Optimal Selection of the Effective Echo Time (TEeff ) for T2-Weighted Fast-Spin-Echo MRI of the Prostate at 3.0 T: Effect on Lesion Conspicuity.

BACKGROUND

Clinical T 2-weighted (T2W) MRI of prostate cancer (PCa) usually implements a 2D fast-spin-echo (FSE) sequence, but understanding the echo-time-dependent contrast behavior is not straightforward due to the complicated FSE signal evolution. Consequently, consensus-based recommendations on the optimal effective echo time (TEeff) to maximize contrast are lacking.

PURPOSE: To investigate the effect of TEeff on PCa lesion contrast in prostate T2W MRI.

STUDY TYPE: Phantom and in vivo prospective study.

SUBJECTS: A standard MRI phantom and 53 prostate cancer patients (29 for image evaluation and 24 for quantitative lesion analysis).

FIELD STRENGTH AND SEQUENCE: Multi-slice T2W FSE sequence at 3 T acquired at multiple TEeff values.

ASSESSMENT: Three readers (13, 25, and 27 years' experience) evaluated TEeff = 100 ms versus 150 ms on diagnostic quality and reader preference. The effective T 2 relaxation rates (T 2,eff) were measured using FSE sequences in the phantom and used to predict the optimal TEeff maximizing T2W contrasts. From multi-TEeff scans of subjects with suspected PCa, T 2,eff values of PCa lesions and healthy tissue were measured and used to calculate the optimal TEeff maximizing the lesion contrast. In vivo contrast metrics were measured as a function of TEeff.

STATISTICAL TESTS: Wilcoxon test of reader scores, with p < 0.05 defining statistical significance.

RESULTS

No statistically significant difference was found in diagnostic quality between TEeff = 150 ms and 100 ms images, but all three readers significantly favored TEeff = 150 ms. Phantom experiments demonstrated that TEeff-dependent FSE signal progression can be characterized by T 2,eff values typically 40% longer than actual T 2 values, allowing accurate prediction of optimal TEeff within 2%-5%. Applied to PCa imaging, in vivo measurements indicated that effective T 2 relaxation times of the prostate are on average 1.5× longer than published T 2 values.

DATA

CONCLUSION

The benefits of TEeff = 150 ms versus 100 ms in prostate T2W FSE were supported by reader preference, phantom experiments, in vivo measurements, and analytic optimizations.

EVIDENCE LEVEL: 2.

TECHNICAL EFFICACY: 2.