Improved Conspicuity of Abdominal Lesions with Single-Source Dual-Energy MDCT Hadassah Hebrew University Medical Center Jerusalem, Israel Ruth Eliahou MD, Jacob Sosna, MD AFIIM 2008

1972 – First single slice CT 2005 – Single-Source Dual-Energy MDCT

3 KV Intensity Pre-patient Beam filtration Low-Energy X-ray radiation High-Energy X-ray radiation Spectrum Decomposition Principle: Photons in the x ray beam of the CT scanner have different energies

X-Rays SCINT2 SCINT1 E1 E2  64 detectors  PHILIPS Brilliance CT Prototype  32 detectors for low energy  32 detectors for high energy Dual-Energy CT

low energy image high energy image combined image Each scan creates 3 types of images:

Every pixel has 2 HU values – for high & low energy -986/ / / / / / /147

Dual-Energy CT main advantages:  Separation  Contrast

A separation line can be calculated each material has a different separation line

Materials Separation 1. Iodine 2, Oil 3. 20% oil 5. Calcium 4. Barium 6. Gadolinium 7. Cis Platinum 8. Water 1. Iodine Avg: 319 2, Oil Avg: % oil Avg: Calcium Avg Barium Avg Gadolinium Avg Cis Platinum Avg Water Avg 1.3

Dual-Energy CT main advantages:  Separation  Contrast

CT density of tissues is the result of interactions between x-ray photons and tissues:  Compton scattering  Photoelectric effect Dual-Energy Imaging At Low Voltage: Photoelectric effect is increased Compton scattering is decreased Contrast is improved higher attenuation readings of iodine are obtained

Purpose  To quantitatively and qualitatively evaluate lesion conspicuity & Contrast to Noise ratio of abdominal lesions with DECT.

Materials and Methods  A prospective study (9 / 2006 – 2 / 2008)  Each patient signed an informed consent  All studies were clinically indicated  Study population: 23 patients  Average age 58 years (range 36-86)

Materials and Methods  CT parameters  2-3mm slice thickness  mm increment  140 kVp  mAs  100 cc of nonionic contrast  cc/sec  Regions-of-interest (ROI) were drawn on the lesion evaluated and the adjacent organ

Contrast-to-Noise Ratio  CNR was defined as the difference in attenuation between the lesion and the organ, divided by the air SD for both the low-energy and regular CT images (for fixed ROI)

HU lesion – HU organ SD air CNR =

Lesion Contrast Qualitative Assessment  Low energy and regular CT images were visually compared using the same window  Lesion conspicuity was graded on a predetermined scale  No difference = 0  Significant change = 3

Results  37 lesions  27 solid  10 cystic  Organs  14 kidney  12 liver  5 ovary  4 lymph nodes  2 fluid collections

Results  Improved CNR was noted for both lesion types  Solid lesion CNR  2.11 (SD=0.4) with low energy  1.76 (SD=0.26) for regular CT (p<0.01)  Cystic lesion CNR  8.24 (SD=0.64) with low energy  7.58 (SD=0.46) for regular CT (p<0.03)

Results On visual inspection  Low energy  2.1 for conspicuity & lesion-to-organ contrast, solid lesions  2.4 for cystic lesions  Regular CT  1.8 for conspicuity & lesion-to-organ contrast, solid lesions  2.05 for cystic lesions

Results CombinedLow Energy

Results CombinedLow Energy

So, If better lesion conspicuity Why not scan with low kV all the time ? Noisy image, Data may be lost!

Conclusions  Improved conspicuity of solid and cystic abdominal and pelvic lesions on low energy images obtained using single-source dual-energy MDCT  May enable earlier detection of small lesions and improved diagnosis of neoplastic processes

Work in Progress Digital Subtraction (electronic cleansing) of tagged stool in computed tomographic colonography based on the Dual energy imaging separation capabilities

Our CTC Study:  Aim: To compare prep- less dual energy CTC with OC for evaluation of colorectal polyps  Hypothesis: Dual Energy prep- less CTC can:  reliably detect polyps ≥ 10 mm  Superior digital cleansing

Study design:  100 high risk patients  Will be referred by gastroenterologists to research fellow for preparation guidelines  CTC will be performed and analyzed  3 wks later, OC with video taping will be performed with segmental unblinding as a gold standard