ABSTRACT
The advent of three-dimensional (3D) ultrasound (US) has revolutionized prostate biopsy procedures, allowing for fusion of magnetic resonance imaging (MRI) derived targets with live US resulting in superior detection rates of clinically significant cancers over traditional US-guided biopsies. In this review, we outline the techniques employed to facilitate fusion-guided biopsy and ongoing efforts to address persistent challenges. 3D US volumes of the prostate are obtained in real time by tracking the orientation and location of the US probe while an imaging sweep of the prostate is performed. This positional information is used in combination with various reconstruction algorithms to populate a voxel grid and create a 3D volume of the prostate. Utilizing semi-automated segmentation algorithms, the prostate capsule is delineated and a prior MRI scan is co-registered to the 3D US volume through rigid or elastic registration of the capsule surfaces or mutual information in the image sets. With the MRI registered to the 3D US scan, it is possible for physicians to target MRI identified suspicious lesions under US guidance, thus combining the advantage of the diagnostic capability of MRI and the cost effectiveness of US guidance. Registration accuracy is intrinsic to the success of commercial MRI-US fusion systems for prostate biopsy, and is generally validated through benchtop preclinical studies with prostate mimicking phantoms or clinical studies evaluating cancer detection rates. Ongoing work with sensor-less tracking, fully automated segmentation and registration, and improved imaging quality has the potential to further improve registration accuracy while making 3D US more accessible and convenient for physicians and patients. These efforts will improve diagnostic accuracy which is highly advantageous for determining the appropriate treatment pathway particularly in an era where focal therapy is becoming increasingly accepted.
