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