title: Coronary CT angiography in step-and-shoot technique with 256-slice CT: impact of the field of view on image quality, craniocaudal coverage, and radiation exposure.
abstract: OBJECTIVE
  To evaluate the effect of a small field of view (FOV) for step-and-shoot coronary computed tomography angiography (CCTA) on craniocaudal z-coverage per scan step, image quality, and radiation exposure.
  
  
  METHODS
  53 patients underwent prospectively ECG-gated CCTA on a 256-slice MDCT scanner using either a FOV > 250 mm (group 1, n = 29) or a FOV ≤ 250 mm (group 2, n = 24). Craniocaudal z-coverage was determined on coronal multiplanar reformations. Image noise, signal-to-noise ratio, contrast-to-noise ratio, and qualitative image parameters were assessed. Radiation dose was estimated from the dose length product and was standardized for a scan range from the main pulmonary artery to the diaphragm in order to make both groups comparable.
  
  
  RESULTS
  Diagnostic image quality was achieved in 91.3% of the coronary artery segments of group 1 and 89.9% in group 2 (p = 0.201). There were no major differences in image noise, SNR, and CNR between both groups. A smaller FOV leads to an increase of craniocaudal coverage of a single CT scan step (r = -0.879; p ≤ 0.001). There was an increase of 23.8% of the mean z-coverage per scanned subvolume in group 2 (59.9 mm vs. 48.8mm). Radiation dose was significantly lower in group 2 (229 vs. 285 mGy cm, respectively).
  
  
  CONCLUSIONS
  The use of a small transverse FOV for step-and-shoot CCTA at a wide detector CT scanner leads to an increased z-coverage. 2 scan volumes are enough to image the cardiac anatomy. Radiation dose is decreased without negative impact on image quality.
authors.affiliation: Klinikum rechts der Isar der, Technischen Universität München, Department of Radiology, Ismaninger Str 22, 81675 München, Germany. muenzel@tum.de
authors.forename: Daniela
authors.initials: D
authors.lastname: Muenzel
authors.forename: Peter B
authors.initials: PB
authors.lastname: Noel
authors.forename: Franziska
authors.initials: F
authors.lastname: Dorn
authors.forename: Martin
authors.initials: M
authors.lastname: Dobritz
authors.forename: Ernst J
authors.initials: EJ
authors.lastname: Rummeny
authors.forename: Armin
authors.initials: A
authors.lastname: Huber
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D055424:Cardiac-Gated Imaging Techniques; D016009:Chi-Square Distribution; D003287:Contrast Media; D017023:Coronary Angiography / Q000379:methods*; D003324:Coronary Artery Disease / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D007479:Iopamidol / Q000031:analogs & derivatives; D008297:Male; D008875:Middle Aged; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D012189:Retrospective Studies; D012307:Risk Factors; D018709:Statistics, Nonparametric; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D003287:Contrast Media; C057937:iomeprol; D007479:Iopamidol