Rationale and Objectives: The study goal was to test whether the improved accuracy in quantitative dynamic contrast-enhanced magnetic resonance imaging measurement using a point-of-care portable perfusion phantom (P4) leads to better stratification of prostate cancer grade. Materials and Methods: A prospective clinical study was conducted recruiting 44 patients scheduled for multi-parameter MRI prostate exams. All participants were imaged with the P4 placed under their pelvic regions. Tissue sampling was carried out for 25 patients at 22 ± 18 (mean ± SD) days after multi-parameter MRI. On histologic examination, a total of 31 lesions were confirmed as prostate cancer. Tumors were classified into low grade (n = 14), intermediate grade (n = 10), and high grade (n = 7). Tumor perfusion was assessed by volume transfer constant, Ktrans, before and after P4-based error correction, and the Ktrans of low, intermediate and high-grade tumors were statistically compared. Results: After P4-based error correction, the Ktrans of low, intermediate, and high-grade tumors were 0.109 ± 0.026 min−1 (95% CI: 0.0094 to 0.124 min−1), 0.163 ± 0.049 min−1 (95% CI: 0.129 to 0.198 min−1) and 0.356 ± 0.156 min−1 (95% CI: 0.215 to 0.495 min−1), respectively, with statistically significant difference among the groups (low vs intermediate: p = 0.002; intermediate vs high: p = 0.002; low vs high: p < 0.001). The sensitivity and specificity of Ktrans value, 0.14 min−1, to detect the clinically significant prostate cancer were 88% and 93%, respectively, after P4 based error correction, but those before error correction were 88% and 86%, respectively. Conclusion: The P4 allows to reduce errors in quantitative dynamic contrast-enhanced magnetic resonance imaging measurement, enhancing accuracy in stratification of prostate cancer grade.