T2-weighted sagittal image of prostate phantom ( a).
#Trials fusion warp zone 1 registration
Secondary aims included determining whether RE differences exist in the user experience level, the target location or the ultrasound plane between the 2 registration methods. A standard clinical workflow was mimicked with MRI acquisition, radiologist interpretation, registration on a commercial platform and urologist FBx 20 but controlling for confounding clinical factors. We directly compared rigid and elastic REs in a controlled setting using a phantom model prostate. Additionally, clinical studies introduce additional variables such as tumor heterogeneity, MRI scoring systems, definitions of csPCa, patient inclusion criteria, user experience levels and different FBx systems such as differences in elastic registration algorithms. Studies performed under experimental conditions are well controlled but lack realism while clinical studies often lack final pathology results for comparison. 14– 19 Experimental and clinical studies have some limitations. Prior groups have compared elastic and rigid registration in the experimental or clinical settings with conflicting results. With an elastic registration framework these pins would be connected by an elastic rubber band, allowing them to deviate from the original configuration and deform to best fit the set of holes. Under a rigid registration framework these pins would be connected by a stiff and rigid material, forcing them to move in unison. While there are several different elastic registration algorithms, 13 conceptually one can think of the general process as a set of connected pins (segmented features on MRI) being inserted in a corresponding set of holes (segmented features on US). This is done to maximize fusion image alignment and create what seems like a more precise depiction of the lesion superimposed on US but it may in fact warp or distort the true anatomy in the process.
#Trials fusion warp zone 1 software
5, 8– 12 The user may still rotate or translate the rigid images initially to create alignment but after elastic transformation is applied the semiautomated software algorithm is permitted to stretch and deform the segmented margin of the MRI to better fit the segmented real-time US margin or vice depending on the platform. In contrast, elastic registration uses a software algorithm to compensate for changes in the segmented prostate shape, which may occur between the pre-procedural MRI and initial or subsequent intraprocedural imaging during the FBx procedure. However, rigid registration maintains the true patient anatomy detected on MRI. This is the simplest method as is does not accommodate deformation of the prostate gland. Rigid registration enables the user to manually rotate and translate the MRI and US images with respect to each other to produce the best global alignment between the images, although the images themselves do not change. 7Ĭommercial FBx platforms can use different methods of registration (rigid or elastic) to fuse MRI data with US. 6 While it is often time-consuming, proper registration and fusion of images are necessary since small targeting errors in the range of 1 to 2 mm may result in missing a visualized csPCa. 4, 5 Registration is the often tedious process of bringing separate imaging modalities (MRI and US) into spatial alignment for ease of viewing, either side by side or blended on top of each other using fusion software. 1– 3 FBx combines the benefits of MRI (high spatial resolution and pre-identified suspicious lesions) with the versatility of US (high temporal resolution) in an outpatient setting. M AGNETIC resonance imaging and commercially available software assisted MRI/US FBx platforms have increased the detection of csPCa while simultaneously decreasing the diagnosis of indolent disease.
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