MR-guided biopsies of lesions in the retroperitoneal space: technique and results.

The purpose of this study was to evaluate the safety and precision of MRI-guided biopsies of retroperitoneal space-occupying tumors in an open low-field system. In 30 patients with indistinct retroperitoneal tumors [paraaortic lesion (n=20), kidney (n=2), suprarenal gland (n=3) and pancreas (n=5)] MR-guided biopsies were performed using a low-field system (0.2 T, Magnetom Concerto, Siemens, Germany). For the monitoring of the biopsies T1-weighted FLASH sequences (TR/TE=160/5 ms; 90 degrees ) were used in all patients and modified FLASH sequences (TR/TE=160/13 ms; 90 degrees ) in ten patients. After positioning of the needle in the tumors 114 biopsy specimens were acquired in coaxial technique with 16-gauge cutting needles (Somatex, Germany). The biopsies were successfully performed in all patients without vascular or organ injuries. The visualization of the aortic blood flow with MRI facilitated the biopsy procedures of paraaortic lesions. The size of the lesions ranged from 1.6 to 7.5 cm. The median distance of the biopsy access path was 10.4 cm. Adequate specimens were obtained in 28 cases (93.3%) resulting in a correct histological classification of 27 lesions (90%). In conclusion, MR-guided biopsies of retroperitoneal lesions using an open low-field system can be performed safely and accurately and is an alternative to CT-guided biopsies.