Magnetic resonance imaging as a technique for assessing noninvasive tissue ablation using high-intensity ultrasound: an experimental study.
OBJECTIVE
As a form of noninvasive extracorporeal application, acoustic energy offers an alternative to nephron-sparing surgery for renal masses smaller than 4 cm. The availability of a reliable tool for monitoring the therapy is a prerequisite for safe and successful high-intensity focused ultrasound (HIFU) application. The aim of this study was to evaluate the morphologic visualization of HIFU lesions using MRI.


METHODS
We used the ex vivo model of the isolated perfused porcine kidney. Treatment was performed using an experimental HIFU system. Complex lesions were induced in 10 kidneys. MRI was performed under constant perfusion of the kidneys. To determine the exact lesion size, we performed a fat-saturated, T1-weighted, volumetric interpolated breath-hold MRI sequence. For perfusion imaging, we used a three-dimensional fast low-angle shot sequence. Subsequently, the lesions were evaluated macroscopically. The width of the complex lesions was defined as x, the length as y, and the depth as z.


RESULTS
The MRI scans showed good soft tissue contrast in all sequences. The mean difference for the width of the lesions was 0.2 +/- 1.1 mm; for lesion length and depth, it was 1.7 +/- 1.8 mm and 1.1 +/- 1.3 mm for lesion width, respectively. Statistical evaluation of the x values showed no significant difference between the macroscopic and the MRI data (P = 0.85). The y and z values, however, showed a statistically significant difference (P = 0.071).


CONCLUSIONS
MRI could be a diagnostic tool for monitoring HIFU. Before this modality can be used under clinical conditions, further technical development is indispensable, especially with respect to reducing the measuring times.
Honeck
Patrick
P
Department of Urology, University Hospital Mannheim, Germany. patrick.honeck@uro.ma.uni-heidelberg.de
Peters
Kristina
K
Wendt-Nordahl
Gunnar
G
Bolenz
Christian
C
Alken
Peter
P
Michel
Maurice-Stephan
MS
Jenne
Jürgen W
JW
Häcker
Axel
A
D000818:Animals; D017115:Catheter Ablation; D003287:Contrast Media; D007668:Kidney / Q000000981:diagnostic imaging* / Q000601:surgery*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D034421:Sus scrofa; D014465:Ultrasonics; D014463:Ultrasonography
D003287:Contrast Media