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. 2008 Oct;35(10):4757-64.
doi: 10.1118/1.2989989.

Rotational micro-CT using a clinical C-arm angiography gantry

V Patel, K R Hoffmann, C N Ionita, C Keleshis, D R Bednarek, S Rudin

Rotational micro-CT using a clinical C-arm angiography gantry

V Patel et al. Med Phys. 2008 Oct.

Abstract

Rotational angiography (RA) gantries are used routinely to acquire sequences of projection images of patients from which 3D renderings of vascular structures are generated using Feldkamp cone-beam reconstruction algorithms. However, these systems have limited resolution (<4 lp/mm). Micro-computed tomography (micro-CT) systems have better resolution (>10 lp/mm) but to date have relied either on rotating object imaging or small bore geometry for small animal imaging, and thus are not used for clinical imaging. The authors report here the development and use of a 3D rotational micro-angiography (RMA) system created by mounting a micro-angiographic fluoroscope (MAF) [35 microm pixel, resolution >10 microp/mm, field of view (FOV)=3.6 cm] on a standard clinical FPD-based RA gantry (Infinix, Model RTP12303J-G9E, Toshiba Medical Systems Corp., Tustin, CA). RA image sequences are obtained using the MAF and reconstructed. To eliminate artifacts due to image truncation, lower-dose (compared to MAF acquisition) full-FOV (FFOV) FPD RA sequences (194 microm pixel, FOV=20 cm) were also obtained to complete the missing data. The RA gantry was calibrated using a helical bead phantom. To ensure high-quality high-resolution reconstruction, the high-resolution images from the MAF were aligned spatially with the lower-dose FPD images, and the pixel values in the FPD image data were scaled to match those of the MAF. Images of a rabbit with a coronary stent placed in an artery in the Circle of Willis were obtained and reconstructed. The MAF images appear well aligned with the FPD images (average correlation coefficient before and after alignment: 0.65 and 0.97, respectively) Greater details without any visible truncation artifacts are seen in 3D RMA (MAF-FPD) images than in those of the FPD alone. The FWHM of line profiles of stent struts (100 microm diameter) are approximately 192+/-21 and 313+/-38 microm for the 3D RMA and FPD data, respectively. In addition, for the dual-acquisition 3D RMA, FFOV FPD data need not be of the highest quality, and thus may be acquired at lower dose compared to a standard FPD acquisition. These results indicate that this system could provide the basis for high resolution images of regions of interest in patients with a reduction in the integral dose compared to the standard FPD approach.

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Figures

Figure 1
Figure 1
(Left) Picture of the MAF. (right) Schematic diagram of the MAF.
Figure 2
Figure 2
MAF attached to a commercial C-arm gantry using a custom-made support arm.
Figure 3
Figure 3
(left) MAF swung out of the FOV to acquire data using the FPD. (right) MAF swung in the FOV to acquire data using the MAF.
Figure 4
Figure 4
Image of a rabbit with coronary stent acquired by (left) FPD and (right) MAF. The dotted circle in the left image shows the FOV of the MAF within the FOV of the FPD.
Figure 5
Figure 5
MAF data placed inside the ROI in the FPD image (left) before and (right) after spatial registration. The registration process allows the FPD geometric calibrations needed for the reconstruction to be used for the MAF acquisitions. In addition, it removes discontinuities at the edge of the ROI and enables one-to-one pixel correspondence between the FPD and MAF data to determine the pixel value mapping.
Figure 6
Figure 6
Illustration of the effect of intensity correction. (Top row) (left) The FPD data do not match well with the replaced MAF data. (right) A reconstructed axial slice shows artifacts at the edge of the ROI due to intensity mismatch. (Bottom row) (left) After intensity correction, the FPD data are well matched with the MAF data, and (right) the artifacts are eliminated in the reconstructed slice.
Figure 7
Figure 7
Illustration of resolution quality. (Top row) Axial slices of a volume reconstructed with 25 μm voxels using (left) only FPD data and (right) the 3D RMA technique. (Bottom row) Corresponding line profiles across the two stent struts indicated by the arrow.
Figure 8
Figure 8
FWHMs of a single strut of the stent measured in incrementing axial slices reconstructed using the FPD data only and using the 3D RMA technique.
Figure 9
Figure 9
Volume rendering of the stent and bone tip, reconstructed using the new 3D RMA technique.
See this image and copyright information in PMC

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