayed to the operator.
[0008]
Capture of the data set may be automatically initiated. For this purpose, the adjustment signal is derived from the prescan so that the signal level of the adjustment signal represents the temporal change of the contrast in the object. This adjustment signal may be derived from a magnetic resonance signal from a preliminary scan or from a reconstructed preliminary magnetic resonance image, such as a fluoroscopic magnetic resonance image. Automatic initiation of data set capture is typically based on a comparison of the adjustment signal to a preselected criterion.
[0009]
The preselected criterion represents the onset of contrast when the contrast agent is injected. The pre-selected criteria may be set by the operator before each MR examination or may have standard values. The optimal value for the preselected contrast is obtained empirically, for example by clinical trials with healthy individuals.
[0010]
If the comparison of the control signal with the preselected contrast shows that the contrast is sufficient, the prescan is stopped and the acquisition of the magnetic resonance signal data set is started. The data set contains, in particular, magnetic resonance signals relating to the three-dimensional volume of the patient to be examined. For example, magnetic resonance signals are acquired from one or more scan volumes, and the magnetic resonance signals include a number of relatively thin slices in the scan volume. Further, the magnetic resonance signal data set is preferably acquired by scanning the k-space in a manner that prevents vein enhancement in the magnetic resonance signal data set. For example, k-space is scanned linearly in time through the center of k-space, or k-space is scanned from the center of k-space toward the outer surface of k-space.
[0011]
From the magnetic resonance signal data set, one or more magnetic resonance images of the patient to be examined are reconstructed. These images show the patient's arterial system at high resolution, where small details with low contrast are better visible.
[0012]
It is advantageous to automatically switch from pre-scan to capture. Therefore, this switching does not require the attention of the person scanning the magnetic resonance system. Thus, the person scanning the magnetic resonance system can give more attention to the patient to be examined. In addition, the timing for initiating data set capture is more accurate than manually switching from pre-scan to data set capture.
[0013]
The above and other aspects of the invention will be better understood with the preferred embodiments as defined in the dependent claims.
[0014]
Desirably, a set of masks of the magnetic resonance signals are captured before the contrast agent is administered. Each mask set is associated with a separate spatial scan volume of the patient to be examined. To capture these separate sets of masks, the patient is moved between successive positions, and at each position the relevant scanning volume is placed at the isocenter of the magnetic resonance imaging system. According to the invention, capturing the mask set involves moving the patient along successive positions in mask order. Similarly, to capture these separate data sets, the patient is moved between successive positions, and at each position the scan volume is placed at the isocenter of the magnetic resonance system. According to the invention, capturing the mask set involves moving the patient along successively lower positions in the order of the data. Since the order of the data and the order of the masks are in opposite directions, the patient to be examined only needs to be moved back and forth once, and without the acquisition of magnetic resonance signals between the positions, the patient may be moved between positions. Will not be moved. Thus, the patient is prevented from becoming motion sick, and the procedure of moving the patient from one position to the next to capture the mask set and data set is less cumbersome. Desirably, the mask sets are captured in order from the patient's feet to the patient's abdomen, and the data sets are captured from the patient's abdomen to the patient's feet. In this way, the patient is first positioned with the abdomen near the isocenter of the magnetic resonance imaging system, so that scanning of the abdominal region is started after the preliminary scan has signaled sufficient contrast. When sufficient contrast is signaled, the patient's abdominal region is at the isocenter of the magnetic resonance imaging system and no further movement of the patient is required.
[0015]
Advantageously, the mask set and the data set are used to compare changes that have occurred in the time elapsed between the acquisition of the mask set used as a reference and the acquisition of the data set. Desirably, the contrast agent is administered between the capture of the mask set and the data set. Magnetic resonance images are reconstructed from individual mask sets. Contrast magnetic resonance images are reconstructed from individual data sets. By subtracting the mask magnetic resonance image from the corresponding contrast magnetic resonance image associated with each position, a differential magnetic resonance image is formed. These difference images mainly represent the patient's vasculature and further represent the patient's arterial system.
[0016]
The mask set may be captured after capturing the data set. In this case, the acquisition of the mask set must be started after the contrast agent that would have been used for the acquisition of the data set has disappeared from the area to be imaged.
