Relative new approach

1. DUAL-ENERGY CT
EVALUATION OF
GASTROINTESTINAL
BLEEDING
ORIGINAL ARTICLE
DANE ET
RSNA RADIOGRAPHICS MAY 23

3. • Gastrointestinal (GI) bleeding is a potentially life-
threatening condition.
• Multidetector abdominopelvic CT angiography is
commonly used in the evaluation of patients with GI
bleeding.
• Given that many patients with severe overt GI bleeding
are unlikely to tolerate bowel preparation, and
inpatient colonoscopy is frequently limited by
suboptimal preparation obscuring mucosal visibility,
CT angiography is recommended as a first-line
diagnostic test in patients with severe hematochezia to
localize a source of bleeding.

4. • Assessment of these patients with conventional single-
energy CT systems typically requires the performance of a
noncontrast series followed by imaging during multiple
postcontrast phases. Dual-energy CT (DECT) offers
several potential advantages for performing these
examinations.
• DECT may eliminate the need for a non-contrast
acquisition by allowing the creation of virtual non-contrast
(VNC) images from contrast-enhanced data, affording
significant radiation dose reduction while maintaining
diagnostic accuracy.
• VNC images can help radiologists to differentiate active
bleeding, hyper- attenuating enteric contents, hematomas,
and enhancing masses.

5. • Additional postprocessing techniques such as low–kiloelectron
voltage virtual monoenergetic images, iodine maps, and iodine
overlay images can increase the conspicuity of contrast
material extravasation and improve the visibility of subtle
causes of GI bleeding, thereby increasing diagnostic
confidence and assisting with problem solving.
• GI bleeding can also be diagnosed with routine single-phase
DECT scans by constructing VNC images and iodine maps.
• GI bleeding can also be diagnosed with routine single-phase
DECT scans by constructing VNC images and iodine maps.

6. BASIC PRINCIPLE
• Conventional single-energy CT scanners use a polychromatic photon
beam with a single peak voltage and single detector array. These
systems calculate the attenuation of tissue in Hounsfield units in each
voxel.
• DECT systems allow acquisition of two different data sets using high-
and low-energy spectra DECT systems allow differentiation between
materials when their attenuation properties vary at the two energy
levels.
• If an iodine-containing voxel and a noniodine soft-tissue–containing
voxel measure the same attenuation when assessed at the high-energy
spectra, then the iodine-containing voxel will appear more
hyperattenuating at the low-energy spectra.
• This variation in attenuation at the two energy levels allows DECT to
be used for detection and quantification of the presence of iodine.

7. FIGURE 1. ILLUSTRATIONS SHOW DUAL-ENERGY CT SYSTEMS. (A) RAPID KILOVOLTAGE-SWITCHING CT SYSTEM.
WITH THIS SYSTEM, THE TUBE VOLTAGE IS RAPIDLY ALTERNATED FROM LOW TO HIGH VOLTAGE AS THE TUBE
ROTATES. (B) DUAL-LAYER–DETECTOR CT SYSTEM. THE MORE SUPERFICIAL LAYER (MAGENTA) ATTENUATES
LOW-ENERGY PHOTONS (YELLOW LINES) AND ALLOWS THE HIGHER-ENERGY PHOTONS (ORANGE LINES) TO
PASS THROUGH TO THE DEEPER DETECTOR (BLUE). (C) DUAL-SOURCE CT SYSTEM. TWO TUBES ARE INSTALLED
AT ROUGHLY 90° ANGLES. THE SECONDARY TUBE (B TUBE) HAS A SMALLER DETECTOR, WHICH LIMITS THE FIELD
OF VIEW AVAILABLE (SMALLER DOTTED CIRCLE IN CENTER OF ROTATION) FOR DUAL-ENERGY ANALYSIS.

8. ROLE OF IMAGING IN GI BLEEDING
• It is complementary to the endoscopic testing
• Appropriate radiology test to order depends upon
- the presumed location-upper GI, small bowel or colonic bleed.
-patients hemodynamic status and
- severity of bleeding

9. Society of Abdominal Radiology GI Bleeding-Focused Panel-
divides DECT protocol into two populations
-Overt GI Bleeding (identify-contrast material extravasation,
intraluminal clot or the cause of bleeding)
-Occult GI Bleeding (identify the source of bleeding)

10. • Overt GI bleeding –Single Energy Multiphase CT angiography
with IV contrast( no positive oral contrast)- No alternative
available
• Occult GI bleeding- ( IV contrast and oral neutral )- Single
energy Multiphase CT Angiography & Dual Energy CT

11. ADVANTAGE OF DECT OVER SINGLE ENERGY CT
• DECT has ability to replace true non-contrast series by virtual
reconstruction (VNC) reducing the dose by 19% to 50% depends
upon the number of phases in protocol and increases contrast to
noise ratio
• Perfect anatomical alignment and details-VNC images
• Increased conspicuity of subtle extravasation of the contrast
material and small enhancing bowel lesions on virtual
monoenergetic low kilo-electron voltage (40-60 keV)
• Iodine Maps(low energy) are beneficial in case of Small volume or
Subtle contrast extravasation into the hyperattenuating luminal
hemorrhage

12. ADVANTAGES
• High-kilo-electron Voltage (keV)energy reconstruction can be used
to suppress streak artifacts from metals like orthopedic implants ,
clips and coils
• This relevant if the bleeding source is near metallic surface like coil
or clip
• Better visualization of the normal and abnormal structures
obscured by streak artifacts.
• Quality images can be achieved by lower dose of intravenous
contrast( dose can be reduced to 1/2nd to 1/3rd)

