@article{16666d291f46492596a036429316593d,
title = "A technical solution to avoid partial scan artifacts in cardiac MDCT",
abstract = "Quantitative evaluation of cardiac image data obtained using multidetector row computed tomography (CT) is compromised by partial scan reconstructions, which improve the temporal resolution but significantly increase image-to-image CT number variations for a fixed region of interest compared to full reconstruction images. The feasibility of a new approach to solve this problem is assessed. An anthropomorphic cardiac phantom and an anesthetized pig were scanned on a dual-source CT scanner using both full and partial scan acquisition modes under different conditions. Additional scans were conducted with the electrocardiogram (ECG) signal being in synchrony with the gantry rotation. In the animal study, a simple x-ray detector was used to generate a signal once per gantry rotation. This signal was then used to pace the pig's heart. Phantom studies demonstrated that partial scan artifacts are strongly dependent on the rotational symmetry of angular projections, which is determined by the object shape and composition and its position with respect to the isocenter. The degree of partial scan artifacts also depends on the location of the region of interest with respect to highly attenuating materials (bones, iodine, etc.) within the object. Single-source partial scan images (165 ms temporal resolution) were significantly less affected by partial scan artifacts compared to dual-source partial scan images (82 ms temporal resolution). When the ECG signal was in synchrony with the gantry rotation, the same cardiac phase always corresponded to the same positions of the x-ray tube(s) and, hence, the same scattering and beam hardening geometry. As a result, the range of image-to-image CT number variations for partial scan reconstruction images acquired in synchronized mode was decreased to that achieved using full reconstruction image data. The success of the new approach, which synchronizes the ECG signal with the position of the x-ray tube(s), was demonstrated both in the phantom and animal experiments.",
keywords = "CT artifacts, CT perfusion, Cardiac CT, Multidetector row CT, Partial scan reconstruction",
author = "Primak, {A. N.} and Y. Dong and Dzyubak, {O. P.} and Jorgensen, {S. M.} and McCollough, {C. H.} and Ritman, {E. L.}",
note = "Funding Information: Erik Ritman, Steven Jorgensen, and Yue Dong were supported by NIH Grant No. HL72255. The authors would like to thank Patricia Beighley for assistance with the animal preparation and subsequent CT scanning procedures, and Kris Nunez for assistance with manuscript submission. FIG. 1. A phantom used for daily water calibrations of the scanner. The water-filled, 20 cm diameter section of this phantom was used. The cantilevered design ensures no table attenuation is present in the scan plane. FIG. 2. An anthropomorphic cardiac phantom (QRM, M{\"o}hrendorf, Germany) with its central portion replaced with a water-filled tank. The syringe centered in the middle of the tank was filled with water and iodine solutions. FIG. 3. Signals recorded during synchronous operation of the scanner with cardiac pacing at 90.9 bpm. Time scale is 60 ms/division. The rising edge of the x-ray detector signal (top trace) triggers the Exact Output signal, generating the 600 ms pulse which “covers up” the second set of x-ray pulses. The rising edge of the Exact Output signal triggers the S8800 Pacer & ECGTrig. The resulting pacing of the pig{\textquoteright}s heart is shown in the ECG line. The bottom trace is the signal sent to the scanner{\textquoteright}s ECG input. FIG. 4. Photograph of the x-ray tube position detector installed on the scanner. The infrared source and detector are mounted on Plexiglas “fingers” that swivel to provide alignment of the source and detector so that reflection from the counterweight is reliably detected, but reflections off of the gantry surface are ignored. FIG. 5. (a) The water phantom aligned exactly at the isocenter without table attenuation. (b) In this perfectly symmetric setting, both full and partial scan reconstruction images have the same range of the CT number variations. (c) The water phantom located 10 cm off the isocenter. (d) Moving the phantom off the isocenter creates enough anisotropy to cause partial scan artifacts. The partial scan has a 7.6 times larger range of CT number variations compared to the full scan. FIG. 6. (a) The cardiac phantom with the water-filled syringe aligned at scanner isocenter. (b) The phantom geometry has enough anisotropy to cause mild to moderate partial scan artifacts, depending on the ROI location. (c) The cardiac phantom with the iodine-filled (2000 HU) syringe located 10 cm off the isocenter. (d) This geometry has large anisotropy, resulting in moderate to severe partial scan artifacts, depending on the ROI location. FIG. 7. The maximum range of the image-to-image variations in a mean CT number for any evaluated ROI for full and partial scans of the cardiac phantom located at isocenter and 10 cm off the isocenter, as a function of the iodine attenuation inside the phantom. FIG. 8. The maximum range of the image-to-image variations in a mean CT number for any evaluated ROI for synchronized and nonsynchronized partial scans of the cardiac phantom, as a function of the heart rate. The phantom was centered at the isocenter. The synchronized scans were performed for heart rate of 60.6 and 90.9 bpm. FIG. 9. (a) Maximum intensity projection (MIP) image from the animal study in the absence of iodine contrast. (b) Noncontrast data show a drastic reduction in the CT number variations for the synchronized mode (square). (c) MIP image with the contrast enhancement of the myocardium (d) Myocardial perfusion data for the nonsynchronized mode (triangle) are degraded by partial scan artifacts. FIG. 10. Diagram showing the principle of the partial scan artifact and how it can be eliminated by synchronizing the heart rate with the gantry rotation rate. The nonsynchronized sequence is shown for the HR of 70 bpm, while the synchronized sequence corresponds to the HR of 60.6 bpm. The gantry rotation period is 330 ms. ",
year = "2007",
doi = "10.1118/1.2805476",
language = "English (US)",
volume = "34",
pages = "4726--4737",
journal = "Medical physics",
issn = "0094-2405",
publisher = "AAPM - American Association of Physicists in Medicine",
number = "12",
}