A statistical model-based technique for accounting for prostate gland deformation in endorectal coil-based MR imaging

Multimodal image registration for the identification of dominant intraprostatic lesion in high-precision radiotherapy treatments

PURPOSE

The integration of CT and multiparametric MRI (mpMRI) is a challenging task in high-precision radiotherapy for prostate cancer. A simple methodology for multimodal deformable image registration (DIR) of prostate cancer patients is presented.

METHODS

CT and mpMRI of 10 patients were considered. Organs at risk and prostate were contoured on both scans. The dominant intraprostatic lesion was additionally delineated on MRI. After a preliminary rigid image registration, the voxel intensity of all the segmented structures in both scans except the prostate was increased by a specific amount (a constant additional value, A), in order to enhance the contrast of the main organs influencing its position and shape. 70 couples of scans were obtained by varying A from 0 to 800 and they were subsequently non-rigidly registered. Quantities derived from image analysis and contour statistics were considered for the tuning of the best performing A.

RESULTS

A = 200 resulted the minimum enhancement value required to obtain statistically significant superior registration results. Mean centre of mass distance between corresponding structures decreases from 7.4 mm in rigid registration to 5.3 mm in DIR without enhancement (DIR-0) and to 2.7 mm in DIR with A = 200 (DIR-200). Mean contour distance was 2.5, 1.9 and 0.67 mm in rigid registration, DIR-0 and DIR-200, respectively. In DIR-200 mean contours overlap increases of +13 and +24% with respect to DIR-0 and rigid registration, respectively.

CONCLUSION

Contour propagation according to the vector field resulting from DIR-200 allows the delineation of dominant intraprostatic lesion on CT scan and its use for high-precision radiotherapy treatment planning. Advances in knowledge: We investigated the application of a B-spline, mutual information-based multimodal DIR coupled with a simple, patient-unspecific but efficient contrast enhancement procedure in the pelvic body area, thus obtaining a robust and accurate methodology to transfer the functional information deriving from mpMRI onto a planning CT reference volume.

Performance comparison of 1.5-T endorectal coil MRI with 3.0-T nonendorectal coil MRI in patients with prostate cancer

RATIONALE AND OBJECTIVES

To compare prostate morphology, image quality, and diagnostic performance of 1.5-T endorectal coil magnetic resonance (MR) imaging (MRI) and 3.0-T nonendorectal coil MRI in patients with prostate cancer.

MATERIALS AND METHODS

MR images obtained of 83 patients with prostate cancer using 1.5-T MRI systems with an endorectal coil were compared to images collected from 83 patients with a 3.0-T MRI system. Prostate diameters were measured, and image quality was evaluated by one American Board of Radiology (ABR)-certified radiologist (reader 1) and one ABR-certified diagnostic medical physicist (reader 2). The likelihood of the presence of peripheral zone cancer in each sextant and local extent was rated and compared to histopathologic findings.

RESULTS

Prostate anterior-posterior diameter measured by both readers was significantly shorter with 1.5-T endorectal MRI than with 3.0-T MRI. The overall image quality score difference was significant only for reader 1. Both readers found that the two MRI systems provided a similar diagnostic accuracy in cancer localization, extraprostatic extension, and seminal vesicle involvement.

CONCLUSIONS

Nonendorectal coil 3.0-T MRI provides prostate images that are natural in shape and that have comparable image quality to those obtained at 1.5 T with an endorectal coil, but not superior diagnostic performance. These findings suggest an opportunity exists for improving technical aspects of the 3.0-T prostate MRI.