Contrast-to-noise ratios of liver lesions using subtraction imaging on multiphase 64-detector row CT

• Published in: Clinical radiology 2009-11, Vol.64 (11), p.1075-1080
• Main Authors: Grand, D.J, Beland, M, Dupuy, D, Mayo-Smith, W.W
• Format: Article
• Language: English
• Subjects: Adult; Aged; Aged, 80 and over; Biological and medical sciences; Contrast Media; Female; Humans; Image Enhancement - methods; Investigative techniques, diagnostic techniques (general aspects); Iohexol; Liver - blood supply; Liver - diagnostic imaging; Liver Diseases - diagnostic imaging; Male; Medical sciences; Middle Aged; Radiographic Image Interpretation, Computer-Assisted - methods; Radiology; Retrospective Studies; Tomography, X-Ray Computed - methods
• ISSN: 0009-9260; 1365-229X
• DOI: 10.1016/j.crad.2009.03.013

Aim To measure contrast-to-noise ratios of liver lesions on conventional enhanced and digitally subtracted multidetector row computed tomography (CT) images. Materials/methods This study was approved by our hospital internal review board (IRB) and all collected data were evaluated in a Health Insurance Portability and Accountability Act (HIPAA)-compliant manner. Subtracted datasets, using pixel-by-pixel subtraction of the post-contrast images from the pre-contrast images, were created from the 64 detector-row CT of patients undergoing three-phase examination of the liver (unenhanced, arterial phase, and portal venous phase). Regions of interest were used to calculate the contrast-to-noise ratios between the lesions and the background liver parenchyma on both the post-contrast and subtracted datasets using the following formula: (Lesion mean (HU) – Liver mean (HU))/standard deviation of mean outside patient (HU). These ratios were compared using a mixed linear statistical model. Results Contrast-to-noise ratios were calculated for 64 lesions in 50 consecutive patients. Of the 64 lesions, 42 were hypervascular and 22 were hypovascular. Subtracted datasets yielded statistically significant higher contrast-to-noise ratios of hypervascular lesions compared to normal liver parenchyma ( p < 0.0001). Subtraction did not yield a statistically significant improvement in contrast-to-noise ratios for hypovascular liver lesions ( p = 0.16). Conclusion Post-processed subtraction CT images generate increased contrast-to-noise ratios for hypervascular liver lesions. As this technique is easy to perform and does not involve additional radiation exposure, it should be considered when evaluating for suspected hypervascular lesions.