Biomedical subjects

G C Johnson

Publications and source records attributed to G C Johnson.

94 records · Page 6Linked to original sources

PubMedDate not supplied

A method for describing the doses delivered by transmission x-ray computed tomography.

A method for describing the absorbed dose delivered by x-ray transmission computed tomography (CT) is proposed which provides a means to characterize the dose resulting from CT procedures consisting of a series of adjacent scans. The dose descriptor chosen is the average dose at several locations in the imaged volume of the central scan of the series. It is shown that this average dose, as defined, for locations in the central scan of the series can be obtained from the integral of the dose profile perpendicular to the scan plane at these same locations for a single scan. This method for estimating the average dose from a CT procedure has been evaluated as a function of the number of scans in the multiple scan procedure and location in the dosimetry phantom using single scan dose profiles obtained from five different types of CT systems. For the higher dose regions in the phantoms, the multiple scan dose descriptor derived from the single scan dose profiles overestimates the multiple scan average dose by no more than 10%, provided the procedure consists of at least eight scans.

Biophysical Phenomena↗

PubMedDate not supplied

Periosteal osteosarcoma in the long head of the triceps in a dog.

A 2.5-year-old Labrador retriever was evaluated for forelimb lameness. Fine-needle aspirates of a mass in the proximal brachium were suggestive of a mesenchymal tumor. The dog was euthanized and necropsied. Radiographic evaluation and gross and histopathological findings provided a diagnosis of periosteal osteosarcoma in the long head of the triceps.

Animals↗

PubMedDate not supplied

Assessment and approval of medical devices used in diagnostic imaging in the United States.

Development of new and improved medical imaging technology has been increasing rapidly over the past two decades. While media attention has focused on the revolutionary advances, such as computed tomography, magnetic resonance imaging and metabolic assessment by positron emission tomography, important progress has also been made in the more conventional modalities, including contrast radiography, ultrasound, scintigraphy and mammography. These evolutionary developments have produced fundamental changes in the character of imaging information and in the methods of its acquisition, storage, manipulation, analysis and display. The assessment process-vis-à-vis safety, effectiveness, efficacy or cost-has moved from a previously well-defined physical and engineering evaluation to one of assessing quality, relevance and appropriateness of the "information." A regulatory scheme has evolved in the U.S., whereby the Food and Drug Administration (FDA) is responsible for assuring that new medical devices be approved for commercial distribution only if their safety and effectiveness can be assured. Clear distinctions should be drawn between the FDA "approval" process, assessment of clinical efficacy, and planning for health care delivery.

Certificate of Need↗

PubMedDate not supplied

Gangliosidosis in emus (Dromaius novaehollandiae).

A 6-month-old female emu (Dromaius novaehollandiae) died following acute central nervous system signs. Hematoxylin-and-eosin-stained sections revealed that neurons of the brain were distended with nonstaining 1-to-2-microns vacuoles. Ultrastructural examination of the affected neurons revealed numerous membranous cytoplasmic bodies (MCBs) similar in appearance to the MCBs seen in mammalian gangliosidoses. A full sibling of this emu was donated for study. This 7-month-old female emu was stunted compared with hatchmates. Neurologic examination revealed hypermetric gait, persistent head tremor, and mild ataxia. No gross lesions were evident at postmortem. Histopathologic and electron microscopic findings were similar to those in the index case in that swollen, pale neurons were present in the cerebrum, pons, medulla, cerebellum, spinal cord, spinal ganglia, autonomic ganglia, myenteric plexus, and ganglion cell layer of the retina. Analysis of brain gangliosides of the affected 7-month-old emu revealed 14- and 25-fold increases of GM1 and GM3 gangliosides, respectively, compared with control emus. The total brain ganglioside sialic acids were, on a wet weight basis, 519 micrograms/g (control A), 658 micrograms/g (control B), and 1800 micrograms/g (affected emu). The familial association seen with this condition suggests that emus are affected by an inherited disorder similar to mammalian gangliosidoses.

Animals↗