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Biomedical subjects

A L Hopkins

Publications and source records attributed to A L Hopkins.

26 records · Page 2Linked to original sources
PubMed1988

Improved sensitivity of proton MR to oxygen-17 as a contrast agent using fast imaging: detection in brain.

The potential utility of H2(17)O as a contrast agent has been demonstrated in biological solutions and isolated tissues but its use has been impaired by the need to run heavily T2-weighted spin-echo images. By choosing an appropriate steady-state free precession experiment sensitive to T1/T2, we have improved the available contrast-to-noise per unit time by more than a factor of 5. This allows easy measurement of the proton effects for concentrations as low as 0.4% H2(17)O in less than 1 min. Injection into small animals produces a marked reduction in the overall image intensity. Consecutive imaging at the rate of one every 52 s has been used to follow the rate of change in brain image intensity immediately after injection.

Animals↗
PubMed1988

Oxygen-17 contrast agents. Fast imaging techniques.

Under physiologic conditions the stable isotope oxygen-17, in the form of O-17 water, lowers the proton T2 of blood, CSF, tissues, and whole organisms. With MRI the resulting changes in intensity can be detected using spin-echo pulse sequences, but much greater sensitivity is achieved in a fraction of the time with a steady-state free precession sequence such as FISP. With this sequence it is possible to detect levels as low as 0.4% Oxygen-17 water in 53 seconds or less.

Contrast Media↗
PubMed1987

Oxygen-17 compounds as potential NMR T2 contrast agents: enrichment effects of H2(17)O on protein solutions and living tissues.

The isotopic enrichment of solutions, living tissues, and organisms with oxygen-17 in the form of H2(17)O shortens their proton NMR transverse relaxation times (T2) and produces changes in NMR image intensity. The transverse relaxation rate (1/T2) was found to be linearly dependent on the H2(17)O concentration in biological solutions up to 5% enrichment. The longitudinal relaxation time (T1) is not affected by enrichment. Equal concentrations of H2(17)O do not produce the same magnitude of T2 change in all physiological environments. The reasons for these differences are discussed. The results suggest that certain oxygen-17 compounds should be explored as "contrast agents" in magnetic resonance imaging.

Animals↗
PubMed1986

Multiple field strength in vivo T1 and T2 for cerebrospinal fluid protons.

To estimate the feasibility of measuring in vivo CSF protein, oxygen, or other solutes through their effect on proton relaxation times, the T1 and T2 of CSF protons has been measured within the human lateral ventricles. T1 was measured at 6.25, 25.4, and 60.1 MHz with a two-point method. T2 was measured at 6.25 and 25.4 MHz using the CPMG sequence to acquire 8 echo images. The T1 was 4.3 s with no evidence of field dependence. The T2 was 2 s. Although these values approach those for water at the same temperature it is possible that the T1 is influenced by the normal oxygen concentration. Calculations based on the relaxivity of dissolved protein indicate that the use of these methods for the detection of elevated levels of CSF protein would be less sensitive than existing methods.

Cerebral Ventricles↗
PubMedDate not supplied

Subdural hematoma in a dog.

A traumatic subacute subdural hematoma in a dog was diagnosed by computed tomography and treated successfully by craniectomy and surgical drainage.

Acute Disease↗
PubMedDate not supplied

Acute, flaccid quadriplegia in three cats with suspected coral snake envenomation.

Three cats were evaluated for acute, ascending, flaccid quadriplegia; depression; and reduced nociception. Complete or partial neuromuscular junction blockade was found on nerve stimulation studies during electromyographic examinations. Two of the cases had wounds on the chin or paw compatible with coral snake bites. Although a coral snake was found in only one case, coral snake envenomation was suspected because potential for exposure, clinical signs, and electrodiagnostic findings were similar to dogs reported with this condition and to cats with tiger snake envenomation. Only one case received coral snake antivenin. All cases recovered within seven-to-10 days.

Acute Disease↗