Imaging Appearance of Ballistic Wounds Predicts Bullet Composition: Implications for MRI Safety.

OBJECTIVE. The purpose of this article was to determine whether the radiographic and CT appearance of ballistic projectiles predicts their composition and to characterize the translational, rotational, and temperature effects of a 1.5-T MRI magnetic field on representative bullets. MATERIALS AND METHODS. Commercially available handgun and shotgun ammunition representing projectiles commonly encountered in a clinical setting was fired into ballistic gelatin as a surrogate for human tissue, and radiographs and CT images of these gelatin blocks were obtained. MR images of unfired bullets suspended in gelatin blocks were also obtained using T1- and T2-weighted sequences. Magnetic attractive force, rotational torque, and heating effects of unfired bullets were assessed at 1.5 T. RESULTS. Fired bullets were separated into ferromagnetic and nonferromagnetic groups based on the presence of a debris trail and deformation of the primary projectile in the gelatin blocks. Whereas ferromagnetic bullets showed mild torque forces and marked imaging artifacts at 1.5 T, nonferromagnetic bullets did not have these effects. Heating above the Food and Drug Administration limit of 2°C was not observed in any of the projectiles tested. CONCLUSION. Patients with ballistic embedded fragments are frequently denied MRI because the bullet composition cannot be determined without shell casings. We found that radiography and CT can be used to identify nonferromagnetic projectiles that are safe for MRI. We also present an algorithm for determining the triage of patients with retained bullets.

Can the Diagnostic Accuracy of Bone Scintigraphy Be Maintained with Half the Scanning Time?

We aimed to show that the acquisition time of a conventional bone scan could be reduced by half without losing the diagnostic value of the scan. Methods: Fifty adult patients (37 male and 13 female; mean age, 62.5 y; SD, 8.7 y) were enrolled. The patients were injected with 925-1,110 MBq (25-30 mCi) of 99mTc-methylene diphosphonate intravenously. The standard-protocol whole-body planar images were acquired first (scan speed, 10 cm/min; acquisition time, ∼20 min) and were followed immediately by the half-time protocol whole-body planar images (scan speed, 20 cm/min; acquisition time, ∼10 min). Both sets of images were interpreted by 2 nuclear medicine physicians. Each reviewer, when reviewing the standard-protocol images, was self-masked to the result he or she had obtained when reviewing the half-time images, and vice versa. This self-masking was accomplished by allowing a minimum of 2 wk to elapse between the 2 interpretations. We used the κ-coefficient to compare agreement between the standard-protocol results and the half-time results. Results: There was no difference in clinically significant diagnostic information between the half-time and standard protocols. The diagnostic quality of half-time and standard-protocol images did not significantly differ (0.86 < κ < 1.0). Conclusion: Our data suggest that if we reduce the 99mTc-methylene diphosphonate dose by half and keep the acquisition time at its standard value, we gain the benefit of reduced dose without loss of diagnostic value.

Lumbar disc volume measured by MRI: effects of bed rest, horizontal exercise, and vertical loading.

BACKGROUND: Nutrition to the cells in the disc is partly dependent on fluid flowing out during the day and flowing in during bed rest. In spaceflight there are little or no such diurnal changes, since the gravitational load is essentially zero. HYPOTHESIS: The questions we asked were: 1) How much fluid does the disc gain during the night and how quickly does the disc lose fluid during the following day? 2) Is it possible to carry out, in a reasonable amount of time, an exercise regimen on a spacecraft that would be rigorous enough to expel from the disc the equivalent amount of fluid lost during a normal day's activity? METHODS: in five normal subjects, magnetic resonance imaging was used to measure the volume changes (and the corresponding fluid changes) in the lumbar intervertebral discs (L1/L2, L2/L3, L3/L4, L4/L5) before and after a night's bed rest and again at specific intervals during the course of the day while carrying out three different protocols: walking, carrying a backpack, and exercising in a horizontal position. RESULTS: 1) On average the disc gained 10.6% of its volume (or 0.90 cm3 of fluid) during an overnight bed rest; 2) on rising in the morning and after 8 h (using our walking protocol) the disc volume did not decrease to the volume measured at the end of the previous day; and 3) wearing a backpack that weighed 40% of body weight produced a volume decrease equivalent to the decrease in volume obtained at the end of the day, but it took 4 h to do it. CONCLUSIONS: The ability of the disc to retain water is substantial. It would be difficult to carry out an exercise regimen on a spacecraft that would be rigorous enough to expel from the disc the equivalent amount of fluid lost during a "normal" day's activity on Earth.

An in vivo MRI study of the changes in volume (and fluid content) of the lumbar intervertebral disc after overnight bed rest and during an 8-hour walking protocol.

Magnetic resonance imaging (MRI) was used to measure the changes in the volume (and fluid content) of the lumbar intervertebral discs (L1-L2, L2-L3, L3-L4, L4-L5) in five normal subjects. For each subject, MRI scans were taken at the end of a normal day and again on the following morning (after a night's bed rest). Ten further scans were taken during an 8-h protocol consisting of alternate periods of walking (40 min) and scanning (10 min). On average, 1) disc volume increased by 10.6% during overnight bed rest, which corresponds to a gain of about 0.9 cm(3) of fluid; 2) the rate of disc volume decrease during the 8-h walking protocol was 0.96 x 10(-3) cm(3)/min; and 3) after 8 h (using our walking/scanning protocol), the disc volume did not decrease to the volume measured at the end of the previous day.