[0017]
The feature that the order of the data and the order of the masks are reversed can be advantageously used independently of the pre-scan for generating the adjustment signal. On the one hand, pre-scanning and the reversal of data order and mask order are technically relevant in that they aim to move the patient to be examined efficiently between different positions. Both features contribute in particular to the acquisition of a data set of the respective scan volume, corresponding to the presence or arrival of a contrast agent in the relevant scan volume.
[0018]
The present invention also relates to a magnetic resonance imaging system. In general, in order to generate and capture magnetic resonance signals, a number of settings for the magnetic resonance imaging system need to be determined. Such settings are particularly determined while the patient is located in the examination zone of the magnetic resonance imaging system. The settings of the magnetic resonance imaging system can thus be precisely adapted to the actual patient to be examined. Such settings include, for example, tuning or matching the RF coil to the patient to be examined, RF power optimization, the Larmor frequency or center carrier frequency of the modulated magnetic resonance signal (f ₀ ), Automatic shimming, receiver optimization, receiver correction and / or echo phase determination. Preferably, each set of settings is implemented for a respective scan volume, ie, a respective position. According to the invention, these settings are realized in a preparation sequence before the mask set is captured and a pre-scan is performed and the data set is captured. It can be seen that the settings obtained from the preparation sequence are also suitable for accurate acquisition and pre-scanning of mask sets and data sets. In this way, unnecessary repetition of the preparation sequence for achieving the setting is avoided. Thus, the magnetic resonance imaging system according to the present invention requires only a relatively short time to generate and capture signals.
[0019]
Preferably, the magnetic resonance imaging system is provided with a patient carrier, for example a patient table, on which the patient is mounted and arranged in the examination zone of the magnetic resonance imaging system. An examination zone is an area in a magnetic resonance imaging system where magnetic resonance signals can be generated when an object is placed therein and from which magnetic resonance signals can be captured. The magnetic resonance signal is generated, for example, by an RF excitation coil. The magnetic resonance signal is picked up by an RF antenna such as an RF coil. Often used for both excitation and acquisition of magnetic resonance signals. During the generation and / or acquisition of a magnetic resonance signal, a temporary gradient magnetic field is applied, usually by activating a gradient coil. The examination zone is formed by an area accessible to excitation by an RF excitation coil and where the RF antenna has substantial sensitivity to magnetic resonance signals.
[0020]
According to the invention, the patient table comprises several platforms. Such a cradle is used to locally support the patient's leg so as not to limit the movement of the patient's leg muscles. This is achieved in particular by supporting the indentation of the patient's knee on the first gantry and supporting the patient's ankle on the second gantry. In this way, the patient's leg is firmly fixed, especially without restricting the movement of the calf and thigh muscles. Unrestricted muscle movement prevents disruption of blood flow, particularly blood transfer from arteries to veins through the capillary system. Thus, the arrival of the blood containing the contrast agent into the vein is delayed, and enhancement of the vein in the magnetic resonance signal of the data set is avoided. The cradle may be formed as an actual trestle carrying the cross bar at the fork, but for example a hard, elongated cushion may be used. Advantageously, the bars are convex on the top and have a width of about 10 to 15 cm. Such a convex, relatively wide bar supports the patient's leg without pinching the blood vessels. In this way, vein enhancement is delayed while the patient to be examined is comfortable.
[0021]
When the patient is moved into the examination zone, often the cables and / or tubes are moved with the patient into the examination zone. These cables and / or tubes are supported by supports having an L-shaped cross section. Thus, the support has two, for example, flat arms extending at an angle to one another. Preferably, the angle between the arms ranges from 50 ° to 130 °. The arms desirably extend perpendicular to each other. One arm of the support is located below the patient to be examined so that the support is firmly secured, the other arm extends laterally on the top of the patient supporting platform, and the cables and tubes are inspected. Prevent falling on patients to be done.
[0022]
Alternatively, the cables and / or tubes may be supported by a vertical bar secured to the table adjacent the patient and having a fixation point to join the cables and / or tubes.
[0023]
The cables and / or tubes are thus not pinched between the patient table and the gantry of the magnetic resonance imaging system surrounding the examination zone.
