Cutting Edge Urology

T his PDF belongs to matthew.hooson@springer.co 36 • CUTTING EDGE - UROLOGY Elastic registration allows deformation, warping, and dimensional changes between images, based on mathematical algorithms. As every prostate is different in density and elasticity, these calculations are estimations. Rigid registration permits only rotational and translational varia- tions between images, without changing the images themselves. The urologist needs to make some adjustments in case of error due to the rigid registration, using manual correction of the alignment and targeting or using different degrees of pressure/insertion depth of the US probe (Fig. 3) [19]. While overlapped images obtained from rigid registration usually have discontinuous borders looking less pleasant to the eye than elastic registration, it is difficult to define which method is able to achieve better accuracy. Elastic registration should guarantee better matching, but some experts think the cognitive adjustment might overcome the issues encountered with rigid regis- tration and allow better spatial precision, especially in patients having unusual gland dimensions. Fusion Platforms MRI/US fusion software-based targeted biopsy first of all requires a diagnostic mp-MRI with a report scheduling all the suspicious lesions edited by an expert uro-radiologist (Fig. 4). mp-MRI images are loaded in the specific software and regions of interest are then outlined. The patient is positioned, and a TRUS is performed, with MR images superimposed on real-time US images (Fig. 5). Targeted biopsies directed to mp-MRI-suspicious lesions are then performed (Figs. 6 and 7). A standardized report of the biopsy session should be provided, including a detailed notifica- tion of MRI/US fusion software-based targeted biopsies, and eventually standard biopsies, that were performed. It can be done in the same manner as for mp-MRI, using a standardized diagram of the prostate, including drawings of the sampled lesions. The report must underline how good the MRI/US fusion software-based targeted biopsy matched the mp-MRI one (e.g., visibility of the lesion). All this information will be useful for analyzing the final histopathology results (Fig. 8). Fig. 3: Elastic and rigid methods to register MR images to live TRUS. ( a ) MRI/US registration with minimal US- probe deformation and use of an endorectal coil (ERC) for MRI; ( b ) MRI/US registration with increased manual US- probe deformation that can mimic ERC deformation. In middle images in ( a ) and ( b ) is shown the simple overlap of US and MR images, resulting in reduced correlation between imaging modalities. Rigid registration permits only rotational and translational variations between images. Elastic registration allows local deformation, e.g., caused by an endorectal coil or TRUS probe. ERC endorectal coil (Reproduced from Logan et al . [19]). Cutting EDGE_Urology(SUN)_final.indd 36 27-Mar-18 10:00:30 AM