High-Resolution Diffusion–Weighted MRI Detects Low-Volume Tumors

Indian Wells, California—Multiparametric magnetic resonance imaging (MP-MRI) can be used to identify larger tumors in candidates for prostatectomy. However, according to Ali-Reza Sharif-Afshar, MD, and colleagues, not all tumors are visible on MP-MRI; many small tumors found in patients on active surveillance are below the limits of detection, creating a need to characterize the long-term natural history of low-volume tumors and target them for biopsy.

The researchers recently conducted a study to introduce a novel high resolution diffusion-weighted imaging (HR-DWI) sequence and compare it to standard DWI (S-DWI). They reported results of the prospective pilot trial during a poster session at the 91st Annual Meeting of the Western Section of the American Urological Association in a poster titled Prospective Pilot Study of a Novel High Resolution Diffusion-Weighted Prostate MRI.

The HR-DWI and S-DWI were integrated into a routine MP-MRI protocol and read by two radiologists. The primary outcome measurements were comparisons of suspicious lesions detected by S-DWI and HR-DWI with a standard 12-core biopsy in patients on active surveillance.

Compared to S-DWI, HR-DWI produced a five-fold improvement in spatial resolution. In the clinical trial, the researchers considered the diagnostic characteristics of MP-MRI for each of six zones of the prostate: left/right-base/mid/apex. MP-MRI incorporating S-DWI was useful for predicting biopsy results (area under the curve [AUC] 0.72; Fisher’s exact P<.001). However, MP-MRI was more highly predictive of biopsy results using HR-DWI (AUC 0.88; Fisher’s exact P<.001). AUC for MP-MRI incorporating HR-DWI was significantly larger than MP-MRI incorporating S-DWI (P =.002).

In sensitivity analyses, MP-MRI using HR-DWI had a sensitivity of 95.7%, identifying tumor in 22 of 23 zones proven to have cancer on biopsy, compared with a sensitivity of 60.9% with S-DWI, which identified 14 of 23 biopsy-positive zones (P =.004). While these results require validation, the researchers said they demonstrate the use of a novel HR-MRI that can be used on existing MRIs with a simple software upgrade.

“We developed a novel HR-DWI optimized for prostate imaging that improves image quality and resolution, yielding better sensitivity for detecting low-volume prostate cancers typically observed in active surveillance patients,” the researchers said.

Source: Sharif-Afshar AR, Nguyen C, Feng T, et al. Prospective pilot study of a novel high-resolution diffusion-weighted prostate MRI. Abstract of a poster presented at the 91st Annual Meeting of the Western Section of the American Urological Association, Indian Wells, California, October 25, 2015.