[0024]
Another preferred embodiment of the magnetic resonance imaging system of the present invention comprises an observation unit for measuring the position of the patient table at each scan position, for example corresponding to a scan volume or position. Such an observation unit is implemented, for example, as an electric potentiometer system providing an electric position signal. The position measured at that position is compared with a reference value by a comparator. The reference position is stored in a memory, for example, a working memory of a control system of the magnetic resonance imaging system. The memory and the observation unit are coupled to the input port of the comparator, the output of the comparator providing a difference signal representing the deviation between the measured position and the reference position. The reference position represents, in particular, the intended position for the position in question, ie the intended position for the scanning volume in question. Thus, the comparator compares the actual position of the patient table with the intended position. The comparator applies the difference signal to a control system of the magnetic resonance imaging system. The control system adjusts the temporary gradient magnetic field and / or RF excitation based on the difference signal to adjust the effective scan volume so that the effective scan volume accurately corresponds to the reference position. Further, by applying the reconstruction of the magnetic resonance image from the magnetic resonance signal, it is possible to correct the deviation between the reference position and the actual position of the patient table. This eliminates the need for cumbersome, time consuming and relatively inaccurate additional fine-tuning of patient table positioning. It turns out that correcting the positioning of the scanning volume by adjusting the gradient field and / or by adjusting the spatial encoding during the reconstruction is substantially more accurate and takes less time.
[0025]
Preferably, the position of the patient table relative to the scan volume at which the mask set of magnetic resonance signals is captured is used as a reference position of the patient table relative to the corresponding scan volume for the data set. In this way, the mask magnetic resonance image exactly corresponds to the contrast magnetic resonance image in the corresponding scan volume, and artifacts due to misalignment of the patient table during acquisition of the mask set and the data set are avoided. Is achieved. Thus, the diagnostic quality of the subsequent difference image is considerably improved.
[0026]
It should be noted that the feature of sharing the setting from the preparation sequence and the feature of measuring the position of the patient table to be compared with the reference position can be used independently. In addition, all of these features are technically relevant in that they aim for accurate and fast adjustment of a magnetic resonance imaging system to produce a diagnostically high quality magnetic resonance image.
[0027]
The magnetic resonance imaging system of the present invention is suitable for performing the magnetic resonance imaging method of the present invention. This is actually done by appropriately programming the computer or microprocessor that controls the magnetic resonance imaging system. This microprocessor is included in a control system of a magnetic resonance imaging system, for example.
[0028]
The invention also relates to a computer program as defined in claim 11, which is an independent claim. A computer program according to the present invention enables a control system of a magnetic resonance imaging system to achieve a technical effect for executing the magnetic resonance imaging method of the present invention. The computer program is loaded on a computer or a microprocessor of the magnetic resonance imaging system.
[0029]
The above and other aspects of the present invention will be apparent from embodiments described in detail below with reference to the accompanying drawings.
[0030]
FIG. 1 is a diagram showing a magnetic resonance imaging system in which the present invention is used. The magnetic resonance imaging system includes a set of main coils 10 that generate a stable and uniform magnetic field. The main coil is configured to surround, for example, a tubular inspection space. The patient to be examined is slid into this tubular examination space. The magnetic resonance imaging system also includes a number of gradient coils 11, 12, which generate a magnetic field which exhibits a spatial variation, in particular in the form of a temporary magnetic field gradient in each direction, to be superimposed on a uniform magnetic field. Is done. The gradient coils 11, 12 are connected to a controllable power supply unit 21. The gradient coils 11 and 12 are operated by applying a current from the power supply unit 21. The strength, direction and duration of the gradient field are controlled by controlling the power supply unit. The magnetic resonance imaging system also includes transmit and receive coils 13 for generating RF excitation pulses and for picking up magnetic resonance signals. The transmission coil 13 is preferably constructed as a whole-body coil 13 which can surround (part of) the object to be examined. The whole body coil is usually arranged so that the patient 30 to be examined is surrounded by the whole body coil 13 when it is placed in the magnetic resonance system. The whole body coil 13 functions as a transmitting antenna for transmitting the RF excitation pulse and the RF refocusing pulse. Desirably, the whole body coil 13 is associated with a spatially uniform intensity distribution of the transmitted RF pulse (RFS). Usually, the same coil or antenna is used alternately as a transmitting coil and a receiving coil. Such coils are commonly referred to as "synergy coils." Further, the transmit and receive coils are typically formed as coils, but other geometries are also possible where the transmit and receive coils act as transmit and receive antennas for RF electromagnetic signals. The transmitting and receiving coils 13 are connected to an electric transmitting and receiving circuit 15.
