Objectives: Conventional spin-echo (SE) DWI leads to a fundamental trade-off depending on the b value: high b value provides better lesion contrast-to-noise ratio (CNR) by sacrificing signal-to-noise ratio (SNR), image quality, and quantitative reliability. A stimulated-echo (STE) DWI acquisition is evaluated for high-CNR imaging of prostate cancer while maintaining SNR and reliable apparent diffusion coefficient (ADC) mapping.
Methods: In this prospective, IRB-approved study, 27 patients with suspected prostate cancer (PCa) were scanned with three DWI sequences (SE b = 800 s/mm2, SE b = 1500 s/mm2, and STE b = 800 s/mm2) after informed consent was obtained. ROIs were drawn on biopsy-confirmed cancer and non-cancerous tissue to perform quantitative SNR, CNR, and ADC measurements. Qualitative metrics (SNR, CNR, and overall image quality) were evaluated by three experienced radiologists. Metrics were compared pairwise between the three acquisitions using a t test (quantitative metrics) and Wilcoxon rank test (qualitative metrics).
Results: Quantitative measurements showed that STE DWI at b = 800 s/mm2 has significantly better SNR compared to SE DWI at b = 1500 s/mm2 (p < 0.0001) and comparable CNR to high-b value SE DWI at b = 1500 s/mm2 (p < 0.05) in the peripheral zone. Qualitative assessment showed preference to STE b = 800 s/mm2 in SNR and SE b = 1500 s/mm2 in CNR. The overall image quality and lesion detectability among most readers showed no significant preference between STE b = 800 s/mm2 and SE b = 1500 s/mm2. Further, STE DWI had similar ADC contrast between lesion and normal tissue as SE DWI at b = 800 s/mm2 (p = 0.90).
Conclusion: STE DWI has the potential to provide high-SNR, high-CNR imaging of prostate cancer while also enabling reliable ADC mapping.
Key points: • Quantitative analysis showed that STE DWI at b = 800 s/mm2is able to achieve simultaneously high CNR, high SNR, and reliable ADC mapping, compared to SE b = 800 s/mm2and SE b = 1500 s/mm2. • Qualitative assessment by three readers showed that STE DWI at b = 800 s/mm2has significantly higher SNR than SE b = 1500 s/mm2. No preference between SE b = 1500 s/mm2and STE b = 800 s/mm2was determined in terms of CNR with no missed lesions were found in both acquisitions. • A single STE DWI acquisition at moderate b value (800-1000 s/mm2) may provide sufficient image quality and quantitative reliability for prostate cancer imaging within a shorter scan time, in place of two DWI acquisitions (one with moderate b value and one with high b value).
Keywords: Contrast sensitivity; Diffusion MRI; Prostate cancer; Signal-to-noise ratio.