JPS63203144A - Calibration phantom for quantitative computer tomographic system for measuring mineral of bone - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The use of a calibration reference phantom for use with computerized tomography (CT) systems substantially improves the utilization of such systems for the measurement of bone density. It has been demonstrated for clinical medical use at the University of California at San Francisco to provide augmentation. Such innermost computed tomography (QCT) systems have provided early detection and accurate long-term monitoring of osteoporosis patients in more than 300 clinical medical devices. The first characteristic f for the calibration phantom
l' (Donald J, Volf (Donald J
.

VOIZ) U.S. Patent No. 4,233°5
No. 07) discloses in that patent a general technique of using simultaneously scanning calibration phantoms.

As described in this patent, the phantom is placed under the patient and it and the patient are simultaneously scanned with a CT scanner, thus improving the performance of the CT scanner.
” Due to various technical factors in the process, the standard Li
111 servings. The phantom can be manually installed by the operator (
In order to be able to calculate the mineral density of a patient's bone (or more recently with a programmed computer), a series of reference elements is provided whose graded density corresponds to the varying mineral content of human bones.

This invention relates to an improved calibration phantom as taught by Dr. Donald J. Volf in US Pat. No. 4,233,507.

In a preferred embodiment as described in the phantom, the phantom includes a molded base member formed from urethane having a series of closely spaced, elongate, cylindrical cavities formed within the urethane base member. . A plurality of these cavities are filled with a predetermined 111 degree solution with an X-ray attenuation rate corresponding to human bone, and one cavity is filled with distilled water.

These solutions are in direct contact with the urethane material, i.e.
The solution is in direct contact with the support material nLl, thus the base material of the phantom forming the vessel. Prior to sealing, the filled cavity is subjected to a degassing procedure to ensure that substantially all gases and bubbles are removed from the solution.

Each cavity is then capped as a vacuum seal and with a stopper advantageously designed to apply substantial pressure to the encapsulated solution and maintain such pressure over the life of the phantom.

The construction of the phantom in this manner provides a high strength phantom with low permeability to liquid Δ3 and gas. Lower physical W of urethane material products! The power and atomic number reduce total x-ray attenuation due to reduced beam enhancement and x-ray dispersion relative to prior art phantoms.

The resulting phantom constructed in accordance with the present invention has a number of important advantages.

1. This phantom has X-ray attenuation characteristics that are extremely similar to those of human muscles. Human musculature typically has a CT number of approximately 32 expressed in ``1'' units, and phantoms constructed in accordance with the present invention typically have a CT number in the range of approximately 12 to 33 units (CT?8). As a result.

The interaction of X-rays in J3 with the phantom is human muscle Δ3
The image artifacts in the phantom image are reduced due to the similarity of the XrA reduction and dispersion of the phantom and patient being in close proximity to each other.

2. Urethane is a very strong and indestructible material, thus overcoming the brittle characteristics of prior art phantoms. Furthermore, the thickness of the cavity walls is reduced so that overall, this phantom can be significantly narrower and thinner than the prior art phantom. This reduced size and total mass results in less beam intensification and dispersion, and also on the table and CT
It provides for improved ease of positioning the patient in the field of view. Furthermore, the radiation m given to the 18 persons is reduced by the radiation-reduced attenuation. The high strength of urethane further facilitates the use of high pressures with reference solutions.

3. Urethane materials have extremely low permeability to water and gas. As a result, the integrity of the reference solution is maintained for a long time. Furthermore, the low permeability of the urethane material allows the wall thickness to be extremely nD between the top and bottom surfaces of the phantom and the reference cavity. Reduced wall thickness and therefore reduced phantom size produce less beam intensification and dispersion and hence reduced image artifacts.

4. The chemistry of the urethane material provides a rigid phantom or, if selected, a flexible phantom that can be contoured into a variety of shapes, including contouring to the patient's body. can be selected.

5. The urethane material is translucent, allowing visual verification of the absence of air bubbles on the reference element.

6. The liquid reference element and urethane base provide for very homogeneous X-ray attenuation characteristics providing minimal structural changes during attenuation, ie structural noise in the 07 image. This increases the accuracy of G, ifi measurements.

The conventional teaching of the prior art is that the solution container is made of a different material than the phantom base material.

Typically, a sealed thin-walled polyethylene tube filled with a reference solution is embedded in an acrylic base. These prior art materials typically have CT numbers of J3 to 801-1 units, and their X-ray attenuation properties are significantly higher than human muscle tissue.