[0031]
Note that a separate receiving coil can be used instead of the above-described embodiment. For example, a surface coil can be used as a receiving coil. Such surface coils have a high sensitivity to relatively small volumes. A transmission coil such as a surface coil is connected to the demodulator 24, and the received magnetic resonance signal (MS) is demodulated by the demodulator 24. The demodulated magnetic resonance signal (DMS) is applied to a reconstruction unit. The receiving coil is connected to the preamplifier 23. The preamplifier 23 amplifies the RF resonance signal (MS) received by the receiving coil, and the amplified RF resonance signal is applied to the demodulator 24. The demodulator 24 demodulates the amplified RF resonance signal. The demodulated resonance signal contains the actual information about the local spin density in the part of the object to be imaged. Further, the transmission / reception circuit 15 is connected to the modulator 22. The modulator 22 and the transmission / reception circuit 15 operate the transmission coil 13 to transmit RF excitation and refocusing pulses. The reconstruction unit derives one or more image signals since the demodulated magnetic resonance signal (DMS) is applied to the reconstruction unit, and these image signals are image information of the imaged part of the object to be examined Represents In practice, the reconstruction unit 25 is preferably constructed as a digital image processing unit 25 which is programmed to derive from the modulated magnetic resonance signal an image signal representing image information of the part to be imaged. The signal on the output of the reconstruction unit is applied to a monitor 26 so that the monitor can display a magnetic resonance image. Alternatively, the signal from the reconstruction unit 25 can be stored in the buffer unit 27 while waiting for further processing.
[0032]
According to the present invention, the patient table 14 with the patient thereon is moved to successive positions, as indicated by arrows 40, and a scan is performed at each position. In practice, the abdominal region of the patient is scanned in a first position, the upper part of the patient's leg is scanned in a second position, and the lower part of the patient's leg is scanned in a third position. At each location, magnetic resonance signals from the scan volume of interest are captured and a magnetic resonance image is reconstructed. The scanning volume is indicated by reference numerals 41, 42 and 43. The patient is located at a first position where the first scan volume of the abdominal region is located such that the isocenter IC of the magnetic resonance imaging system is located within the first scan volume 43. Subsequently, the patient table 14 on which the patient is placed is moved so that the second scanning volume 42 and the third scanning volume 43 are arranged on the isocenter IC. As schematically shown in FIG. 1, the gradient field is adjusted at each location such that its field of view matches the local size of the patient at each location.
[0033]
The magnetic resonance image may be an actual two-dimensional image, but a three-dimensional volume may be reconstructed for each scan volume. Reconstruction unit 25 is desirably arranged to combine the reconstructed image or volume into an overview image or overview volume representing the distal patient's vasculature. Such an overview is particularly indicative of the arterial system with high diagnostic quality and high spatial resolution.
[0034]
The magnetic resonance imaging system according to the invention also comprises a control unit 20 formed as a computer, for example, including a (micro) processor. The control unit 20 controls the execution of the RF excitation and the application of the temporary gradient magnetic field. For this purpose, the computer program according to the invention is loaded, for example, into the control unit 20 and the reconstruction unit 25.
[0035]
When the control unit 20 commands the magnetic resonance imaging system to perform a preparation sequence when the patient is located in the examination zone 50, the gradient coil 12 and the RF antenna 13 perform the preparation sequence for the temporary gradient magnetic field and RF excitation. Is controlled. This preparation sequence is, for example, a relatively simple magnetic resonance signal acquisition sequence. The pre-scan uses this preparation sequence, and an adjustment signal is formed based on information collected by the preparation sequence. For example, a preliminary magnetic resonance image is reconstructed by the reconstruction unit 25 for the magnetic resonance signals acquired during the preparation sequence and displayed on the monitor 26. The operator can then apply an adjustment signal to the control unit 20, for example by pressing a button. Alternatively, the control unit may be arranged to analyze the preliminary image and automatically generate an adjustment signal to start capturing the data set. The modulator 24 provides a subsequent preliminary demodulated signal (p-DMS) which is applied to the control unit so as to obtain a setting suitable for the patient to be examined.
