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Objective: To test a low dose, low voltage protocol for the diagnosis of pulmonary embolism., Materials and Methods: 50 Patients with clinically suspected pulmonary embolism underwent CTPA with 80kVp and 295mAs (test group) on a 64-row MDCT scanner. These patients were compared to a similar group of 50 patients scanned on the same scanner with the 120kVp protocol with automatic tube current modulation (control group). All patients received 100-110ml of a 370mgI/ml solution at 4.5cm(3)/s. Scans were compared for quantitative imaging parameters (attenuation and standard deviation in the main, right and left pulmonary arteries, in a lobar and segmental pulmonary artery and in the aorta) and for dose parameters (CTDI and DLP), using an unpaired t-test. Phantom measurements were also performed for image quality parameters and radiation dose., Results: Mean attenuation was significantly higher in the test group than in the control group in the main pulmonary trunk, in the right pulmonary artery, in the left pulmonary artery, in a lobar and segmental pulmonary artery and in the ascending aorta (all: p≤0.0001). Noise was significantly higher in the test group than in the control group, but contrast to noise ratio was not significantly different between the two protocols. Radiation dose was significantly lower in the test group than in the control group, as measured by CTDI, DLP and effective dose to organs (all: p<0.0001)., Conclusions: The use of 80kVp for pulmonary CTA significantly reduces patient radiation exposure, and significantly increases contrast medium attenuation in the pulmonary arteries, with no effect on the diagnostic quality of the exams., (Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.)

Preprocessing, binning and dataset subsampling are investigated with regard to simultaneous maximisation of the speed, accuracy and robustness of CT-3D rotational angiography (3DRA) registration. Clinical diagnosis and treatment can both take advantage of this integration, because 3DRA allows the shape of vessel structures to be evaluated three-dimensionally with respect to standard 2D projective angiography. The method for optimising preprocessing, binning and subsampling consisted of independent variation of the corresponding parameters to maximise robustness and speed while maintaining subvoxel accuracy; the latter was computed as the sum of the mean squared errors initially present in the registrations with the errors relative to both binning and subsampling. The results suggest the choice of 256 bins, steps between 14 mm (coarse optimisation) and 2.5 mm (fine optimisation) and bone segmentation by threshold, for binning, subsampling and preprocessing, respectively. The application of this parameter set-up to 50 CT-3DRA registrations resulted in a saving, on average, of 40% of the time with respect to the method previously used, while registration error was maintained within 2 mm (1.97 mm, 90% confidence interval) and robustness was increased, so that no manual initial realignment was needed in 48 registrations. Validation by the registration of images acquired for a head phantom showed subvoxel residual errors. In conclusion, the proposed procedure can be considered a satisfactory strategy to optimise CT-3DRA registration.

In this paper a novel technique is proposed and validated for radiosurgery treatment planning of arteriovenous malformations (AVMs). The technique was developed for frameless radiosurgery by means of the CyberKnife, a nonisocentric, linac-based system which allows highly conformed isodose surfaces to be obtained, while also being valid for other treatment strategies. The technique is based on registration between computed tomography (CT) and three-dimensional rotational angiography (3DRA). Tests were initially performed on the effectiveness of the correction method for distortion offered by the angiographic system. These results determined the registration technique that was ultimately chosen. For CT-3DRA registration, a twelve-parameter affine transformation was selected, based on a mutual information maximization algorithm. The robustness of the algorithm was tested by attempting to register data sets increasingly distant from each other, both in translation and rotation. Registration accuracy was estimated by means of the "full circle consistency test." A registration quality index (expressed in millimeters) based on these results was also defined. A hybrid subtraction between CT and 3DRA is proposed in order to improve 3D reconstruction. Preprocessing improved the ability of the algorithm to find an acceptable solution to the registration process. The robustness tests showed that data sets must be manually prealigned within approximately 15 mm and 20 degrees with respect to all three directions simultaneously. Results of the consistency test showed agreement between the quality index and registration accuracy stated by visual inspection in 20 good and 10 artificially worsened registration processes. The quality index showed values smaller than the maximum voxel size (mean 0.8 mm compared to 2 mm) for all successful registrations, while it resulted in much greater values (mean 20 mm) for unsuccessful registrations. Once registered, the two data sets can be used for CyberKnife treatment planning. Target delineation is performed on 3DRA while dose calculation and DRR generation are performed on CT. In conclusion, a method was developed for using 3DRA images for AVM frameless radiosurgery treatment planning. The method proved to be feasible, robust, and accurate for clinical use. 3DRA can be performed at different times or locations compared to standard, frame based stereotactic angiography. Unlike two-dimensional angiography, 3DRA allows examination of the shape of the AVM and of the surrounding target from any arbitrary point of view during treatment planning. The method can be applied to any case of intermodality registration, is operator-independent, and allows estimation of registration quality. Further research is desirable to improve time resolution in order to distinguish between feeding and draining vessels.