Accuracy of Diffusion Weighted Images and MR Spectroscopy in Prostate Lesions – Our Experience with Endorectal Coil on 1.5 T MRI

Abstract

Introduction: Prostatic cancer is most commonly seen in individuals greater than 65 years of age. The incidence rates are constantly increasing. Aim: To assess the accuracy of the non-contrast sequences {Diffusion Weighted Imaging (DWI) and Magnetic Resonance Spectroscopy (MRS)} in the multiparametric Magnetic Resonance Imaging (mp-MRI) in identifying and differentiating benign and malignant prostate lesions using endorectal coil on 1.5 T MRI. Materials and Methods: Twenty-six patients with clinical indications for prostate lesions were evaluated using endorectal coil on 1.5 T MRI. DWI and MRS were obtained in all the lesions. Signal change on T2 weighted images, Apparent Diffusion Coefficient (ADC) values and choline + creatinine to citrate ratios (Cho+Cr/Ci) of the lesions were obtained for all the patients. All the patients underwent Transrectal Ultrasound (TRUS) guided biopsy within one week of MRI study. Signal change on T2 weighted images, DWI and Cho+Cr/Ci ratios were correlated with the histopathological findings using appropriate statistical analysis (Wilson score). Results: Of the 26 patients, seven had benign pathology and 19 had malignant pathology on the histopathological examination. Sensitivity and specificity (89.5% and 85.7% respectively) of the diagnosis of malignancy based on DWI were quite good. Positive and negative predictive values were also very much acceptable (94.4% and 75% respectively). Though, MRS had good sensitivity and Positive Predictive Value (PPV) (84.2% and 76.2% respectively), specificity and Negative Predictive Value (NPV) were poor (28.6% and 40% respectively). Accuracy of imaging diagnosis based on combining T2, DWI and MRS was same as that of results based on T2 signal alone (80.8%) and had higher sensitivity and lower specificity than DWI alone (94.7% and 42.9% respectively). Receiver Operating Characteristic (ROC) curves were calculated for ADC values and Cho+Cr/Ci ratios. The Area Under the Curve (AUC) for ADC is 0.74 and for Cho+Cr/Ci is 0.70. Conclusion: Comparing the accuracy of the non-contrast sequences T2, DWI and MRS in identifying and differentiating benign and malignant lesions, giving weightage to the MRS in mp–MRI reduces the negative predictive value. The diagnosis of malignancy based on diffusion restriction was quite good and it can be the workhorse for prostate cancer detection as a shortened mp-MRI.

Keywords

• benign
• cancer
• multiparametric magnetic resonance imaging