AAPM Task Group Report 261: Comprehensive quality control methodology and management of dental and maxillofacial cone beam computed tomography (CBCT) systems.

Cone-beam computed tomography (CBCT) systems specifically designed and manufactured for dental, maxillofacial imaging (MFI) and otolaryngology (OLR) applications have been commercially available in the United States since 2001 and have been in widespread clinical use since. Until recently, there has been a lack of professional guidance available for medical physicists about how to assess and evaluate the performance of these systems and about the establishment and management of quality control (QC) programs. The owners and users of dental CBCT systems may have only a rudimentary understanding of this technology, including how it differs from conventional multidetector CT (MDCT) in terms of acceptable radiation safety practices.

Practical aspects of functional MRI (NMR Task Group #8).

Functional MR imaging (fMRI) based upon the Blood Oxygen Level Dependent (BOLD) effect is currently an important new tool for understanding basic brain function and specifically allowing the correlation of physiological activity with anatomical location without the use of ionizing radiation. The clinical role of fMRI is still being defined and is the subject of much research activity. In this report we present the underlying physical, technical and mathematical principals of BOLD fMRI along with descriptions of typical applications.

Understanding the process of quantitative ultrasonic tissue characterization.

Because the human vision system cannot distinguish the broad range of gray values that a computer visual system can, computerized image analysis may be used to obtain quantitative information from ultrasonographic (US) real-time B-mode scans. Most quantitative US involves programming an off-line computer to accept, analyze, and display US image data in a way that enhances the detection of changes in small-scale structures and blood flow that occur with disease. Common image textural features used in quantitative US tissue characterization consist of first-order gray-level statistics (eg, occurrence frequency of gray levels independent of location or spatial relationship) and second-order gray-level statistics dependent on location and spatial relationship, including statistical analysis of gradient distribution, co-occurrence matrix, covariance matrix, run-length histogram, and fractal features.

Implementation of a modified birdcage resonator for 19F/1H MRI at low fields (0.14 T).

Fluorine-19 nuclear magnetic resonance of perfluorinated blood substitute materials provides a method for determination of oxygen tension (pO2) in vivo. Use of a double resonant 19F/1H radio frequency coil allows convenient correlation between the high resolution anatomic presentation of proton images and the fluorine distribution. However, quantitative 19F measurements require an RF coil with good H1 field homogeneity over the image volume and a high quality factor (Q) to minimize errors caused by the low signal-to-noise levels available in in vivo imaging and image nonuniformities introduced by the large chemical shift of fluorocarbons.

Cerebral perfusion in children: detection with dynamic contrast-enhanced T2*-weighted MR images.

Cerebral perfusion dynamics were assessed with dynamic contrast material-enhanced T2*-weighted magnetic resonance (MR) imaging in 33 subjects aged 3-20 years. Group A (n = 20) had sickle cell anemia without clinical evidence of cerebrovascular disease. Group B (n = 13) consisted of 12 patients with cerebrovascular disease and homozygous sickle cell anemia and one patient without that anemia.