Additionally, prior art phantoms have a base member <a
a) requiring physically large and heavy members with significant thickness of material between the reference solution tube and the outer wall of the phantom; and (b) between adjacent tubes. This substantial size and mass of the pace material is x1
1. Significant a.1 X-ray dispersion and beam intensification of the beam and creating an increased image artifact.

This invention is therefore a substantial departure from prior art phantoms since the phantom base itself has a number of important advantages over prior art devices - it provides a standard solution container at all times; It is completely different.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, a top-down view of a conventional CT scanner 10 illustrating the position of a calibration phantom 11 is shown. As shown, the zero scanner includes a gantry 12 . Although not shown, it will be appreciated that the gantry 12 supports an x-ray source and collimator and a juxtaposed x-ray detector, as is known. The patient 13 is moved through the movable platform 14 through the gantry opening 15. It is positioned at L. As shown, a series of Kutsushiron 2
0.21 and 22 are supported by this pedestal as well as the calibration fan 11. Water etc. 1) Gel (not shown)
A Pols bag containing the phantom is optionally placed between the top of the phantom and the patient to eliminate or reduce the air gap between the phantom and the patient's body curves.

As in the Volf patent in L.L., the phantom of the present invention is designed such that each cross-section of the CT scan includes the hydraulic force of the calibration phantom on the patient and that part of the body overlying the phantom. The top of the table extends longitudinally along the top of the table and includes a series of elongated shims of reference material juxtaposed with the table and the patient.

The shape and physical structure of the calibration phantom is shown in FIGS. 2-6, 8, and 9. As shown, the phantom 11 has a plurality of longitudinal cavities 2G, 2
7.28.29 and 30 include an elongate, slightly arcuate base 25 which is molded as a single piece with spaced C's spaced side by side therein. In addition, an elongated small diameter metal rod 35 and 3G is attached to the base 25 for positioning the CT cursor in the area of interest on the image.
It may be molded into a computer and used manually by an operator or autonomously by a CT scanner system.

Each of the cavities 26-30 is right-handed with a rounded end 40 and an open end 41.

In a preferred embodiment of this invention, the end 41
is threaded as shown at 42 to receive a threaded cap and O-ring sealing member 43. A pair of apertures 44 (best shown in FIGS. 8 and 9) are provided for receiving a closure to rotate the closure within the threaded opening 41 to a desired depth.

Preferred materials for constructing the base 25 and closure plug 43 are compounded aliphatic isocyanates and polyether resins in reaction injection molding fittings (RIM), as well as adducts of one or more catalysts and stabilizers. It is a urethane formed by The specific formulation components of urethane used to construct this phantom were manufactured by Qood Marc Chemical Co., Costa Mell., California.
Formulation No. QMC-462, supplied by Als, Ino, ). Stabilizers and/or catalysts are utilized to control solidification rate and temperature and strength as well as to prevent the urethane from discoloring or yellowing when exposed to diffuse radiation. The particular aliphatic urethanes utilized in this invention have the properties of being stable in the presence of water without material loss or failure, low viscosity to allow molding without creating bubbles in the phantom base, and J3 per cubic centimeter 1. It has a physical density of 03 to 107 grams.

The urethane has a water-white color that is UV stabilized, thereby avoiding yellowing, and may advantageously be dyed to provide different colors.

The resulting phantom base 25 also has very low permeability to water and gases, while being an extremely strong container for the reference calibration element. As a result, the wall thickness (T) between the upper and lower surfaces of the phantom base and the juxtaposed cavity walls (as shown in FIG. 4) is extremely thin, typically with a thickness of 3I. obtain. As a result, for a given size phantom, the tubular cavities 26-30 minimize beam enhancement and XF2 dispersion and reduce image artifacts, while improving photon statistics for improved accuracy. It has the same large cross-section as is possible with a phantom of a given size. Additionally, the impermeable, high-strength walls ensure that the liquid calibration sample is under high pressure to ensure a stable reference over long periods of time by prohibiting any inflow or outflow of water or gas or the formation of air bubbles. allow it to be maintained under the It is important to note that reference solutions are used for medical diagnosis and as such must be known and maintained with high accuracy over time.

This urethane material is also particularly advantageous in that it provides a homogeneous phantom without attenuation variation across the cross-section of the phantom body. Additionally, the urethane material is translucent so that any bubbles in the liquid reference solution can be easily observed. Additionally, as explained below, the physical properties of the urethane material can be varied to provide either a rigid phantom or a flexible phantom that can be contoured to the patient's body.

