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Table 4 Overview of advanced MRI-based techniques for prostate imaging

From: Evolution of prostate MRI: from multiparametric standard to less-is-better and different-is better strategies

Type of advanced imaging [reference] Goals Derived parameters Promising achievements
Intravoxel incoherent motion (IVIM) [54] • To use a biexponential model for separating pure water molecule diffusion from perfusion-related diffusion linked to capillary microcirculation • Apparent diffusion coefficient (ADC)
• Pure molecular diffusion (D)
• Perfusion-related parameters such as D* and f
• Increased accuracy in detecting PCa compared to the mono-exponential model, though with no added value in the TZ
• Differentiation of high-grade versus low-grade tumours, especially when using D
Diffusional kurtosis imaging (DKI) [52, 54] • To account for non-Gaussian distribution of water molecules motion due to heterogeneous microenvironments with many or large interfaces (e.g., intracellular structures and organelles)
• To better exploit tissue microstructural complexity
• To better represent water diffusion within the intracellular compartment, and in turn better represent tissue cellularity
• Diffusion coefficient Dapp (corrected for observed non-Gaussianity)
• Apparent diffusional kurtosis Kapp (a dimensionless measure of the deviation of tissue diffusion from a Gaussian pattern)
• Better than DWI in assessing PCa and in differentiating low- versus high-grade tumours
Diffusion tensor imaging (DTI) [56] • To account for the degree of anisotropy affecting water diffusion • ADC
• Fractional anisotropy
• DTI tractography
• Correlation with tumour aggressiveness and tissue composition
Restriction spectrum imaging (RSI) [57] • To collect diffusion data with multiple gradient directions and b values, in association with a linear mixture model to resolve a spectrum of length scales, and acquisition of geometric information
• To separate intracellular from extracellular signal, and in turn better reflect tissue cellularity
• To account for underlying geometry information
• RSI cellularity index • Added value compared to mpMRI in detecting PCa
• Close correlation with Gleason score
• Correcting for geometric distortion in targeted biopsy of small volume lesions
• RSI has the potential to be normalised in a machine- and technique-independent way
Quantitative dynamic contrast-enhanced (DCE) imaging [58, 59] • Deriving quantitative parameters to describe tissue vascularisation and blood flow in the normal prostate or PCa They depend on the pharmacokinetic model used. Examples:
• Transfer constant (Ktrans): exchange constant between blood plasma and extravascular extracellular space
• Rate constant (Kep): exchange constant between extravascular extracellular space and blood plasma
• Improving cancer detection, localisation, and staging
• Assessment of biological aggressiveness and prognosis
• Increased sensitivity for recurrent cancer after radiation therapy, radical prostatectomy, or high-intensity-focused ultrasound
• Monitoring the effects of hormone therapy or antiangiogenic drugs
Radiomics [60] • To extract quantitative information from medical images (statistics, metrics, descriptors), thus accounting for biological heterogeneity of disease A large variety of features describing:
• Intensity
• Texture
• Shape
• Automatic or semiautomatic segmentation of the prostate for radiation therapy planning, biopsy preparation, volume estimation, and PCa localisation
• Detection and risk stratification in active surveillance
• Pathological grade prediction
• Identification of biologically relevant targets for biopsy
• Radiogenomics
PET/MRI [53] • To combine superior soft tissue contrast of MRI with panoramic biologic information from PET A variety of radiotracers are used in PET/MRI, including:
• [18F]-NaF for bone metastatic disease
• [11C]-choline for recurrent disease
• [68Ga]-PSMA-HBED-CC (for staging, recurrence, and treatment response assessment)
• Improved diagnosis compared to MRI alone
• Improved accuracy in detecting and characterising bone disease compared to PET/CT
• Improved detection of local recurrence compared to PET/CT alone
  1. ADC apparent diffusion coefficient, CT computed tomography, D diffusion, DTI diffusion tensor imaging, DWI diffusion-weighted imaging, mpMRI multiparametric MRI, MRI magnetic resonance imaging, PCa prostate cancer, PET positron emission tomography, PSMA prostate-specific membrane antigen, RSI restriction spectrum imaging, TZ transition zone