[0036]
Further, a surveying unit 60 provided with an electric position detector, for example, an electric potentiometer device, measures the position of the patient table 14. The surveying unit applies an electrical position signal (POS) representing the position of the patient table to the comparator 61. The comparator compares the position signal (POS) with a reference signal (RFS) stored in the memory 62. The difference between the position signal and the reference signal is calculated by a comparator, which applies a difference signal representing the difference between the position signal and the reference signal to a control input of the control unit. Based on the difference signal, the control unit adapts the currently active scan volume by activating the gradient coil 12 to correspond the currently active scan volume to the reference position. The control unit also adjusts the reconstruction unit 25 to make the current reconstructed magnetic resonance image correspond to the reference position. Preferably, the previously measured position of the patient table is used as a reference position, whereby the current scan volume and the magnetic resonance image correspond to the previous scan volume and the magnetic resonance image.
[0037]
FIG. 2 is a schematic perspective view of the patient table 14 and the gantry 73 of the magnetic resonance imaging system used in the present invention. FIG. 2 is a diagram illustrating a case where the patient's leg is supported by the first gantry 71 at the knee depression and supported by the second gantry 72 at the heel. The second cradle is also provided with a generally L-shaped support 74 for supporting cables 75 and tubes that may be used during the examination of the patient 30.
[Brief description of the drawings]
FIG.
1 is a diagram illustrating a magnetic resonance imaging system in which the present invention is used.
FIG. 2
1 is a perspective view showing a patient table and a gantry of a magnetic resonance imaging system used according to the present invention.

Claims (11)

Using a preliminary scan to capture a preliminary magnetic resonance signal from the subject;
Generating an adjustment signal based on the pre-scan;
Capturing a data set of magnetic resonance signals from each scan volume of the subject;
Capturing the data set is initiated based on the adjustment signal.
Magnetic resonance imaging method. The adjustment signal represents a temporal change in contrast in the object;
The method of claim 1, wherein capturing the data set is initiated based on a comparison of the adjustment signal to a preselected criterion. Capturing a mask set of magnetic resonance signals from each scan volume of interest in a predetermined mask order;
Using the preliminary scan to capture the preliminary magnetic resonance signal from the subject;
Capturing a data set of magnetic resonance signals from each scan volume of the subject in a predetermined data order;
2. The magnetic resonance imaging method according to claim 1, wherein the data order is opposite to the mask order. Capturing the mask set of magnetic resonance signals is performed prior to administering a contrast agent to the subject;
Capturing the pre-scan and the dataset is performed after administering the contrast agent.
The magnetic resonance imaging method according to claim 3. Performing a preparatory sequence that determines one or more settings of the magnetic resonance system associated with each scan volume;
Performing a mask set capture of magnetic resonance signals from each scan volume of the volume in a predetermined mask order;
Using a preliminary scan to capture a preliminary magnetic resonance signal from the subject,
Capturing a data set of magnetic resonance signals from each scan volume of interest in a predetermined data order;
Initiating the acquisition of the data set based on the adjustment signal, a magnetic resonance imaging system,
The data order is the reverse of the mask order,
A magnetic resonance imaging system, wherein the capturing of the mask set, the pre-scanning, and the capturing of the data set are performed using settings from the preparation sequence. A magnetic resonance imaging system, wherein the patient table comprises a support system including a number of platforms. 7. The magnetic resonance imaging system according to claim 6, comprising a support having a substantially L-shaped cross section. A control system for controlling a magnetic resonance imaging system, the control system having an adjustment input for adjusting the control system;
A patient table movable between several scanning positions;
A surveying unit for measuring the position of the patient table at the scanning position,
A comparator for generating a difference signal representing a difference between the measured position of the patient table and a reference value;
6. The magnetic resonance imaging system of claim 5, further comprising a comparator signal output coupled to an adjustment input of the control system. The surveying unit includes a position memory in which the measured position of the preceding scan position is stored;
9. The magnetic resonance imaging system according to claim 8, wherein the stored preceding scanning position is used as the reference value. Using a preliminary scan to capture a preliminary magnetic resonance signal from the subject,
Deriving, from said pre-scan, an adjustment signal representing a temporal change in contrast in said object;
A magnetic resonance imaging system arranged to capture a data set of magnetic resonance signals from each scan volume of the subject,
A magnetic resonance imaging system wherein acquisition of the data set is initiated based on a comparison of the adjustment signal to a preselected contrast. Instructions for using a pre-scan to capture a pre-magnetic resonance signal from the subject;
Instructions for deriving, from the prescan, an adjustment signal representing a temporal change in contrast of the object;
Instructions for capturing a data set of magnetic resonance signals from each scan volume of the subject.
A computer program, wherein the capturing of the data set is initiated based on a comparison of the adjustment signal with a preselected contrast.