As explained in the Borno patent above, several calibration samples were prepared using a series of graded dipotassium hydrogen phosphate solutions (K2 HPO< ) is advantageously formed from. Calcium carbonate (CaCo, ) and calcium hydroxyapatite Cas<PO2), (01-1>) are also used to simulate the X-ray attenuation of human bones19.Of course, this invention also applies to bone mineral analysis. Hole tissue such as human muscle and blood with iodine contrast material that can be used in place of calibrating CT scanners for other diagnostic uses in phantoms, but not only for systems It will be appreciated that samples having similar attenuation characteristics may be included.

The process of manufacturing the calibration phantom 11 is shown in FIGS. 3 and 6.
As shown in the figure. As shown in FIG. 3, the base cavity 28 is filled with a calibrated M quasi-solution 45. As shown in FIG. 6, when each cavity 26-80 is filled with its own constituent solution, the entire base member 2
5 is installed in a suitable gas handling chamber 50. Chamber 5
0 includes a conventional vacuum system including a Pel Jar 51 and a vacuum pump or other a52 for evacuating and emptying the chamber within the Pel Jar 51 to handle gases and bubbles from the respective solutions. Their
It has been found advantageous to avoid any changes in the linear attenuation rate.

Another technique for degassing the solution is to lower the filled base 25 into a water bath coupled to an ultrasonic transducer (not shown) and remove any air bubbles in the reference solution by ultrasonic levitation. It is also to remove the . 40
A standard ultrasonic bath cleaner with KH2 frequency may be used.

As a result, no matter which degassing technique is used,
Any gas that is in the calibration solution or that enters when the solution is injected into the cavity or any air bubbles that become trapped on the walls of the cavity will be removed into the final sealant of the reference solution.

1. Alternative embodiments of the member 43 are shown in FIGS. 8j3 and 9.
As shown in the figure. In Example 43a of FIG. 8, O
The ring 55 is retained in an annular groove 56 in the side wall of the threaded plug 57 to provide a tight ring seal between the plug 57 and the side wall 58 of the cavity. In another embodiment 431), the O-ring 6o is placed at the bottom of the shoulder 61 seen on the bung 62 so that a seal is formed as the bung 62 presses the O-ring against the abutment 8I163 at the mouth of the cavity 111. is retained. Sealing member 4
3a and 43b are screwed into the threaded cavity opening of the phantom base sufficiently to apply a significant pressure, i.e. on the order of 100 psi, to the encapsulated liquid calibrated reference solution. It will be done. Bubble formation is therefore further prevented.

In the embodiment shown in FIG. 4, cavities 26-30 are formed with a circular cross-sectional shape. In an alternative embodiment, cavity 7
0.71, 72, 73, and 74 are formed in a generally square shape that makes somewhat more efficient use of the interior space of the base member.

However, both embodiments may be made quite compact while maintaining the required diameter of the calibration cavity diameter, for example 2° Ocm. Thus, in one embodiment of a calibration phantom having the external shape of FIG. 2 and the cross-sectional shape of FIGS. 3 and 7, the overall shape of the base member has a radius of curvature on the recess side of 55.80 m; Shaped slightly crescent-shaped with a length of 36 cm, a width W of 160111, and a depth D of 2.6 CI, each of the cavities 21 to 36 is roughly 2.6 cm in diameter. It is Ocm. Comprehensive type 1 is 3°5 bond.

In contrast, the acrylic-based prior art phantoms currently in use are considerably larger and heavier, typically having a length of 46 cn+, a width of 26.5 CI, and a depth of 4 cm. The total weight is 10.5 bonds. Since the tubes embedded in these prior art phantoms are approximately the same diameter as the cavities of the present invention, the prior art provides a It is clear that a substantially greater thickness of base material is presented than in a phantom constructed according to the present invention.

Typical CT section drawn showing patient 13 and phantom 11 properly positioned ii! , j images are shown in FIG. Typically, four phantom reference elements 80, 81, 82 and 83 provide a calibration for calculating the bone mineral density of a patient's vertebrae, and the concentration of 28PO, in distilled water, is typically are 0150.100 and 200z/cc, and the fifth element (for example, element 85) is a sample similar to fat hit ff1W.

In a typical test, the mineral content m for tissue bodies for four T7 vertebrae is determined and averaged to obtain a single result for the patient.

