Three‐dimensional balanced steady state free precession imaging of the prostate: Flip angle dependency of the signal based on a two component T2‐decay model

Abstract

Purpose: To investigate the contrast of three-dimensional balanced steady state free precession (3D bSSFP) in the two component T2 model and to apply the results to optimize 3D bSSFP for prostate imaging at 1.5 Tesla. Materials and Methods:In each of seven healthy volunteers, six 3D bSSFP acquisitions were performed with flip angles (a) equally spaced between 10 and 110 . Predictions of signal and contrast were obtained from synthetic bSSFP images calculated from relaxation parameters obtained from a multi-spin-echo acquisition. One biexponential and two monoexponential models were applied. Measured and predicted signals were compared by simple linear regression. Results:The measured contrast to signal ratio increased continuously with a. Mean R 2 for the biexponential model was almost constant for a in the range 50-110 . The biexponential model was a better predictor of the measured signal than the monoexponential model. A monoexponential model restricted to the echoes TE ¼ 50-125 ms performed similar to the biexponential model. The predicted contrast peaked at a between 50 and 90 .Conclusion: Prostate imaging with bSSFP benefited from high flip angles. The biexponential model provided good signal prediction while predictions from the monoexponential models are dependent on the range of TE used for T2 determination. IN PROSTATE IMAGING, anatomical details are excellently depicted by MRI using T2-weighted rapid acquisition with relaxation enhancement (RARE) (also known as T2W-TSE or T2W-FSE), which has been the gold standard (1,2).Diagnostic performance has improved as new technological developments such as endorectal coil imaging and increasing field strengths has allowed for imaging at higher resolutions (2-4). The T2W-RARE applies a 2D sampling regime. Hence, imaging is constrained to relatively thick (>3 mm) slices. The diagnostic performance is expected to improve if throughplane image resolution is increased. To achieve thinner slices, a 3D sampling regimen is required. Ikonen et al (5) demonstrated thin-slice (1.5 mm) prostate imaging by applying the 3D dual-echo steady state (DESS) (6) technique. Further improvements in resolution may be gained by applying the simpler and more time-efficient balanced steady state free precession (bSSFP) sequence also known as balanced FFE, TrueFISP,. This technique is ideal for 3D scanning because it may be implemented with very short repetition time (TR) without loss of signal.The contrast of bSSFP has been thoroughly described (7-9). It is dependent on the tissue T2/T1-ratio, flip angle, and resonance offset. It has been shown that T2 decay in prostate tissue is of biexponential nature (10,11). The bSSFP signal may be predicted based on the results of the two component model. This presumably provides a more accurate tool for sequence optimization than the use of the monoexponential model.The aim of this work was to investigate the contrast of 3D bSSFP in the light of a two component T2 model and to apply the results to optimize high resolution 3D bSSFP for prostate im...

Luminal Water Imaging: A New MR Imaging T2 Mapping Technique for Prostate Cancer Diagnosis

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