Shmuel Y. Mahgerefteh MD, Presenter: Nothing to Disclose

Michal Haviva Gabbai, Abstract Co-Author: Nothing to Disclose

Jacob Sosna MD, Abstract Co-Author: Consultant, ActiViews Ltd Research grant, Koninklijke Philips Electronics NV

Issac Leichter PhD, Abstract Co-Author: Employee, Siemens AG

New dual-energy CT (DECT) techniques enable simultaneous dual-energy data acquisition. The lower-energy (LE) image should have higher contrast. Our aim was to compare the noise and contrast-to-noise characteristics between high- (HE) and LE images derived from available DECT systems.

A 15-cm phantom was custom-made to hold 10-ml tubes of distilled water and solutions of iodine (I), calcium (Ca) and gadolinium (Ga) at concentrations corresponding to 100-300 HU. Images were acquired at two energy levels using three designated DECT scanners. Dual-source DECT (Siemens) was operated at 140/80 kVp, with or without tin filter, or 140/100 kVp with filter. The mAs values at the HE tube varied from 80 to 309 and at the LE tube from 201 to 440. Rapid kV-switching DECT (GE) was operated at 140/80 kVp with 315 mAs (80/70/60 keV). Dual-layer DECT (Philips) was operated at 140 kVp (88/62 keV) and 120 kVp (82/56 keV) with 400 mAs. The mean HU values and SD values were measured in ROIs fitted to the tubes containing each solution and water, for each dual-energy image. Percent noise was calculated as SD / mean HU value. Contrast-to-noise ratio (CNR) was calculated as the ratio of the difference between mean HU values of solution and water, to SD. Contrast and noise characteristics of the techniques over all settings and scanned materials were evaluated.

For each material and each DECT technique, percent noise was higher in HE than in LE images. At the HE images, the noise values ranged from 2.5% (dual-source DECT, 140 kVp without filter) to 5.1% (dual-layer DECT, 120 kVp). At the LE images, the noise values ranged from 1.2% (rapid kV-switching, 60 keV) to 4.1% (dual-layer, 140 kVp). Conversely, CNR was higher in LE images for each material and each DECT technique. At the HE images, CNR values ranged from 20.0 (dual-layer, 120 kVp) to 40.3 (dual-source, 140 kVp without filter). At the LE images, CNR ranged from 24.5 (dual-layer, 140 kVp) to 86.0 (rapid kV-switching, 60 keV).

LE scanning at all dual-energy techniques yielded characteristically preferable images, with higher CNR and lower noise percentage levels.

As LE images have higher CNR and lower noise percentage levels, these may improve visualization of fine anatomy, e.g. at CTA, and detection of subtle lesions, such as those seen in oncology patients.

Mahgerefteh, S, Gabbai, M, Sosna, J, Leichter, I, Contrast and Noise Characteristics of Available Dual-Energy CT Techniques: Phantom-based Analysis.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11034614.html