) The strength and stiffness of the 7-tontom may be modified by changing the chemical properties of the urethane. Thus, the rigid phantom can be modified using conventional techniques to provide a flexible phantom base in which the urethane chemistry is contoured into a variety of configurations, including contouring to the patient's body. Therefore, it can be constructed using urethane material. For example, a soft phantom can be contoured to the patient's column, lower back, or legs.

It will also be appreciated that the calibration sample need not be made of a liquid composition. In this way, Nampurus is mixed with urethane and Kzl-IPOn to constitute a solid rod which is then placed in a hollow cavity instead of a liquid solution.
or a mixture of urethane and calcium hydroxyapatite. Instead, solid material calibration samples are directly attached together to form a solid phantom, such that all or substantially all of the phantom is comprised of solid sample elements.

Calibration samples and phantom base members can be formed from other plastic-like materials with desired physical and X-ray attenuation properties, such as those sold under the trademark TPX by Mitsui Petrochemical Industries, Ltd. It will also be appreciated that polyolefin polymers may be used and may have the added advantage of being injection molded.

[Brief explanation of the drawing]

FIG. 1 is a front view of a computed tomography system with a calibration phantom in place. FIG. 2 is an exploded perspective view showing the installation of the cavity plug on the phantom base. Figure 3 shows the filling of the calibration phantom with the reference solution.
3 is a cross-sectional view taken along line 3-3 of the figure; FIG. Figure 4 shows a reference cavity PA4 with a circular cross-sectional shape.
FIG. 4 is a cross-sectional view taken along line -4. FIG. 5 is a cross-sectional view of another embodiment of a calibration phantom showing a reference cavity having a generally square cross-sectional configuration. FIG. 6 is a perspective view showing the use of a vacuum pump and pelger to degas the reference solution during the manufacture of the calibration fan. FIG. 7 is a diagram of a typical transaxial cross section provided by a CT scan. FIG. 8 is a cross-sectional view of one embodiment of a plug used to seal the reference cavity of the phantom base. FIG. 9 is a cross-sectional view of a second embodiment of a sealing plug used to seal the reference cavity of the phantom base. In the figure, 1 is a CT scanner, 11 is a phantom, 1
2 is a gantry, 14 is a movable platform, 15 is a gantry opening, 20.21
and 22 is Kutsushikon, 25 is Pace, 26.27.
28.29J5 and 3o are cavities/cavities, 35 and 36 are metal rods, 41 is an open end, 43 is a sealing member, 44 is an opening, 45 is a reference solution, 50 is a gas handling chamber, 51 is a Pelger, 55 is an O-ring, 56 is an annular groove, 57 is a screw stopper, 60 is an O-ring, 62 is a stopper, 70.71.72.
73 and 74 are cavities, and 80, 81, 82 and 83 are reference elements of the phantom. -No.;mu-~ZT , Relationship to the case of the person making the amendment Patent Applicant Address: Irvine Sandstone, California, United States of America, 4 Name: Allen Ken Arnold 4, Agent Address: 1 Hirano-cho, 2-8 Hirano-cho, Higashi-ku, Osaka City Chiyo Building Telephone Osaka (06) 222-0381 (Main) 6
, all drawings subject to amendment 7, contents of amendment as attached. Please note that there are no changes to the content. that's all

Claims (14)

