Endorectal coils boost accuracy of MR prostate cancer diagnosis

Patients hate endorectal coils. But results presented at RSNA 2004 show without equivocation that the devices boost the diagnostic confidence of imaging studies critical to determining how prostate disease should be properly managed.

New studies of MR spectroscopy, dynamic contrast-enhanced MR imaging, and ultrasmall paramagnetic contrast medium show that these approaches also improve diagnosis and provide useful information for patient management.

Under the guidance of Dr. Hedvig Hricak at Memorial Sloan-Kettering Cancer Center, Dr. Liang Wang confirmed that an endorectal coil boosts the resolution and diagnostic confidence of MRI and multivoxel MRSI for determining whether prostate cancer is confined within the borders of the organ.

Based on experience with 411 patients, including 268 cases in which both MRI and MRSI were used, Wang found that exams employing a coil enabled the clinician to stage cancer with significantly increased accuracy. The average Partin nomogram score with imaging results drawn with the use of a coil was 0.8327 compared with 0.7769 without a coil. Exams performed with MRSI were even more accurate, Wang said.

Dr. Juan Vilanova, a radiology researcher at Clinica Girona in Girona, Spain, demonstrated the value of endorectal coil-assisted MRI and 3D MRSI imaging for reevaluating patients with elevated prostate-specific antigen levels that persisted after a negative biopsy. Prostate cancer was positively identified in 10 of 27 cases.

Cancer was found in the transitional zone of four patients and the peripheral gland of six patients. In the positive cancer cases, the choline + creatine/citrate ratio and choline/creatine ratios for voxels in the transitional zone were significantly different (p>0.01) from ratios in the voxels with benign prostatic hyperplasia. For the peripheral gland, the CC/Ci and Ch/Cr ratios for cancer voxels were significantly different from the ratios in voxels sampled in normal tissue, Vilanova said.

The protocol's overall accuracy, sensitivity, and specificity were 85%, 75%, and 87%, respectively. Vilanova recommended that 3D MRSI should be routinely prescribed for patients whose PSA levels continue to be elevated after negative biopsy. He cautioned radiologists, however, to carefully survey the entire gland as well as the transitional and peripheral zones when performing the procedure.

Dynamic contrast-enhanced MRI can assist follow-up therapeutic planning for recurrent prostate cancer after radiation therapy, according to Dr. Masoon A. Haider, an assistant professor of radiology at Princess Margaret Hospital in Toronto. A study of 37 patients demonstrated that early intense enhancement on DCE-MRI uncovers locally recurrent prostate cancer. Sensitivity and positive predictive value rates of 72% and 88%, respectively, showed that the dynamic contrast technique is far superior to conventional T2-weighted MRI for this role. The enhancement pattern also aids planning for follow-up minimally invasive therapy.

Ultrasmall iron-oxide contrast continues to show promise for detecting nodal involvement in prostate cancer. Dr. M.G. Harisinghani, a researcher at the Center for Molecular Imaging Research at Massachusetts General Hospital, employed ferumoxtran-10 to discover that metastastic prostate cancer usually first involves lymph nodes located within 2.5 cm of the anterior surface of lumbar vertebral bodies. His study of 21 prostate patients also found that all positive nodes were localized within 1.2 cm of the aorta. These findings may aid biopsy and therapeutic planning, he said.