OBJECTIVE. The purpose of our study was to evaluate the effects of 0.3-second high-resolution CT (HRCT) of the lung using partial reconstruction on cardiac motion artifacts and image noise. SUBJECTS AND METHODS. Thirty-seven pairs of 0.3-second (partial reconstruction) and 0.75-second (full reconstruction) HRCT images were obtained for the lower lung zone during full-inspiration breath-holding. Imaging parameters other than temporal resolution were identical for each patient. Two radiologists visually graded motion artifacts of the cardiac border, bronchi, pulmonary vessels, and fissure in the left lung on a 4-point scale (with 4 indicating no artifacts). The maximum width of motion along the left cardiac border and the area percentage of motion artifacts in the left lung were calculated. Image noise in the air and lung was also determined. Cardiac motion artifacts and image noises were compared between the two sets of CT images. RESULTS. Visual grades for the cardiac border (4±0), bronchi (3.8±0.7), pulmonary vessels (3.6±0.8), and fissure (3.9±0.5) were higher for 0.3-second images than for 0.75-second images (1.7±0.7, 2.0±1.0, 1.6±0.7, and 2.4±0.9, respectively)(p< 0.001). The maximum width of motion along the left cardiac border (0.1±0.5 mm) and the area percentage of motion artifacts in the left lung (6.7%±18.4%) were smaller for 0.3-second images than for 0.75-second images (4.5±1.7 mm and 36.2%±20.9%, respectively)(p< 0.001). Image noises in the air (38.0±9.2) and the lung (86.0±23.1) were greater for 0.3-second images than for 0.75-second images (35.6±9.6 and 76.0±20.3, respectively)(p< 0.01). CONCLUSION. Compared with 0.75-second HRCT using full reconstruction, 0.3-second HRCT using partial reconstruction substantially reduces cardiac motion artifacts in the lung at the expense of increasing image noise. igh-resolution CT (HRCT) of the lung is the accepted diagnostic method for the detection and characterization of various pulmonary parenchymal abnormalities involving the airways, air space, and interstitium [1–4]. HRCT image quality is substantially affected by respiratory motion artifacts, cardiac motion artifacts, and radiation dose. Respiratory motion artifacts can be virtually eliminated if patients hold their breath during the scan, and better breath-holding may be achieved by hyperventilation and administration of oxygen before scanning. Regardless of breath-holding, cardiac motion artifacts can still affect lung images, particularly in the paracardiac regions, and may lead to misinterpretation (eg, bronchiectasis)[2, 5–7]. Cardiac motion artifacts can be reduced by the use of shorter gantry rotation times, prospective ECG triggering, retrospective ECG gating, and partial reconstruction [8–11]. Although associated with an increase in image noise, low-dose

HRCT has been reported to provide diagnosticquality images [12, 13]. Modern CT machines are able to achieve shorter gantry rotation times up to 0.33 seconds, and as a result half-temporal resolution (approximately 0.22 seconds) of the HRCT scan can be obtained using partial reconstruction. The purpose of this prospective study was to evaluate 0.3-second HRCT of the lung using partial reconstruction in terms of cardiac motion artifacts and image noise.