Dual-source spiral CT with pitch up to 3.2 and 75 ms temporal resolution: Image reconstruction and assessment of image quality

• Published in: Medical physics (Lancaster) 2009-12, Vol.36 (12), p.5641-5653
• Main Authors: Flohr, Thomas G., Leng, Shuai, Yu, Lifeng, Allmendinger, Thomas, Bruder, Herbert, Petersilka, Martin, Eusemann, Christian D., Stierstorfer, Karl, Schmidt, Bernhard, McCollough, Cynthia H.
• Format: Article
• Language: English
• Subjects: cardiac CT; Cardiac dynamics; cardiovascular system; CAT SCANNING; Computed radiography; Computed tomography; computerised tomography; CORONARIES; CT image quality evaluation; CT image reconstruction; CYLINDRICAL CONFIGURATION; data acquisition; DATA ACQUISITION SYSTEMS; diagnostic radiography; dosimetry; Dosimetry/exposure assessment; dual source CT; electrocardiography; HEART; IMAGE PROCESSING; image reconstruction; image resolution; Image sensors; Linear Models; Medical image artifacts; Medical image noise; medical image processing; Medical image quality; Medical image reconstruction; Medical imaging; Medical X‐ray imaging; multi-detector row CT; PHANTOMS; Phantoms, Imaging; PMMA; Radiation Dosage; RADIATION DOSES; Radiographic Image Interpretation, Computer-Assisted - methods; RADIOLOGY AND NUCLEAR MEDICINE; Reconstruction; RESOLUTION; Spatial resolution; Time Factors; Tomography, Spiral Computed - methods
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.3259739

Purpose: To present the theory for image reconstruction of a high-pitch, high-temporal-resolution spiral scan mode for dual-source CT (DSCT) and evaluate its image quality and dose. Methods: With the use of two x-ray sources and two data acquisition systems, spiral CT exams having a nominal temporal resolution per image of up to one-quarter of the gantry rotation time can be acquired using pitch values up to 3.2. The scan field of view (SFOV) for this mode, however, is limited to the SFOV of the second detector as a maximum, depending on the pitch. Spatial and low contrast resolution, image uniformity and noise, CT number accuracy and linearity, and radiation dose were assessed using the ACR CT accreditation phantom, a 30 cm diameter cylindrical water phantom or a 32 cm diameter cylindrical PMMA CTDI phantom. Slice sensitivity profiles (SSPs) were measured for different nominal slice thicknesses, and an anthropomorphic phantom was used to assess image artifacts. Results were compared between single-source scans at pitch = 1.0 and dual-source scans at pitch = 3.2 . In addition, image quality and temporal resolution of an ECG-triggered version of the DSCT high-pitch spiral scan mode were evaluated with a moving coronary artery phantom, and radiation dose was assessed in comparison with other existing cardiac scan techniques. Results: No significant differences in quantitative measures of image quality were found between single-source scans at pitch = 1.0 and dual-source scans at pitch = 3.2 for spatial and low contrast resolution, CT number accuracy and linearity, SSPs, image uniformity, and noise. The pitch value ( 1.6 ≤ pitch ≤ 3.2 ) had only a minor impact on radiation dose and image noise when the effective tube current time product (mA s/pitch) was kept constant. However, while not severe, artifacts were found to be more prevalent for the dual-source pitch = 3.2 scan mode when structures varied markedly along the z axis, particularly for head scans. Images of the moving coronary artery phantom acquired with the ECG-triggered high-pitch scan mode were visually free from motion artifacts at heart rates of 60 and 70 bpm. However, image quality started to deteriorate for higher heart rates. At equivalent image quality, the ECG-triggered high-pitch scan mode demonstrated lower radiation dose than other cardiac scan techniques on the same DSCT equipment (25% and 60% dose reduction compared to ECG-triggered sequential step-and-shoot and ECG-gated spiral with x