Review of current applications of spectral CT from head to toe. Contact info: Garry Choy MD MSc, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA

1. Figure 1A -- Myocardial Infraction with DSDECT.
Images acquired by DSDECT demonstrate improved
visualization of delayed enhancement in setting of
myocardial infarction (arrows)
Figure 1B -- Myocardial Profusion with DSDECT.
Filling defects (arrow) in myocardial ischemia are
better visualized with DSDECT
Figures 8A-B -- Differentiation of Hemorrhage from
Contrast with DSDECT.
Virtual non-contrast images which can enable
differentiation of hyperdense hemorrhage (arrow) from
contrast enhancement.
Figures 9A-B -- Beam Hardening Artifact Reduction from
Posterior Fossa.
70keV image (B) shows beam hardening artifacts from posterior fossa (arrow) which can hinder evaluation of brain
stem. In 140keV monochromatic image (B) reduction of artifacts (arrow) is seen.
Figures 12A-B -- Pancreatic Necrosis Assessment with DSDECT.
120kvP weighted image (A) shows a hypoattenuating area (arrow) in the pancreatic tail
region of pig induced by EUS guided microsphere injection representative of necrosis.
Iodine overlay image (B) shows absence of iodine signal within necrotic area (arrow).
Figures 11A-B -- Adrenal Lesion Characterization with DSDECT.
Axial average weighted Dual Energy CT image (A) shows solid left adrenal mass (circle). The density is 42.3 HU. Virtual
non contrast image (B) at same slice position show mass (circle) to be hypoattenuating with density of 1.2 HU which is
consistent with adrenal adenoma. This can essentially eliminate need of unenhanced CT.
Dual source CT is a 64-slice CT with two X-ray
tubes and two detector assembly mounted onto
a gantry with an angle of 90 degrees
Image Based Reconstruction Technology
Both tubes can be operated independently or in
unison with respect to their kV and mA settings.
Tube A has larger FOV of 50cm and Tube B has
relatively smaller FOV of 29cm
Data from the two acquisitions (80 and 140 kVp)
Three Material Decomposition Algorithm
Soft Tissue, Fat, Iodine
Water, Uric Acid,
Calcium
Iodine Distribution and
Virtual Unenhanced
Image
Stone Analysis
The new detector consists of upper and
lower scintillators
– Upper scintillator stops and detects
the lower-energy X-rays
– Bottom scintillator stops and detects
higher-energy X-rays
Signals from both scintillators can
be combined as well
A single X-ray tube is used with
simultaneous acquisition
Single-source ultra-fast kVp switching and near-
perfect helical registration
Projection Based Reconstruction Technology
Full 50cm Scan Field of View
101 user selectable energies
Acquires up to 128 slices per rotation when
using the Gemstone Spectral Imaging
Derives images for the separation of materials
such as calcium, iodine and water
Reduces Beam Hardening artifacts by 50% and
metal artifacts
Data from single acquisitions (80 and 140 kVp)
Post-Processing of Dual Energy Data
140kVp
Image
Monochromatic
Images
Selectable over
Range of 40-140
keV
Material
Density Images
Derived from
Two Material
Decomposition
Effective Z
Image
Garry Choy, MD; Naveen Kulkarni, MD; Brian Ghoshhajra, MD, MBA; Catherine M. Phan, MD; Efren Flores, MD; Anand Singh, MD; Onofrio A. Catalano, MD; Sung Kim, MD; Rajiv Gupta, MD; Dushyant Sahani, MD
Opportunities, Challenges and Applications for Spectral CT Imaging from Head to Toe
MASSACHUSETTS GENERAL HOSPITAL • Department of Radiology • HARVARD MEDICAL SCHOOL
PURPOSE/AIM To review advances in spectral imaging technology with dual-source (DS) and Gemstone Spectral
Imaging (GSI) and the wide spectrum of new CT applications in imaging of various organ systems
from head to toe.
Challenges in Spectral CT Imaging
1. Processed material density images have a different appearance than the standard images
and familiarity with these is needed.
2. By minimizing the number of phases of CT acquisition such as eliminating the unenhanced
and early phase, the effective dose of Dual Engery CT can be substantially lowered. However,
if similar phase acquisition is performed as Singular Energy CT, the radiation dose can be
higher with Dual Engery CT.
