Aritrick Chatterjee^{1}, Dianning He^{1,2}, Xiaobing Fan^{1}, Tatjana Antic^{3}, Ajit Devaraj^{4}, Yulei Jiang ^{1}, Gregory S Karczmar^{1}, and Aytekin Oto^{1}

This study develops a new tool that estimates the risk map for prostate cancer using quantitative mpMRI metrics and investigates the feasibility of this tool in screening for PCa. Quantitative mpMRI parameters: ADC, T2 and DCE signal enchantment values were calculated and subsequently cancer presence was predicted based on estimated risk scores. The sensitivity, specificity, positive predictive value and negative predictive value for PCa detection using a sector based analysis were 75.0%, 88.6%, 84.7% and 80.8% respectively. The area under the curve in ROC analysis was 0.818. Importantly, all the index lesions were identified by the risk map tool.

Patients (*n*=22) with histologically confirmed PCa underwent preoperative prostate mpMRI on 3T Philips Achieva scanner using a 6-channel cardiac phased array coil placed around the pelvis combined with an endorectal coil (Medrad, Bayer Healthcare) prior to undergoing radical prostatectomy. The protocol included T2-weighted (T2W), multi-echo T2-weighted, diffusion weighted and dynamic contrast enhanced (DCE) images (see Table 1). Quantitative mpMRI metrics: ADC, T2, signal enhancement rate (α) from DCE were calculated on a voxel-by-voxel basis for the whole prostate. A custom MATLAB software co-registered these three maps to T2-weighted images matching the resolution, FOV, slice thickness, etc. The whole prostate and central gland (CG) were marked by a radiologist. A normalized risk value (0-100) for each mpMRI parameters were obtained with high risk values associated with low T2 and ADC, and high α.

ADC Risk score = 100 × (maximum_ADC – voxel_ADC) / maximum_ADC [1]

T2 Risk score = 100 × (maximum_T2 – voxel_T2) / maximum_T2 [2]

DCE Risk score = 100 × voxel_α / maximum_α [3]

where maximum_ADC = 3.0 µm^{2}/ms, maximum_T2 = 250 msec and maximum_α = 10% per sec, and voxel_ADC, voxel_T2 and voxel_ α are the ADC, T2 and α values for the voxel for which the risk is estimated.

Since, CG is a region that typically has false positives on DCE due to high α (similar to PCa), the DCE risk scores are halved. The final risk map which is a weighted sum of the risk scores (ADC 40%, T2 40%, DCE 20%) is displayed. Five patients were used as test set to find the threshold for predicting PCa using Youden’s index from ROC analysis and visual inspection of a radiologist. In the subsequent 17 patients, any voxel with risk score above the threshold final risk score was considered cancer. The final predicted PCa map was displayed after using a filter where any region with a minimum of 30 conjoint voxels (~4.8 mm^{2}) was predicted to be a cancer lesion. Each prostate was divided into 18 sectors: 6 sectors each (CG, anterior and posterior peripheral zones in the left and right) in apex, mid and base of the prostate. A sector based analysis was performed by matching prostatectomy verified malignancy and PCa predicted by the risk analysis tool. In addition, the sensitivity for detecting the index lesion was also calculated.

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