Improved Conspicuity of Abdominal Improved Conspicuity of Abdominal Lesions with Lesions with

Single-Source Dual-Energy MDCTSingle-Source Dual-Energy MDCT

Hadassah Hebrew University Medical CenterJerusalem, Israel

Ruth Eliahou MD, Jacob Sosna, MD

AFIIM 2008

1972 – First single slice CT 20052005 – – Single-SourceSingle-Source

Dual-Energy MDCTDual-Energy MDCT

3

KV

Intensity

Pre-patient Beam filtration

Low-Energy X-ray radiation

High-Energy X-ray radiation

Spectrum Decomposition Principle: Spectrum Decomposition Principle: Photons in the x ray beam of the CT scanner have

different energies

X-Rays

SCINT2

SCINT1E1

E2

64 detectors

PHILIPS Brilliance CT Prototype

32 detectors for low energy

32 detectors for high energy

Dual-Energy CTDual-Energy CT

low energy imagelow energy image

high energy imagehigh energy image

combined imagecombined image

Each scan creates 3 types of images:Each scan creates 3 types of images:

Every pixel has 2 HU values – for high & low energyEvery pixel has 2 HU values – for high & low energy

-986/1003-986/1003

+23/+35+23/+35

+197/236+197/236

-106/-135-106/-135

+191/215+191/215+329/389+329/389

+119/147+119/147

Dual-Energy CT main advantages:

Separation

Contrast

A separation line can be calculated

each material has a different separation lineeach material has a different separation line

Materials Separation

1. Iodine

2, Oil

3. 20% oil

5. Calcium4. Barium

6. Gadolinium

7. Cis Platinum

8. Water1. IodineAvg: 319

2, OilAvg: -102

3. 20% oilAvg: -16

5. CalciumAvg 306 4. Barium

Avg 4886. Gadoliniu

m Avg 3627. Cis Platinum

Avg 26.6

8. WaterAvg 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: At Low Voltage:

Photoelectric effectPhotoelectric effect is increased is increased

Compton scatteringCompton scattering is decreased is decreased

ContrastContrast is improved is improved

higher attenuation readings of iodine are obtainedhigher 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 1-1.5 mm increment 140 kVp 250-300 mAs 100 cc of nonionic contrast 1.5-2 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 airCNR =

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

Combined Low Energy

Results

Combined Low 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

1

Electronic cleansingwith dual-energy analysis

Electronic cleansingwith high and low HU thresholds only

The colon is partially filled with stool and both Iodine contrastand Barium contrast

Electronic cleansing: dual-energy analysis vs. HU thresholdsIntake of both Iodine and Barium

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