3. In Dual-source Dual Engery CT, a smaller field of view with tube B and large body habitus
remains a limitation to exploit benefits for all body parts and patient sizes.
4. Confident characterization of lesions < 5mm in size can be difficult.
5. Image processing and reconstruction of multiple image series from Dual Energy data and
their analysis can also impact the overall CT work flow.
Summary
1. Spectral CT is an exciting technology that empowers CT with new and improved capabilities
for material differentiation, hence a more efficient tissue characterization and lesion
detection method.
2. Spectral CT has the potential to simplify CT acquisition protocols as well as contrast media
utilization while providing desired information and details.
3. Appropriate selection of patients and clinical indications for spectral CT imaging is crucial
to meet the dual objectives of providing high quality care without additional significant
radiation risk.
4. As spectral imaging matures with continued clinical research and becomes
widely available, radiologists will be able to truly harness the power of this
technology in the realm of clinical care.
Figure 10 -- Lung Perfusion Imaging with DSDECT.
DSDECT images of lung perfusion demonstrate perfusion defect consistent
with compromised perfusion in the setting of pulmonary embolism (arrows).
Figures 13A-B -- Differentiating Hemorrhage vs Enhancement in patient
with post RF ablation for HCC with SSDECT.
Contrast enhanced 70keV monochromatic image (A) shows hyperdensity within post
radiofrequency ablation bed (arrow) which could be attributed to hemorrhage secondary to
coagulation necrosis or enhancement. Iodine image (B) does not show enhancement within
ablation bed (arrow) ruling out local recurrence.
Figure 14 -- Stent Patency with SSDECT.
Iodine image confirms stent patency (arrow) even when Dual Energy scan was performed with
low contrast dose of only 30ml.
Figures 15A-B-- Increased Conspicuity of Lesion with Low Energy Monochromatic Image.
40keV monochromatic image (A) shows increased conspicuity of hepatic lesion (arrow) which is
almost indistinct on 70keV image (B).
Figures 2A-B -- Renal Stone Composition with DSDECT.
Color coded images derived from three material decomposition technique showing uric acid stone (arrow)
encoded in red (A) and non uric acid stone (arrow) encoded in blue color (B).
Figures 3A-B -- Renal Mass Characterization
using SSDECT.
120 kvP image (A) shows a complex exophytic
lesion with calcification (arrow) and subtle
hyperdensity in lower pole of right kidney. Iodine
image (B) does not show any enhancement of
lesion (arrow).
Figures 4A-E -- Stone Composition with SSDECT.
On water images (A & C) pure uric acid stones
(arrow) embedded in potatoes and bovine
kidney are seen. Same stones however are
not appreciated on iodine image (B & D). Water and
iodine images thus help in differentiating uric acid
from non uric acid stone. The graph displaying
effective Z vs HU value (E) further helps
differentiating non uric acid stones based on
their effective Z value.
Figures 5A-C -- Renal Lesion Characterization with SSDECT.
Contrast enhanced 70keV image (A) showing exophytic cyst
(arrow) with hyperdensity which is suspicious for malignancy or
could be secondary to hyperdense cyst.
Iodine image (B) and color overlay map (C) shows
that the lesion does not enhance (arrow).
Figures 6A-B -- Evaluation of Hematuria with SSDECT.
Axial monochromatic image in excretory phase (A) shows contrast agent in the left renal collecting system
in 50-year-old evaluated for hematuria. In the same patient water image (B) reconstructed from SSDECT
excretory phase shows a 3mm calculi in calyx (arrow). Water image can essentially eliminate need of
unenhanced CT in detection of urinary tract calculi and can reduced total radiation dose.
Figures 16A-B -- Increased Sensitivity of Endoleak Detection using SSDECT.
On 140kVp image (A) the endoleak (white arrow) and contrast enhancement within stent
(red arrow) are less conspicuous. On 40keV monochromatic image (B) reconstructed from
Dual Energy data endoleak (white arrow) and aortic enhancement (red arrow) is more
conspicuous. Dual Energy CT can thus salvage contrast dose required for CTA but still
achieve optimal contrast enhancement.
Figures 17A-B -- Separation of Calcified Plaque from Contrast with DSDECT.
MIP images of abdominal aorta and iliac arteries before (A) and after (B) subtraction
of calcified plaques enables better quantification of plaque burden and lumen
patency.
