Transcript RSNA 2007

Improved Conspicuity of Abdominal
Lesions with
Single-Source Dual-Energy MDCT
Ruth Eliahou MD, Jacob Sosna, MD
AFIIM 2008
Hadassah Hebrew University Medical Center
Jerusalem, Israel
1972 – First
single slice CT
2005 – Single-Source
Dual-Energy MDCT
Spectrum Decomposition Principle:
Photons in the x ray beam of the CT scanner have
different energies
Intensity
Pre-patient
Beam filtration
Low-Energy
X-ray radiation
High-Energy
X-ray radiation
KV
3
Dual-Energy CT
X-Rays
E1
SCINT1
 64 detectors
 PHILIPS Brilliance CT Prototype
 32 detectors for low energy
E2
 32 detectors for high energy
SCINT2
Each scan creates 3 types of images:
combined image
high energy image
low energy image
Every pixel has 2 HU values – for high & low energy
-106/-135
-986/1003
+23/+35
+119/147
+197/236
+329/389
+191/215
Dual-Energy CT main advantages:
 Separation
 Contrast
A separation line can be calculated
each material has a different separation line
Materials Separation
5. Calcium
5. Calcium
4. Barium
6. Gadolinium
6.
Avg 306
Gadolinium
3. 20% oil7. CisAvg
Platinum
362
7. Cis Platinum
8. Water
1. Iodine
Avg: -16
2, Oil
8. Water
Avg 1.3
Avg 488
3. 20% oil
Avg 26.6
2, Oil
4. Barium
1. Iodine
Avg: 319
Avg: -102
Dual-Energy CT main advantages:
 Separation
 Contrast
Dual-Energy Imaging
CT density of tissues is the result of interactions
between x-ray photons and tissues:
Compton scattering
Photoelectric effect
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
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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)
CNR =
HU lesion – HU organ
SD air
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
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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
Electronic cleansing: dual-energy analysis vs. HU thresholds
Intake of both Iodine and Barium
The colon is partially
filled with stool and
both Iodine contrast
and Barium contrast
Electronic cleansing
with dual-energy
analysis
Electronic cleansing
with high and low
HU thresholds only
1
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