Electromagnetic tracking-based ultrasound/computed tomography fusion imaging in dogs: preliminary application to ocular and periocular regions

In ultrasound/computed tomography (CT) fusion images, ultrasound allows visualization of the target in real time. CT provides a navigation for ultrasound scanning and improves the overview in areas of limited visualization with ultrasound. This study was performed to investigate the feasibility of ultrasound/CT fusion based on an electromagnetic tracking technique using external fiducial markers for canine ocular and periocular regions. In 7 Beagle dogs, contrast-enhanced CT images of the head were obtained with placing external fiducial markers over the frontal region and both sides of the forepaws of the dog. Ultrasonography was performed under a magnetic field by installing a position sensor in the linear probe, without changing the dog's position. The positions of the external fiducial markers were adjusted and matched, based on the CT images. The execution time of co-registration and the distance between the regions of interest and the co-registration points, the frontal bone, cornea, retina, and optic nerve, were estimated. Approximately 60% of external fiducial markers were properly recognized in all dogs. After adjustment, all external fiducial markers were precisely matched. The co-registration execution time was less than 1 min. The distances between the regions of interest and co-registration points were less than 3 mm in all dogs. The electromagnetic tracking technique using external fiducial markers was a simple and applicable method for fusion imaging of a canine head using real-time ultrasonography and CT. This technique can be useful for interventional procedures of retrobulbar and periorbital lesions.

Clinical utility of SPECT-CT co-registration imaging

The interpretation of nuclear medicine studies is largely based on function. However, this interpretation becomes more accurate and reliable when there is a corresponding precise anatomical localization. Hybrid systems are opening up a new era in SPECT imaging. A tertiary hospital in the Philippines has acquired the country's first hybrid imaging device combining a dual-detector, variable angle gamma camera with a low dose X-ray tube attached to the same gantry. This study evaluates the clinical utility of a hybrid imaging system, SPECT/CT for functional mapping with selected radiotracers. SPECT data were first interpreted alone and then re-assessed with the addition of SPECT/CT co-registered images. Patients referred for various nuclear medicine procedures with SPECT components in the first six months of operation studied for various clinical situations were evaluated in the study. Our study included sixty-four (64) patients in the first year of operation of SPECT/CT co-registered imaging systems. This included 23 with I-131, six with sulfur colloid, four with Gallium 67, five with Tc99m Sestamibi and 26 with Tc99m HOP. The pathologic sites in 28 out of 64 (44 percent) patients were noted in both SPECT and SPECT/CT co-registered images. Additionally, SPECT/CT co-registered images provided the precise anatomical localization in 12 (19 percent) patients not clearly evident in SPECT images alone and enabled the exclusion of disease in sites of physiologic tracer deposition in 16 (25 percent) patients found suspicious in SPECT alone leading to a change in the therapeutic approach. SPECT/CT allows a more precise interpretation of scintigraphic studies using selected radiotracers for various clinical situations. It provides additional information that improves diagnostic accuracy of SPECT and impacts on patient management indicating that SPECT/CT co-registered systems are suited for routine use in clinical practice.