Figures 7A-C -- Evaluation of Gout with DSDECT.
Images created with post-processing software specifically for gout based on a three
material decomposition algorithm allowing the characterization of uric acid (colored in
green and arrow) from bone (colored in blue) and bone marrow (colored in pink) for the
2D images. For the 3D image, uric acid is colored in green.
(Image Courtesy of Rajiv Gupta and Catherine Phan)
Figure 18 -- Material Differentiation using Spectral Attenuation
Curve with SSDECT. Spectral attenuation curves of three different
materials are for contrast in abdominal aorta, fat and soft tissue -
corresponding ROI marked in CT. The spectral attenuation curve may
be a signature sign of individual material and may help differentiate
two different materials having similar attenuation values on Single
Energy CT.
Figure 19A-B --
Artifact Reduction
using Metal Artifact
Reduction Algorithm
(MARS) using SSDECT.
70 keV monochromatic
image (A) shows artifacts
caused by coils in left iliac
artery aneurysm obscuring adjacent structure. MARS
image (B) reconstructed from Dual Energy data
shows significant reduction in streak artifacts.
Figure 20A-B -- Artifact Reduction on Iodine Image from SSDECT.
Artifacts caused by surgical clip in 70 keV mono (A) are significantly
reduced in iodine image (B) processed from Dual Energy data.
Figure 21A-B -- Small Lesion Detection on Water Image from
SSDECT. Water image (A) derived from contrast enhanced series
shows two small hepatic lesions (arrows). On routine unenhanced
CT (B) these lesions (arrows) are appreciate as well. Water images can
thus obviate need of unenhanced CT phase in detection of lesion in
solid organs.
Dual Energy CT Principles – Different approaches to Dual Energy ScanningDual Energy CT Principles – Different approaches to Dual Energy Scanning
Dual Source Dual Energy CT - DSDECTDual Source Dual Energy CT - DSDECT
Single Source Dual Energy CT - SSDECTSingle Source Dual Energy CT - SSDECT
Energy Discriminating DetectorsEnergy Discriminating Detectors
WHOLE-BODY WIDE APPLICATIONS
HEART
BRAIN
ADRENALS
BONE
ABDOMEN - KIDNEYS
VASCULAR
ABDOMEN - LIVER
PANCREAS
LUNG
1A 1B2A 2B
3A 3B
4A
4B
4C 4D 4E
Uric Acid Crystals
5A 5B 5C
6A 6B
7A 7B 7C
8A 8B 9A 9B
10
11A 11B
12A 12B
13A 13B 14 15A 15B
16A 16B 17A 17B
18
19A
19B
21A 21B
20A 20B
Uric Acid Stone Non Uric Acid Stone
Subtle Hyperdensity No Enhancement
120 kvP MD Iodine
MD Water Potatoes
Uric Acid Stones Non Uric Acid Stones
MD Iodine Potatoes
Uric Acid Stones Non Uric Acid Stones
MD Water Bovine Kidney
Non Uric Acid Stones Uric Acid Stones
MD Iodine Bovine Kidney
Non Uric Acid Stones Uric Acid Stones
E- Effective-Z vs HU graph to differentiate stones based on Z value
Hyperdensity Cyst No Enhancement No Color Uptake
70keV Mono MD Iodine Color Overlay
70keV Mono MD Water
derived from excretory phase CT
70keV Mono 140keV Mono
Artifacts more
conspicuous
Artifacts less
conspicuous
Average weighted DECT
Artifacts from Coils
Iodine Map120kvP
70keV Mono MD Iodine
Hyperdensity in RFA
site-Hemorrhage/
Enhancement No Enhancement
MD Iodine
Stent Patency
40keV Mono
Increased Lesion Conspicuity Same Lesion is Inconspicuous
140keV
Endoleak Less Conspicuous
70keV Mono
40keV Mono
Endoleak More Conspicuous Before Calcium Subtraction After Calcium Subtraction
70keV Mono
70keV Mono
MARS
70keV Mono MD Iodine
120 kvPMD Water
Reducted Artifacts
Delayed Enhancement
Perfusion Defect
Hemmorrhage Enhancement
Perfusion Defects
Virtual non-contrast
Artifacts from Clips Reducted Artifacts