DOI: 10.1148/radiol.2283020911
System for MR Image–guided Prostate Interventions: Canine Study1
Robert C. Susil, BS,
Axel Krieger, MS,
J. Andrew Derbyshire, PhD,
Attila Tanacs, BS,
Louis L. Whitcomb, PhD,
Gabor Fichtinger, PhD and
Ergin Atalar, PhD
1 From the Departments of Biomedical Engineering (R.C.S., E.A.), Mechanical Engineering (A.K., L.L.W.), Computer Science (A.T., G.F.), and Radiology (E.A.), Johns Hopkins University School of Medicine, 720 Rutland Ave, Traylor Bldg 330, Baltimore, MD 21205; Laboratory of Cardiac Energetics, National Institutes of Health, Bethesda, Md (J.A.D.); and Department of Electrical Engineering, Bilkent University, Ankara, Turkey (E.A.). Received July 31, 2002; revision requested September 30; revision received October 28; accepted December 10. Supported in part by NIH grants R01 HL57483 and R01 HL61672. Additional support from NSF grant ERC 9731478 and U.S. Army grant PC 10029. R.C.S. supported by an NIH training grant. Address correspondence to E.A. (e-mail: eatalar@mri.jhu.edu).
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Figure 1. Rectal sheath and needle guide. A, A stationary rectal sheath with a radius of 1.5 cm forms a stable access route through which the prostate can be reached. A single-turn rectal imaging coil with tuning, matching, and decoupling elements is included in the sheath. A cylindrical needle guide (B) is placed inside the stationary rectal sheath (C), allowing rotational and translational degrees of freedom. D, The needle guide includes three tracking microcoils and a curved needle channel, which allows access to the prostate laterally through the rectal wall.
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Figure 2. Assembled interventional device. A, The stationary rectal sheath and needle guide are affixed to the positioning stage. With use of a flexible articulated arm and a linear track, the device can be positioned freely until both the arm and the track are locked into position. The positioning mechanism converts rotation of the two concentric control rods into rotation and translation of the needle guide within the stationary rectal sheath. B, The sheath is positioned inside the rectum and held stationary by the positioning arm and linear track. C, By rotating the two control rods located outside the bore, the needle guide can be positioned within the rectum.
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Figure 3. Needle insertion and therapy delivery. A, A variable stop is used to control the depth of needle insertion. B, After the trocar (ie, inner stylus) is removed, the cannula remains as a hollow conduit through which fluid can be injected into the prostate. C, To place brachytherapy seeds, the trocar and cannula are first advanced together. D, Then, after the trocar is withdrawn, a brachytherapy seed is pushed to the end of the cannula with a second trocar. E, With the trocar held stationary, the cannula is withdrawn, ejecting the seed into the tissue. The trocar and cannula are then withdrawn together.
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Figure 4. Accurate placement of needles in the canine prostate with use of the transrectal needle guide and microcoil tracking. Top: Four target points in an anesthetized canine were selected on transverse T1-weighted fast SE MR images (700/9.2, bandwidth of ±31.25 kHz, echo train length of four, 16-cm field of view, 3-mm section thickness, 0.5-mm intersection spacing, 256 x 256 matrix, four signals acquired, imaging time of 3 mimutes). Bottom: Transverse T1-weighted fast SE MR images were obtained again after needle placement. The needle tip artifact and the target were found on the same image section, with an in-plane separation of less than 2 mm. Also note that there was minimal motion of the prostate upon needle insertion.
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Figure 5. Coronal fast SE MR images (700/9.2, bandwidth of ±31.25 kHz, echo train length of four, 8-cm field of view, 1.5-mm section thickness, 256 x 256 matrix, four signals acquired, imaging time of 3 minutes) obtained in a gel phantom show artifacts created by A, the prostate needle and B, the brachytherapy seed. Both objects created a uniform signal void along their lengths and a circular bloom, centered on the object tip, at the end facing the positive pole of the static magnetic field. The labeled arrow (B0) denotes the positive direction of the static magnetic field. The artifacts were aligned by placing the physical objects (ie, needle and seed) at the interface of gadopentetate dimeglumine-doped and gadolinium-free gel blocks.
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Figure 6. Intraprostatic injections of a solution consisting of 0.4% trypan blue dye and 30 mmol/L of gadopentetate dimeglumine depicted on fast spoiled GRE MR images. The box on the sagittal scout MR image (left) indicates the location of the time-series images (6/1.5, 90° flip angle, bandwidth of ±62.5 kHz, 16-cm field of view, 10-mm section thickness, 256 x 160 matrix, acquisition time of 0.96 second per image). Note that all of the injected contrast agent-dye solution remained in the canine prostate. Therefore, it was confirmed that the full desired dose was delivered to the tissue. t = elapsed time between the beginning of contrast agent administration and the image acquisition.
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Figure 7. Distribution of injected contrast agent-dye solution depicted on transverse fast spoiled GRE MR images (80/2.0, 60° flip angle, bandwidth of ±31.25 kHz, 16-cm field of view, 3-mm section thickness, 0.5-mm intersection spacing, 256 x 256 matrix, four signals acquired, imaging time of 1 minute 20 seconds) and confirmed in gross tissue slices. The distribution of the gadolinium-blue dye solution as visualized with MR imaging (enhancement seen in postinjection but not preinjection MR images) matches with the distribution of blue-stained tissue seen in the gross tissue slices.
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Figure 8. MR image-based monitoring enables detection of faulty injections. The box on the sagittal scout MR image (left) indicates the location of the time-series MR images (6/1.5, 90° flip angle, bandwidth of ±62.5 kHz, 16-cm field of view, 10-mm section thickness, 256 x 160 matrix, acquisition time of 0.96 second per image). In this canine, the injected contrast agent-dye solution leaked out of the prostate and into the surrounding connective tissue. Therefore, it was known—during the procedure—that the desired dose had not been delivered to the prostate. t = elapsed time between the beginning of contrast agent administration and the image acquisition.
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Figure 9. Leakage of injected contrast agent-dye solution into surrounding tissue is confirmed on transverse fast spoiled GRE MR images (80/2.0, 60° flip angle, bandwidth of ±31.25 kHz, 16-cm field of view, 3-mm section thickness, 0.5-mm intersection spacing, 256 x 256 matrix, four signals acquired, imaging time of 1 minute 20 seconds) and in the corresponding gross tissue slices. The distribution of the gadolinium-based solution, seen as an area of high signal intensity (arrows) on the MR images, correlates with the distribution of the solution seen in the stained canine prostate tissue sections. Although some solution remained in the prostate, some solution also passed into the connective tissue at the superior left margin of the posterior region of the prostate.
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Figure 10. MR image guidance enables accurate placement of brachytherapy seeds in a canine prostate. A, Three target areas in one plane of the prostate were selected on coronal fast SE MR images (700/9.2, bandwidth of ±31.25 kHz, echo train length of four, 16-cm field of view, 3-mm section thickness, 0.5-mm intersection spacing, 256 x 256 matrix, four signals acquired, imaging time of 3 minutes). B, The needle was placed at these locations as described previously. Because the brachytherapy seeds were placed at the end of the cannula (2 mm back from the end of the trocar tip), the needle artifact extended beyond the target site by approximately 2 mm. In C, the seeds have been placed in the prostate. The black bloom artifact at the superior end of the 4-mm brachytherapy seeds is visible. The seeds extended 4 mm from this artifact in the inferior direction.
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Copyright © 2003 by the Radiological Society of North America.
