To improve the speed, spatial-resolution and geometric-fidelity of diffusion-weighted imaging in the prostate, and evaluate the possibility of perfusion quantification with multiple b-factors in the same session.Prostate cancer (PCa) is very common and affects approximately one man in every six. DWI is an essential component of PCa diagnosis and staging [1, 2], however, suffers from low resolution, geometric distortions and also low SNR unless signal averaging is employed. Although powerful methods such as multi-coil acceleration can be applied to reduce distortions, this is not practical in the case of prostate imaging with a single, endo-rectal RF coil. A recent accelerated multi-shot acquisition method [3] which is fully compatible with a single coil configuration, exploits the sparsity of diffusion-encoded data in the x-y-k_b-k_d space, where kb and kd are Fourier-transform duals of b and d, the b-factor and the diffusion direction, respectively. It displaces aliasing artefacts toward underused regions of the k_b-k_d plane, and recovers non-aliased signals, at potentially no cost in scan time. The approach shifts sampling along the phase-encoding (PE) direction between b-factors and directions, reducing the number of PE steps for each image but not the total number of images. The acceleration scheme allows for relatively good resolution with good geometrical fidelity in a short scan time and also the acquisition of many b-factors, which may enable perfusion quantification and tumour characterization [4-6].Twelve patients undergoing PCa staging participated in this IRB-approved study (ages: 62±7 years). Imaging was performed at 3 Tesla (MR750w system, GE Healthcare) using an endo-rectal coil (Medrad). T₂-weighted imaging was followed by conventional and accelerated diffusion imaging protocols (Figure 1). For accelerated multi-shot DWI, the segmentation factor equaled the acceleration factor (R=4); thus for each diffusion encoding direction and each b-factor 32 echoes were sampled. Data were reconstructed in the manner introduced in [3], using the magnitude and phase data from a concurrently acquired low-resolution 2D navigator echo (matrix=32x32, TE=128.4ms) for regularization and motion correction, respectively. In order to obtain the highest quality diffusion-weighted images at the diagnostically relevant b-factors 500 and 1400 s/mm² together with a range of b-factors suitable for multi-exponential analysis, a protocol with variable density b-factor sampling was designed. Moreover, to ensure correct diffusion encoding at very low b-factors, a crusher gradient-free design was employed with a minimum b-factor of 12.5 s/mm² for adequate alternate signal crushing. Lesions and normal tissue in the peripheral zone and central gland were delineated on conventional (b=500 and 1400 s/mm²) and accelerated direction-averaged DWI. ADC maps were calculated from non-linear least-square fits with monoexponential functions: $$$S/S_0 = exp(-bD)$$$ using multiple b-factors up to b=500 or b=1400 s/mm² weighted according to the number of averages. Perfusion-free diffusion coefficients (D) and perfusion fractions (f) were calculated in each ROI from non-linear weighted least-square fits with biexponential functions: $$$S/S_0 = (1-f) exp(-bD) + f exp(-bD^*)$$$ [7], using multiple b-factors up to b=500 s/mm² with D* as a free parameter or fixed at 10 mm²/ms.Nine patients had lesions; five had a Prostate Imaging Reporting and Data System (PI-RADS) score of 5, four PI-RADS 4, one PI-RADS 2, and two a PIRADS score of 1. Accelerated DWI produced diagnostic quality high-resolution images (Figs. 2 and 3), except for one case with severe motion. Geometric-fidelity improved by a factor of 2.80 ± 1.99 over conventional DWI (Figure 4). Sample bi-exponential fits are shown in Figure 5: a higher perfusion fraction was found in lesions relative to normal tissue.Scan time for the present accelerated acquisition, with 11 b-factors acquired at two-fold resolution and three-times the geometric-fidelity of a single-shot EPI sequence, was below 6 min. In contrast, acquiring 2 single b-factors and b₀ took nearly 12 min with single-shot EPI. Geometric-fidelity improved nearly as much as the theoretically-expected 3.33-fold. Perfusion parameters were in good agreement with the limited available literature (f: 3.7-23%, D*: 7-21 μm²/ms, D: 1.2-1.9 μm²/ms in [4, 8-10]) and subsequent DCE acquisitions. These improvements were achieved with a single-channel coil and further improvements in accelerated DWI quality may be possible with the addition of multi-channel coils. Future work includes investigating the effect of regularization strength on calculated ADC values [3] and its effect on residual ghosting such as sometimes seen from the rectal wall.Accelerated DWI in the prostate with higher spatial-resolution, geometric-fidelity, and multiple b-factors for potential perfusion quantification within the same session, was feasible while maintaining good SNR and reasonable scan times.