Piotr Slomka

Variability and accuracy of measurements of prostate brachytherapy seed position in vitro using three-dimensional ultrasound: an intra- and inter-observer study.

This paper is a step in investigating whether three-dimensional (3D) ultrasound can be used intraoperatively to replace Computed Tomography (CT) for localization of brachytherapy seeds. In order to quantify the accuracy and variability of seed localization without introducing effects due to tissues, we first report our results with test phantoms. An inter- and intra-observer study was performed to assess the variability of 2 3D ultrasound scan acquisition methods: Tilt 3D scanning and pull-back 3D scanning. Seven observers measured the positions of gold seed markers in an agar phantom twice in each of the three orthogonal image planes. An analysis of variance (ANOVA) was performed to determine the intra- and inter-observer standard errors of measurement (SEM) and the minimum detectable changes in marker position (deltap). Average intra- and inter-observer SEMs for the tilt scan 3D image were 0.36 and 0.40 mm, respectively. Measurements of the pull-back scan 3D image yielded average intra- and inter-observer SEM of 0.46 and 0.49 mm, respectively. A paired difference analysis showed that the lower SEM for the tilt 3D scan image were statistically significant at a significance level of alpha= 0.05. The accuracy of the US measurements was tested by determining marker coordinates from CT images of the phantom in a stereotactic head frame. CT coordinates were matched to the ultrasound (US) coordinates by means of an affine transform. Average matching errors in x, y, and z were 0.02, 0.10, and -0.02 mm, respectively.

Mixed Reality Merging of Endoscopic Images and 3-D Surfaces

In image-guided neurosurgery, “mixed reality” merging has been used to merge video images with an underlying computer model. We have developed methods to map intra-operative endoscopic video to 3D surfaces derived from pre-operative scans for enhanced visualization during surgery. We acquired CT images of a brain phantom, and digitized endoscopic video images from a tracked neuro-endoscope. Registration of the phantom and CT images was accomplished using markers that could be identified in both spaces. The endoscopic images were corrected for radial lens distortion, and mapped onto surfaces extracted from the CT images via a ray-traced texture-mapping algorithm. The localization accuracy of the endoscope tip was within 1.0 mm. The mapping operation allows the endoscopic images to be permanently painted onto the surfaces. Our method allows panoramic and stereoscopic visualization from arbitrary perspectives (though the original endoscopic video was monoscopic) and navigation of the painted surface after the procedure.

Novel SPECT Technologies and Approaches in Cardiac Imaging

Recent novel approaches in myocardial perfusion single photon emission CT (SPECT) have been facilitated by new dedicated high-efficiency hardware with solid-state detectors and optimized collimators. New protocols include very low-dose (1 mSv) stress-only, two-position imaging to mitigate attenuation artifacts, and simultaneous dual-isotope imaging. Attenuation correction can be performed by specialized low-dose systems or by previously obtained CT coronary calcium scans. Hybrid protocols using CT angiography have been proposed. Image quality improvements have been demonstrated by novel reconstructions and motion correction. Fast SPECT acquisition facilitates dynamic flow and early function measurements. Image processing algorithms have become automated with virtually unsupervised extraction of quantitative imaging variables. This automation facilitates integration with clinical variables derived by machine learning to predict patient outcome or diagnosis. In this review, we describe new imaging protocols made possible by the new hardware developments. We also discuss several novel software approaches for the quantification and interpretation of myocardial perfusion SPECT scans.

Automated Detection of Contractile Abnormalities from Stress-Rest Motion Changes

Changes in myocardial function signatures such as wall motion and thickening are typically computed separately from myocardial perfusion SPECT (MPS) stress and rest studies to assess for stress-induced function abnormalities. The standard approach may suffer from the variability in contour placements and image orientation when subtle changes between stress and rest scans in motion and thickening are being evaluated. We have developed a new measure of regional change of function signature (motion and thickening) computed directly from registered stress and rest gated MPS data. In our novel approach, endocardial surfaces at the end-diastolic and end-systolic frames for stress and rest studies were registered by matching ventricular surfaces. Furthermore, we propose a new global registration method based on finding the optimal rotation for myocardial best ellipsoid fit to minimize the indexing disparities between two surfaces between stress and rest studies. Myocardial stress-rest function changes were computed and normal limits of change were determined as the mean and standard deviation of the training set for each polar sample. Normal limits were utilized to quantify the stress-rest function change for each polar map sample and the accumulated quantified function signature values were used for abnormality assessments in territorial regions. To evaluate the effectiveness of our novel method, we examined the agreements of our results against visual scores for motion change on vessel territorial regions obtained by human experts on a test group with 623 cases and were able to show that our detection method has a improved sensitivity on per vessel territory basis, compared to those obtained by human experts utilizing gated MPS data.