here are the few technical diffferences between computed tomography and cone beam ct scans.
DIFFERENCE BETWEEN COMPUTED TOMOGRAPHY AND CONE BEAM CT SCAN
In helical CT, the patient is advanced through the scanner with the x-ray source and detector continuously rotating about the gantry. CBCT acquires information using a high-resolution two-dimensional detector instead of multiple one-dimensional (1D) detector elements.
In multi-detector spiral CT, the patient is
scanned in a helical fashion with gantry speeds on the order Of 0.4 seconds for
current state-of-the-art 64-slice scanners. With a detector row width of
0.5–0.6 mm, coverage of approximately 4 cm in the z-axis allows large
anatomical regions to be imaged in several seconds. CBCT systems, current
detector arrays are 40 x 30 cm2, allowing 25 x 25 x 18 cm3 volumetric datasets
to be generated in a single rotation of the source and detector.
CBCT systems currently available require
5–20 seconds for image acquisition.
The multidetector CT Image acquisition is
actually more rapid. The mathematical complexity of the cone-beam
reconstruction algorithm, which is a modification of the algorithm initially
described by Feldkamp, state-of-the-art C-arm CBCT systems require 1 minute of
post-processing time for image reconstruction, compared to substantially
real-time image reconstruction for multidetector CT.
CBCT spatial resolutions similar to, if not
slightly more substantial than, those of multidetector CT. With 2048 x
1538 detector elements, isotropic voxel sizes of under 200 x 200 x 200 µm3 are
achievable with current C-arm CBCT systems. Isotropic voxel size of 600 x 600 x
600 µm3 can be obtained from current state-of-the-art 64- slice scanners. This
ct resolution can also be achieved ib cbct, but, patient dose considerations
make utilisation of this high resolution impractical (and unnecessary) for most
imaging applications.
In cbct, it’s not the Pixel size that
actually determines the resolution. The spatial resolution and noise for the
flat-panel detector-based system is governed primarily by blur in the x-ray
converter (CsI: Tl) (and reconstruction filter), rather than pixel size,
limiting the practical voxel size of current C-arm CBCT systems.
The most significant difference between 3D
tomographic datasets generated via a cone-beam geometry versus a fan-beam
geometry is the considerable increase in scattered radiation with CBCT. multi-detector
CT scanners employ anti-scatter septae between the individual detector
channels. Anti-scatter septae of this nature cannot be used with flat-panel
detectors. The critical point is that increased scatter radiation due to
wider x-ray beam collimation in CBCT leads to significant degradation of image
quality.
To account for the increased scatter,
multiple anti-scatter techniques have been investigated for use with CBCT
systems including, anti-scatter grids, software correction algorithms,
beam-stop scatter mapping and adjustment of object-to-detector distance
(air-gap).
The limitation of 15 frames-per-second
(fps) at full resolution is due to the intrinsic properties of the CsI
scintillator, which suffers from more significant lag (afterglow) compared to
multidetector CT ceramic detectors.
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