The ability to conduct ‘partial field of view’ scans in QT ultrasound transmission ultrasound is investigated. The standard tomographic data acquisition is typically conducted in a full 360 degree aperture, which may limit the possibility of real time intervention and/or patient positioning for medical imaging. Transmission ultrasound has many advantages over other imaging modalities such as, it does not emit ionizing radiation, does not require contrast agent, etc. A partial field of view data acquisition in this context is therefore attractive. Three scenarios are investigated: breast, whole body, and orthopedic imaging. A full suite of 180 views at 2 degree intervals and 192 mm in the vertical direction was collected from the QT ultrasound™ scanner in the orthopedic and whole body scenarios. The vertical extent of the breast image varied with breast size. Subsequent reconstructions were carried out with a subset of the views incorporated. The contiguous sector of missing angles varied from 8, 16, 32, 40, 60 and 92 degrees. The difference between the corresponding images was quantitatively and qualitatively analyzed and compared. It was found that a large lacuna (gap) of contiguous data did not significantly (clinically) degrade image quality, and the quantitative values, where relevant. The open acquisition scenario allows us to carry out medical intervention as well as potentially decrease patient anxiety. The quantitative nature of the degradation is noted and correlated with the missing sector angles for clinical scenarios, and the implications discussed.
There is a need to provide better imaging methods for infants as there are few good options. CT can provide reasonable image quality with limited soft tissue contrast at a cost of large radiation dose. MRI can provide better soft tissue contrast, but the small size of an infant produces poor signal to noise and thus long scan times. Both types require anesthesia, which carries a substantial mortality risk for young patients and especially sick ones. Ultrasound imaging has been principally relegated to relatively simple applications in in orthopedics and diagnostics due to the inability to achieve high resolution at depth in complex structures. Quantitative Transmission (QT) Ultrasound relies on low frequency information which has greater penetrating power and 3D Inverse Scattering to produce high resolution and contrast at substantial depth. We built a prototype device for imaging small animals and tested the performance on 7-10lb piglets to simulate the conditions necessary to scan a newborn infant human. Image acquisition was entirely conventional with the currently available QT ultrasound breast imagers, but reconstruction required significant modification to deal with the additional complexity. We report on the changes in methods as well as the preliminary performance of the system in this configuration.
The challenge of ultrasound tomography in the presence of high impedance contrast is well known. We have successfully used full 3D transmission inverse scattering and refraction corrected reflection tomography to create 3D high-resolution images of the human breast. However, these tissues do not encompass the high contrast that occurs in orthopaedics scenarios, such as the human knee, where cranial and trabecular bone are present. Even though the high contrast of the bone is problematic for model based iterative reconstruction methods, we successfully image the tissue near, and in, the Femur-Tibia (F-T) space using an adapted QT Ultrasound Scanner and adapted inverse scattering algorithm.
We show preliminary reconstructions of a cadaver knee that indicates that we can quantitatively and accurately image proximal soft tissue structures. We give correlations between MR images and QT Ultrasound transmission images that show correlation with known structures: besides the femur, tibia, and fibula, we see the condyle structures (medial and lateral), medial and lateral menisci internal to the F-T space, collateral ligaments, infrapatellar fat pad (Hoffa’s pad), patellar ligament, and various ligaments, tendons and musculature in the leg above and below the knee.
We establish that a substantially different reconstruction protocol (than that of the breast) for 3D inverse scattering is required to obtain these images and we discuss the implications of these changes. These preliminary results show that high resolution of clinically relevant tissue is feasible with ultrasound tomography even within the F-T space.