MR imaging-guided interventions in the genitourinary tract: an evolving concept

Abstract

MR imaging-guided interventions are well established in routine patient care in many parts of the world. There are many approaches, depending on magnet design and clinical need, based on MR imaging providing excellent inherent tissue contrast without ionizing radiation risk for patients. MR imaging-guided minimally invasive therapeutic procedures have advantages over conventional surgical procedures. In the genitourinary tract, MR imaging guidance has a role in tumor detection, localization, and staging and can provide accurate image guidance for minimally invasive procedures. The advent of molecular and metabolic imaging and use of higher strength magnets likely will improve diagnostic accuracy and allow targeted therapy to maximize disease control and minimize side effects.

Fig. 1

Linear scar through the subcutaneous tissue lies between the transducer and the fibroid, on the sagittal localizer image on the left. The sagittal localizer image on the right is obtained after tilting the transducer superiorly, without moving the patient, allowing treatment planning that will not course through the anterior abdominal subcutaneous tissue scar. (Reproduced from Fennessy FM, Tempany CM. A review of magnetic resonance imaging-guided focused ultrasound surgery of uterine fibroids. Top Magn Reson Imaging 2006;17(3):173–9; with permission.)

Fig. 2

The sagittal localizer image on the left demonstrates bowel loops coursing between the anterior abdominal wall and the uterine fibroid. After placement of a spacer device (sagittal localizer image on the right) under the anterior abdominal wall, the bowel loops are displaced, allowing for treatment through a larger acoustic window. (Reproduced from Fennessy FM, Tempany CM. A review of magnetic resonance imaging-guided focused ultrasound surgery of uterine fibroids. Top Magn Reson Imaging 2006;17(3):173–9; with permission.)

Fig. 3

Imaging of a uterine fibroid pretreatment (A, B) and post-treatment (C) with MRgFUS. Sagittal T2-weighted image (A), obtained with the patient in the prone position overlying the US transducer, demonstrates a large solitary uterine fibroid of low-signal intensity. Sagittal SPGR post gadolinium (B) demonstrates homogenous enhancement of the fibroid. After treatment, sagittal SPGR post gadolinium (C) demonstrates a new large nonperfused area within the fibroid, consistent with treatment-induced necrosis.

Fig. 4

Photograph demonstrating the set-up for percutaneous MR imaging–guided cryotherapy for uterine fibroids in an open horizontal 0.3-T AIRIS II (Hitachi, Tokyo, Japan) scanner. (Courtesy of Yusuke Sakuhara, MD, Department of Radiology, Hokkaido University Hospital, Sapporo, Japan.)

Fig. 5

Axial T2-weighted spin-echo sequence demonstrating a probe in the left anterolateral aspect of a uterine fibroid. The diffuse low-signal intensity in the fibroid represents the ice-ball. (Courtesy of Yusuke Sakuhara, MD, Department of Radiology, Hokkaido University Hospital, Sapporo, Japan.)

Fig. 6

Imaging before and during MR imaging–guided prostate biopsy. Axial (A) and coronal (B) T2-weighted spin-echo sequence outline areas to be biopsied. In this example, an area in the left midgland is demonstrated (arrow), reformatted to the same spatial location as the corresponding real-time axial (C) and coronal images (D) taken during needle insertion. The biopsy needle is seen in cross section as a circle of low-signal intensity (arrow) on the axial gradient-echo real-time image (C) and as a longitudinal area of low-signal intensity (arrow) on the coronal gradient-echo real-time image (D).

Fig. 7

Pre-, intra-, and postoperative MR imaging–guided brachytherapy in prostate cancer. Preoperative 1.5-T (A) axial T2-weighted spin-echo image through the prostate base, demonstrating low signal intensity in the peripheral zone (arrows), previously demonstrated to be tumor. Intraoperative 0.5-T (B) axial T2-weighted spin-echo T2 weighted spin-echo image through the same area. Intraoperative axial gradient-echo MR images (C) obtained in real time during needle and seed placement in the prostate base. The larger round areas represent the needles (arrows), before deployment, and the small round areas represent the deployed seeds (arrowheads). A postoperative axial SPGR (D) through the prostate base demonstrates multiple round areas of low signal in the peripheral zone (arrowheads), consistent with deployed seeds.

Fig. 8

(A) MR imaging–based temperature image during a sonication (130 W for 30 seconds) into rabbit thigh muscle during a test of an MR imaging–compatible transrectal phased array applicator for MRgFUS of prostate. (B) The thermal lesion (arrow) seen in T2-weighted imaging. The bright region to the right of the lesion is a tissue fascia layer. (From Sokka SD, Hynynen K. The feasibility of MRI-guided whole prostate ablation with a linear aperiodic intracavitary ultrasound phased array. Phys Med Biol 2000;45:3373–83; with permission.)

Fig. 9

MR imaging–guided catheter-based US thermal therapy of the prostate: real-time temperature image (left), maximum temperature image (middle), and thermal dose (right) of the prostate during catheter-based US thermal therapy. The transurethral catheter, with a rotating curvilinear transducer array, is depicted as the round low-signal intensity structure within the prostate gland. (Courtesy of Kim Butts Pauly, PhD, Viola Rieke, MD, and Graham Sommer,PhD, Stanford University School of Medicine, Stanford, CA; and Chris Diederich, PhD, UCSF, SanFrancisco, CA.)

Fig. 10

CT–guided percutaneous cryotherapy of renal yumors. A 77-year-old woman who had RCC of the right kidney upper pole. Unenhanced transverse CT images obtained during percutaneous cryoablation performed in the right lateral decubitus position show that (A) low contrast-to-noise ratio and poor edge definition of ice ball (arrows) in the perinephric fat renders assessment for overlap of ablation zone with adjacent adrenal gland (arrowhead) difficult, and (B) streak artifact from applicator interferes with visualization of portion of the ice ball (arrow).

Fig. 11

MR imaging–guided percutaneous cryotherapy of renal tumor. A 70-year-old man who had RCC of the right kidney lower pole treated with MR imaging–guided percutaneous cryoablation. (A) Transverse T2-weighted fast recovery fast spin–echo sequence image obtained before treatment in 1.5-T MR image shows a small exophytic renal mass in the lower pole of the right kidney anteriorly (arrow). (B) Intraprocedural transverse gradient-echo image obtained in 0.5-T open configuration interventional MR imaging shows that sharp edge definition of signal void ice ball (arrows) contributes to monitoring of tumor coverage and assessment of proximity to adjacent ureter (arrowhead), renal collecting system (+), and colon (*), which is being displaced by an interventionalist’s hand (curved arrow). (C) An 18-month follow-up contrast-enhanced transverse CT image shows no enhancement in the involuted ablation zone (arrows).