Imaging of Total Ankle Arthroplasty: Normal Imaging Findings and Hardware Complications.

End-stage ankle osteoarthritis often significantly impacts patients' quality of life. This can be managed surgically either by ankle arthrodesis or total ankle arthroplasty (TAA). Although ankle arthrodesis is considered by some as the standard-of-care surgical option for this condition, it restricts range of motion and may lead to accelerated osteoarthritis of neighboring joints. Better understanding of ankle biomechanics, the biological effects of orthopaedic devices, and new surgical techniques have led to significant improvements in the designs of TAAs, and over the last several decades TAA has been used increasingly to treat patients with end-stage tibiotalar osteoarthritis. However, complication and ultimate failure rates remain greater than those seen with total knee and hip arthroplasty, and imaging is often critical in determining whether a prosthesis is beginning to fail. As a result, imagers should be familiar with the basic types of TAAs in clinical use, the normal radiographic appearances, as well as the common complications seen with this procedure.

High-resolution ultrasound of the fascia lata iliac crest attachment: anatomy, pathology, and image-guided treatment.

Pathology of the fascia lata attachment at the iliac crest (FLAIC) is an under-recognized and often misdiagnosed cause of lateral hip pain. The fascia lata has a broad attachment at the lateral iliac crest with contributions from the tensor fascia lata muscle, the iliotibial band, and the gluteal aponeurosis. The FLAIC is susceptible to overuse injuries, acute traumatic injuries, and degeneration. There is a paucity of literature regarding imaging and image-guided treatment of the FLAIC. We review anatomy and pathology of the FLAIC, presenting novel high-resolution (18-24 MHz) ultrasound images including ultrasound guidance for targeted therapeutic treatment.

CT of the Abdomen with Reduced Tube Voltage in Adults: A Practical Approach.

Recent innovations in computed tomographic (CT) hardware and software have allowed implementation of low tube voltage imaging into everyday CT scanning protocols in adults. CT at a low tube voltage setting has many benefits, including (a) radiation dose reduction, which is crucial in young patients and those with chronic medical conditions undergoing serial CT examinations for disease management; and (b) higher contrast enhancement. For the latter, increased attenuation of iodinated contrast material improves the evaluation of hypervascular lesions, vascular structures, intestinal mucosa in patients with bowel disease, and CT urographic images. Additionally, the higher contrast enhancement may provide diagnostic images in patients with renal dysfunction receiving a reduced contrast material load and in patients with suboptimal peripheral intravenous access who require a lower contrast material injection rate. One limitation is that noisier images affect image quality at a low tube voltage setting. The development of denoising algorithms such as iterative reconstruction has made it possible to perform CT at a low tube voltage setting without compromising diagnostic confidence. Other potential pitfalls of low tube voltage CT include (a) photon starvation artifact in larger patients, (b) accentuation of streak artifacts, and (c) alteration of the CT attenuation value, which may affect evaluation of lesions on the basis of conventional enhancement thresholds. CT of the abdomen with a low tube voltage setting is an excellent radiation reduction technique when properly applied to imaging of select patients in the appropriate clinical setting.

Signal detection and location-dependent noise in cone-beam computed tomography using the spatial definition of the Hotelling SNR.

PURPOSE: Quality assurance in computed tomography (CT) is commonly performed with the Fourier-based modulation transfer function (MTF) and the noise variance, while more recently the noise power spectrum (NPS) has increased in popularity. The Fourier-based methods make assumptions such as shift-invariance and cyclostationarity. These assumptions are violated in real clinical systems and consequently are expected to result in systematic errors. A spatial approach, based on the object transfer matrix (T) and the covariance matrix (K) theory, does not require these assumptions and can provide a more general description of the imaging system. In this paper, the authors present an experimental methodology and data treatment for quality assessment of a lab cone-beam CT system by comparing the spatial with the Fourier approach in 2D reconstructed slices. METHODS: In order to have control over all experimental parameters and image reconstruction, a bench-top flat-panel-based cone-beam CT scanner and a cylindrical water-filled poly(methyl methacrylate) (PMMA) phantom were used for the noise measurements. An aluminum foil inserted in the water phantom enabled the estimation of the line response function (LRF) with a limited number of assumptions. The authors evaluated the spatial blur, the noise and the signal-to-noise ratio (SNR) using the spatial approach as well as the Fourier-based approach. In order to evaluate the degree of noise nonstationarity of their cone-beam CT system, the authors evaluated both the local and global CT noise properties and compared them using both approaches. RESULTS: For the laboratory cone-beam CT, the location-dependent noise evaluation showed that in addition to the noise variance, the NPS and covariance eigenvector symmetry depend on the location in the image. The estimated signal transfer was similar for both approaches. Unlike the Fourier approach which uses the same exponential wave function basis for both MTF and NPS, the eigenvectors of T and K were significantly different. CONCLUSIONS: By using the eigenvectors of the noise and object transfer to characterize the system, the spatial approach provides additional information to the Fourier approach and is therefore an important tool for a thorough understanding of a CT system.