Background: Micro-computed tomography offers numerous advantages for small animal imaging, including the ability
to monitor the same animals throughout a longitudinal study. However, concerns are often raised regarding the effects
of x-ray dose accumulated over the course of the experiment. In this study, we scan C57BL/6 mice multiple times per
week for six weeks, to determine the effect of the cumulative dose on pulmonary tissue at the end of the study.
Methods/Results: C57BL/6 male mice were split into two groups (irradiated group=10, control group=10). The
irradiated group was scanned (80kVp/50mA) each week for 6 weeks; the weekly scan session had three scans. This
resulted in a weekly dose of 0.84 Gy, and a total study dose of 5.04 Gy. The control group was scanned on the final
week. Scans from weeks 1 and 6 were reconstructed and analyzed: overall, there was no significant difference in lung
volume or lung density between the control group and the irradiated group. Similarly, there were no significant
differences between the week 1 and week 6 scans in the irradiated group. Histological samples taken from excised lung
tissue also showed no evidence of inflammation or fibrosis in the irradiated group.
Conclusion: This study demonstrates that a 5 Gy x-ray dose accumulated over six weeks during a longitudinal micro-CT
study has no significant effects on the pulmonary tissue of C57BL/6 mice. As a result, the many advantages of micro-
CT imaging, including rapid acquisition of high-resolution, isotropic images in free-breathing mice, can be taken
advantage of in longitudinal studies without concern for negative dose-related effects.
While the Medtronic O-arm was developed for image-guidance applications during orthopedic procedures, it has
potential to assist in cardiac surgical and electrophysiological applications; the purpose of this study was to evaluate the
feasibility of using a mobile conebeam imaging system (O-arm) for gated cardiac imaging. In an in vivo study (two
pigs), projection data from four independently acquired breath-held scans were combined to obtain cardiac gated 3D
images. Projection images were acquired during the infusion of contrast agent and while tracking the ECG. Both
standard and high-definition modes of the O-arm were evaluated. Projection data were retrospectively combined to
generate images corresponding to systole and diastole; different acceptance windows were investigated. The contrast to
noise ratio (CNR) between blood and myocardium was compared for the different gating strategies. Gated cardiac
images were successfully reconstructed with as few as two scans combined (CNR = 2.5) and a window of 200 ms.
Improved image quality was achieved when selecting views based on the minimum time from the selected phase point in
the cardiac cycle, rather than a fixed window; in this case the effective temporal window increased to 475 ms for two
scans. The O-arm has the potential to be used as a mobile cardiac imaging system, capable of three-dimensional
The O-arm (Medtronic Inc.) is a multi-dimensional surgical imaging platform. The purpose of this study was to perform
a quantitative evaluation of the imaging performance of the O-arm in an effort to understand its potential for future nonorthopedic
applications. Performance of the reconstructed 3D images was evaluated, using a custom-built phantom, in
terms of resolution, linearity, uniformity and geometrical accuracy. Both the standard (SD, 13 s) and high definition
(HD, 26 s) modes were evaluated, with the imaging parameters set to image the head (120 kVp, 100 mAs and 150 mAs,
respectively). For quantitative noise characterization, the images were converted to Hounsfield units (HU) off-line.
Measurement of the modulation transfer function revealed a limiting resolution (at 10% level) of 1.0 mm-1 in the axial
dimension. Image noise varied between 15 and 19 HU for the HD and SD modes, respectively. Image intensities varied
linearly over the measured range, up to 1300 HU. Geometric accuracy was maintained in all three dimensions over the
field of view. The present study has evaluated the performance characteristics of the O-arm, and demonstrates feasibility
for use in interventional applications and quantitative imaging tasks outside those currently targeted by the manufacturer.
Further improvements to the reconstruction algorithms may further enhance performance for lower-contrast applications.