Current status of magnetic resonance imaging (MRI) and ultrasonography fusion software platforms for guidance of prostate biopsies

Abstract

Prostate MRI is currently the best diagnostic imaging method for detecting PCa. Magnetic resonance imaging (MRI)/ultrasonography (US) fusion allows the sensitivity and specificity of MRI to be combined with the real-time capabilities of transrectal ultrasonography (TRUS). Multiple approaches and techniques exist for MRI/US fusion and include direct 'in bore' MRI biopsies, cognitive fusion, and MRI/US fusion via software-based image coregistration platforms.

Keywords: MRI/US fusion; MRI/US fusion platforms; prostate MRI; targeted biopsy.

Fig. 1

Images from a 65 year old male with serum PSA 8.7 ng/mL and four previously negative TRUS biopsies who underwent a multiparametric MRI(mpMRI).The axial T2W MR image (A) demonstrates an anterior hypointense lesion in the right apical central gland (yellow asterisk); an ADC map of DW-MRI (B) shows a hypointense focus (yellow asterisk) indicating restricted diffusion; quantitative mapping from DCE-MRI (C) localizes the tumor(yellow box); and MRSI (D) (yellow box) demonstrates an increased choline-to-citrine ratio within the lesion. This patient underwent a MRI/US fusion-guided biopsy following mpMRI demonstrating Gleason 4+4 = 8 (90% in 2 targeted cores) in the right anterior lesion.

Fig. 2

Elastic and Rigid Software Image Registration Methods. Pre-biopsy MR data is registered with real-time TRUS images by aligning landmarks(e.g. points, curves, surfaces,) in corresponding images via rigid or elastic transformations. (A) represents MRI/US registration when there is minimal TRUS deformation and use of an endorectal coil (ERC) for MR images, and (B) demonstrates increased manual TRUS deformation that can mimic ERC deformation. As seen above, a simple overlay of TRUS and MRI models (middle images in panels A and B) results in reduced correlation between imaging modalities. A rigid registration method can account for translational and rotational differences between models while an elastic registration method has the additional ability to account for local deformations (e.g. caused by an endorectal coil or TRUS probe). However, elastic warping can move or alter relative anatomic location despite more matched borders. ERC, endorectal coil.

Fig. 2

Elastic and Rigid Software Image Registration Methods. Pre-biopsy MR data is registered with real-time TRUS images by aligning landmarks(e.g. points, curves, surfaces,) in corresponding images via rigid or elastic transformations. (A) represents MRI/US registration when there is minimal TRUS deformation and use of an endorectal coil (ERC) for MR images, and (B) demonstrates increased manual TRUS deformation that can mimic ERC deformation. As seen above, a simple overlay of TRUS and MRI models (middle images in panels A and B) results in reduced correlation between imaging modalities. A rigid registration method can account for translational and rotational differences between models while an elastic registration method has the additional ability to account for local deformations (e.g. caused by an endorectal coil or TRUS probe). However, elastic warping can move or alter relative anatomic location despite more matched borders. ERC, endorectal coil.