The nuclear magnetic resonance (NMR) longitudinal relaxation rate R1 dose-response characteristics of a ferrous-sulphate-doped chemical dosimeter system (Fe MRI) immobilized in a gelatin matrix were explored. Samples containing various concentrations of the FeSO4 dosimeter were irradiated to absorbed doses of 0-150 Gy. R1 relaxation rates were determined by imaging the samples at a field strength of 1.5T(1H Lamor frequency of 63.8 MHz). The response of the system was found to be approximately linear up to doses of 50 Gy for all FeSO4 concentrations studied (0.1-2.0 mM). Changing concentrations in the range of 0.1-0.5 mM affected both the slope and intercept of the dose-response curve. For concentrations of 0.5-2.0 mM, the slope of the dose-response curves remained constant at approximately 0.0423 s-1 Gy-1 in the dose range of 0-50 Gy. However, the intercept of the curve continued to increase in that region, as expected, because of the additional paramagnetic ions. The reproducibility of the absorbed dose estimates for measurements made over a 22 cm field of view was found to be 5% in the range of 20-50 Gy (an uncertainty of 0.81 Gy on average), decreasing to approximately 10% in the dose range of 5-10 Gy.

The purpose of this paper is to determine the necessity of a dedicated facial bone/orbital computed tomography (CT) scan for fracture surveillance in patients who have suffered blunt head trauma and whose routine nonenhanced head CT scan is negative. It is based on a retrospective review of 115 patients presenting to the Emergency Department at a level I trauma center after blunt head trauma. Included patients underwent both a nonenhanced head CT scan and a dedicated facial bone or orbit CT. Standard nonenhanced head CT protocol was followed for each patient as per department protocol. A positive head CT scan is defined to include either an air-fluid level within the paranasal sinuses or fracture of the maxillary, orbital, or zygomatic osseous structures. A negative scan demonstrates none of these findings. Intracranial/parenchymal pathology was not evaluated in this study. Sixty-five of the 115 patients had a negative head CT scan as defined above. Of these 65 patients, none subsequently had a positive facial bone or orbit CT scan. The sensitivity and negative predictive values of a negative routine nonenhanced head CT scan for fracture surveillance are both 100%. In the setting of blunt trauma, a negative nonenhanced head CT scan precludes the need for a dedicated facial bone or orbital CT scan in the evaluation for orbital, maxillary, or zygomatic fractures. This saves the patient unnecessary radiation exposure, health care costs, and time spent in the emergency radiology department.

Rod-shaped reflectors such as those used in the AIUM test object resonate at medical ultrasound frequencies, producing artifacts posterior to the reflector. Rods of various diameters and materials were examined to determine their resonant properties, and the effect of the Plexiglas scanning surface of the enclosure on image quality was studied. A theory predicting the resonant frequencies of rods is proposed, and methods of eliminating resonance artifacts are discussed.

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A new test object has been developed that generates images of transducer beam patterns on B-mode hardcopy. The extent and depth of the transducer focal zone are measured from these images. The predictions made from test object images were verified in the clinical images obtained from two 3.5-MHz focused transducers. Using the test object images, we have found that we can make a more rational selection of transducer for each clinical situation.