In order to decrease the patient's radiation exposure from Computed Tomography, the new CT geometry CTDOR has
been invented. It consists of two data sets: A conventional arc or flat panel detector and a mask ring with shieldings on
the outside and detectors on the inside separated by windows. Combined with the reconstruction algorithm OPED, it has
the theoretical potential to decrease the dose about 50% while providing the same image quality as conventional systems.
First steps to evaluate this theory were done with a mask ring demonstrator combined with a conventional C-arm device.
Although the quality of the demonstrator is limited, this set-up was supposed to demonstrate how the combination of the
two data sets works in principle. Preliminary results from earlier studies, however, provided images of rather poor quality.
This work presents better images obtained with an optimized data treatment. We showed that most artifacts are eliminated
and that we get sharper images with higher contrast compared to the images reconstructed from the single data sets and
compared to the earlier study. Regarding the limitations of the set-up, the resulting images were remarkably good. CTDOR
is therefore a promising method, which is worth to perform further studies.
The sampling geometry of CT-scanners plays an important role in the reconstruction of images. We have
previously reported a test-device that directly collects the Radon data within a special scanning geometry, whose
acquired data can be efficiently treated with series expansion algorithms such as, for example, OPED (Orthogonal
Polynomial Expansion on Disc). This geometry has the potential of reducing the radiation exposure of the patient
by about a factor of two. However, a fourth of the data must be obtained by interpolation within the measured
projections. In this contribution, we show by a Monte Carlo simulation that this interpolation has no significant
influence on the quality of the reconstructions.
Preliminary results for a new CT scanning device with dose-reduction potential were presented at the SPIE
Medical Imaging conference 2007. The new device acquires the Radon data after the X-ray beam is collimated
through a special mask. This mask is combined with a new and efficient data collection geometry; thus the device
has the potential of reducing the dose by a factor of two. In this work, we report the first complete proof of the
idea using the same simplified mask of 197 detectors as last year, and a clinical C-arm with a flat panel detector
to simulate the gantry. This addition enables the acquisition of two independent and complementary data sets
for reconstruction. Moreover, this clinical set-up enables the acquisition of data for clinically relevant phantoms.
Phantom data were acquired using both detector sets and were reconstructed with the robust algorithm OPED.
The independent sinograms were matched to a single one, and from this a diagnostic image was reconstructed
successfully. This image has improved resolution, as well as less noise and artifacts compared to each single
independent reconstruction. The results obtained are highly promising, even though the current device acquires
only 197 views. Dose comparisons can be carried out in the future with a more precise prototype, comparable
to current clinical devices with respect to imaging performance.
A non-standard scanning device with dose-reduction potential was proposed at the SPIE Medical Imaging conference
2006. The new device obtains the Radon data after the X-ray beam is collimated through a special
mask. This mask is combined with a new geometry that permits an efficient data collection, thus the device
has the potential of reducing the dose by a factor of two. In this work, we report a prototype of the new device
and experimental data acquisition using only the mask of the new scanning geometry. In order to obtain the
optimal parameters for the scanning device, several factors have been considered, including detector elements
and shielding shape, fan beam angle, speed of the source rotation and materials employed. The calibration of the
detector elements needs especial attention, due to the dependence of the detector response on the energy of the
X-rays. A simplfied version of the device was designed and mounted. Phantom data were acquired using this
prototype and were used to test the performance of the new design. The results obtained are highly promising,
even though the prototype developed does not make use yet of all the potential features proposed in the theory.