Piotr Kozlowski, PhD

Vancouver, British Columbia, Canada—The sensitivity of several MRI techniques in diagnosing prostate cancer is problematic, but two techniques, diffusion-weighted (DW) and dynamic contrast-enhanced (DCE) MRI, appear promising.

Researchers at the Vancouver Prostate Center, British Columbia, are the first in the world to study combined DW and DCE. In a recent pilot study, they found that the sensitivity of the two imaging techniques combined was greater than that of each of the individual techniques.

"DW has, in the past, been fairly difficult, technically, to use as it had low sensitivity and was very sensitive to any movement by the patient," explained lead author Piotr Kozlowski, PhD, a research scientist and assistant professor of surgery at the Prostate Center.

However, recent advances in MRI equipment have significantly improved the accuracy and sensitivity of the technique, he said.

"The whole idea of this project is that we can eliminate histology for diagnostic testing for prostate cancer," said Dr. Kozlowski, who presented the study's findings at the AUA Western Section annual meeting here.

"Pathology, right now, is the gold standard, but the problem is that you don't really know exactly which tissue is normal and which is not unless you remove the whole gland, which doesn't happen very often. Biopsies are usually taken from very specific regions of the prostate gland, so if it turns out that there is a tumor somewhere between the two sides, you won't be able to see it."

"By applying very specific imaging methods, you may be able to get results that are as good or better than pathology results," said Dr. Kozlowski, adding that the noninvasive nature of MRI is also a key advantage.

Sensitivity tested

In the study, 14 patients with elevated PSA and/or a prostate nodule, none of whom had received previous treatment, underwent MRI examinations with a Signa Horizon 1.5T clinical scanner (General Electric Healthcare, Milwaukee) before undergoing transrectal ultrasound-guided biopsies. Ten axial slices, 5 mm each, were imaged across the prostate gland for DW and DCE data.

Average apparent diffusion coefficient (ADC) values were calculated on the hypointense areas in the scanned maps. Average values for DCE parameters—K^trans, extravascular extracellular space, maximum concentration of Gd-DTPA, maximum enhancement, onset time, and mean gradient and transfer constant—were calculated from the fast-enhancing areas in Gd-DTPA concentration maps.

Control ADC and DCE parameter values were derived from the areas of the prostate deemed normal on the basis of MRI and histology results. Correlation with histology considered the results of both the biopsy and the prostatectomy. Then histology and MRI data were mapped into standard octant biopsy maps, and the differences between tumor, normal peripheral zone, and normal central gland were analyzed using a Tukey-Kramer test.

Average values of all parameters except the extravascular extracellular space showed significant differences between tumor and normal prostate. ADC alone demonstrated 54% sensitivity and 100% specificity, while DCE showed 59% sensitivity and 74% specificity. When combined, sensitivity improved to 87%, although specificity dipped slightly, to 74%. Translated to the clinical realm, 10 of 14 biopsies read positive for prostate cancer, and eight of the 10 patients subsequently underwent radical prostatectomy.

"The specificity of the DCE technique is lower than DW, probably because glandular BPH will show some degree of contrast enhancement," Dr. Kozlowski explained. "When combined, the sensitivity increases significantly, which strongly suggests that both techniques provide comparable information regarding structure and histology of the prostate tissue. We are trying to find the best possible parameters to distinguish normal tissue from cancerous tissue.

"Detecting cancer is not the whole thing; we want to find out if we can correlate the parameters from our MRI data with tumor grade and estimate tumor volume."

Dr. Kozlowski and his colleagues are now planning a larger study with patients representing a wide spectrum of tumor grades. Data collection is expected to begin late in 2005.