[Claims] (1) A series of graded reference solutions with X-ray attenuation properties very similar to those of human tissue are held within a cavity formed by a translucent member in direct contact with the material forming the phantom base. , a calibration phantom for a quantitative computed tomography (QCT) system for bone mineral measurements, further characterized in that the cavity minimizes the size and mass of the phantom and thus further enhances and disperses the x-ray beam. and placed in close proximity to the upper and lower surfaces of the phantom to minimize image artifacts, and 16 to 33 in close proximity to human musculature.
a generally crescent-shaped base formed of a strong material with X-ray attenuation properties having a CT number in the range of H units; a plurality of elongated cavities formed in said base; in contact and the upper and lower surfaces of the base are in close proximity to the reference solution with a base material thickness of approximately 3 mm between the upper and lower surfaces of the base and the retained reference solution. a series of graded concentrations of reference solutions held within said cavity having X-ray attenuation properties corresponding to human bone; applying a pressure on the order of 100 psi to said liquid; a stopper that both seals the opening for receiving the solution in the base material, the base material being such that no visible outgassing from the material to the encapsulated liquid occurs and that the base material is characterized by being a highly stable material with extremely low permeability to water and gases, so as not to allow any inflow or outflow of gases or liquids into the solution;
Calibration phantom. (2) The calibration phantom of claim 1, wherein the base is formed from a urethane material. 3. The calibration phantom of claim 1, wherein the base is formed from a material having a CT number in the range of approximately 12 to 33 H units. (4) The external surfaces of the plurality of calibration reference elements are determined by the size and mass of the phantom and thus the intensification of the x-ray beam;
A calibration phantom for a CT system that is placed in close proximity to the upper and lower surfaces of the phantom to minimize dispersion and image artifacts, and has X-ray attenuation characteristics that closely approximate human muscle. the base member is formed from a strong material that has an ultra low permeability to water and gases, the base member having an upper surface for placement in close proximity to the patient, and having a closed end and an open end. a plurality of longitudinal cavities formed in said base having sealable ends; and a series of graduated elongate cavities retained within said cavities having X-ray attenuation characteristics corresponding to human bone or tissue. a wall thickness between the reference solution and the cavity wall juxtaposed with the upper and lower surfaces of the base having a minimum thickness so as to minimize X-ray beam intensification, dispersion, and image artifacts; and a plug for sealing the open end of the cavity while applying significant pressure to the solution encapsulated therein. (5) a calibration reference solution is placed in direct contact with the material forming the phantom base, and the phantom base is formed from a material with X-ray attenuation properties compatible with human tissue to minimize image artifacts; A calibration reference phantom for a CT system that is designed to have X-ray attenuation properties very close to those of human tissue, and a base made of a strong material with very low permeability to water and gases, and a cavity. a plurality of elongate cavities formed in the base material such that the walls are formed by the base material, the cavities having a closed end and an open sealable end. , a series of graded reference solutions held within the cavity such that the solutions are in direct contact with the base material, the reference solutions being such that the x-ray beam of the CT scanner corresponds to the x-rays of human tissue; passing only through materials with attenuation properties or through a reference solution, thereby strengthening the X-ray beam,
Calibration phantom with X-ray attenuation properties corresponding to human bone or tissue to minimize dispersion and artifacts. (6) The calibration phantom of claim 5, wherein the base is formed from urethane. (7) reaction injection molded from a mixture of aliphatic isocyanate and polyether resin to form a strong urethane material with extremely low permeability to water and gas;
A calibration phantom according to claim 5. (8) A thread is cut so that the open end of the cavity pairs with a corresponding thread on the sealing stopper, and an O A calibration phantom according to any of claims 5 to 7, wherein the ring maintains a tight seal against the inflow and outflow of liquids and gases. (9) A thread is cut so that the open end of the cavity mates with a corresponding thread on the sealing stopper to maintain a tight seal against the inflow and outflow of liquids and gases. Claims 5 to 5, wherein the plug has an annular groove and an O-ring retained within the groove such that the O-ring forms a seal between the plug and the wall of the cavity. Calibration phantom according to any of clause 7. (10) The open end of the cavity is threaded to mate with a corresponding thread on the sealing stopper, and the stopper has a shoulder formed in the stopper and an O-ring placed therebetween. having juxtaposed abutments at the cavity opening with an abutment that maintains the fluid under pressure when the stopper is screwed into the cavity opening and allows liquid to and from the reference solution held within said cavity. and pressure is applied to the O-ring seal to provide a tight seal against the inflow and outflow of gas while also simultaneously applying pressure on said fluid.
The calibration phantom according to any one of paragraphs 7 to 7. (11) Molding the phantom base from a strong material with X-ray attenuation properties very similar to those of human muscle and having extremely low permeability to water and gases, and further forming a plurality of foams within said foam base during such molding process. filling one or more of said cavities with a reference solution having X-ray properties corresponding to different human bone or tissue densities; sealing the open end of each of the cavities to prevent solution outflow and gas inflow into the solution. A method for manufacturing a calibration phantom for a CT system, through which X-rays pass. (12) A method for manufacturing a phantom according to claim 11, comprising the step of degassing the solution before the open end of the cavity is sealed. (13) Applying pressure to a reference solution in at least one of the cavities and maintaining the reference solution under pressure after the cavities are sealed.
Method of manufacturing the calibration phantom described in Section. (14) A calibration phantom for a CT system with minimal x-ray beam enhancement, dispersion, and image artifacts, the external surfaces of a plurality of calibration reference elements being close to the top and bottom surfaces of the phantom. a base formed of a strong material having X-ray attenuation properties very similar to those of human muscle and having very low permeability to water and gases, said base member being placed in close proximity to the patient; a calibration phantom comprising a series of graded reference elements integral with said base having an upper surface having X-ray attenuation characteristics corresponding to human bone or tissue;