13. INTERPRETATION OF DECT
IMAGES
Figure 3. Flowchart shows proposed
interpretation algorithm for overt GI
bleeding.

14. • Figure 4. Differentiation of active contrast
material extravasation, sentinel clot, and
hyperattenuating enteric contents on
VNC images in two patients with
hematochezia. (A–D) Axial arterial phase
(A) and VNC (B) CT images of the
ascending colon in a 64-year-old woman
show a hyperattenuating focus (arrow in
A) that is not present in B, which is
consistent with contrast material
extravasation. (C, D) Axial arterial phase
CT (C) and VNC (D) images show the
hyperattenuating focus (arrow) as less
hyperattenuating than
• the vasculature (C) and present on the
VNC image (D), which indicates that it is
a sentinel clot. At the time of follow-up
colonoscopy (not shown), the bleeding
had ceased, and no cause could be
identified. (E, F) Axial arterial phase CT
(E) and VNC (F) images of the ascending
colon in a 68-year-old woman show a
hyperattenuating focus (arrow), indicative
of hyperattenuating enteric contents and
not active contrast material
extravasation.

15. Meckel diverticulum that was confirmed at surgical
resection in a 68-year-old man with a history of
recurrent hematochezia and active bleeding. Axial
dual-energy CT angiography image (left) shows
hyperattenuation in an outpouching (white arrow)
arising from the distal ileum and a small focus of active
bleeding (yellow arrow). Axial 60-keV venous phase CT
(middle) and VNC (right) images show that the
outpouching (arrow) does not change in size, shape, or

16. • Similar appearance and diagnostic utility of true noncontrast and VNC images in a 66-year-old man with 2 days of bright red
bleeding from the rectum and diarrhea. Axial arterial phase (far left) image shows hyperattenuating foci (arrow) in the
ascending colon, which could be concerning for active bleeding. However, these are also present on noncontrast CT images
(center two images) and barely visible on the iodine map (far right). There is no appreciable difference in the true and virtual
noncontrast images. Calcium has an attenuation curve between that of iodine and soft tissue, so it is partially represented on
virtual noncontrast images and iodine maps. Interpretation of both images in tandem can afford accurate diagnosis.

17. SUBTLE GI BLEED IN A 68-YEAR-
OLD MAN WITH BRIGHT RED
BLEEDING FROM THE RECTUM.
(A–C) AXIAL TRUE
NONCONTRAST CT IMAGE (A)
DOES NOT SHOW THE SUBTLE
HYPERATTENUATING FOCUS
(ARROW IN B AND C) THAT
APPEARS ON THE ARTERIAL
PHASE (B) AND PORTAL
VENOUS PHASE (C) IMAGES.
THIS FINDING IS COMPATIBLE
WITH AN ACTIVE GI BLEED. (D,
E) AXIAL 40-KEV VIRTUAL
MONOENERGETIC IMAGE (D)
AND IODINE DENSITY MAP (E)
SHOW INCREASED
CONSPICUITY OF THE
HYPERATTENUATING FOCUS
(ARROW IN D AND E). THE
DIAGNOSIS WAS CONFIRMED
AT COLONOSCOPY.

18. Bowel ischemia in a 60-year-old woman with advanced atherosclerotic disease who presented with bright red
rectal bleeding, which was diagnosed as ischemic colitis on the basis of the iodine map. Axial linear blended portal
venous phase CT image (left) shows mild asymmetric attenuation (arrows) in the descending colon, although the
wall is suboptimally assessed due to underdistention. Axial 50-keV virtual monoenergetic CT image (center) does
not show increased conspicuity of the bowel wall (arrows), and the iodine map (right) shows a nearly complete
absence of iodine in the colonic wall (arrows), which is consistent with colonic ischemia and was confirmed at
colonoscopy.

19. Small
Small bowel bleeding in a 74-year-old man who was evaluated 4 years earlier for iron-deficiency anemia with
esophagogastroduodenoscopy, colonoscopy, and video capsule endoscopy and found to have a gastric
gastrointestinal stromal tumor and colonic leiomyoma, with persistent anemia. (A–C) Axial triphasic CT
enterography images show an endophytic mass (arrow) in the ileum, with nearly identical attenuation on
arterial (A), enteric (B), and delayed (C) phase images. (D–F) Axial dual-energy material decomposition virtual
noncontrast CT image (D), iodine map (E), and 50-keV virtual monoenergetic CT image (F) show iodine
enhancement in the lesion (arrow), confirming that this is an enhancing mass. The mass was surgically
resected and found to be an inflammatory fibroid polyp.

20. Jejunal metastatic melanoma in a 71-year-old man with a history of back melanoma who was thought to be in
remission after undergoing im- munotherapy and who presented with iron-deficiency anemia. Upper and lower
endoscopy (not shown) did not reveal a source. Video capsule endoscopy (not shown) showed a small bowel
hematoma in the ileum but no active bleeding or source. Axial (left and center) and sagittal blended (right) single-
phase dual-energy CT enterography images show an enhancing small bowel mass (white arrow, left and center),
causing nonobstructive enteroenteric intussusception (blue arrow, right), without upstream bowel dilatation. Jejunal

21. Diagnosis of GI bleed at single-phase dual-energy CT in a 60-year-old man with acute abdominal
pain. Single-phase CT angiography image (A) shows a hyperattenuating focus (arrow in A) in the
lumen of the ascending colon, which is not present on the VNC image (B) but is present (arrow in C)
on the iodine map (C). Active contrast material extravasation in an area of angiodysplasia was
confirmed at catheter angiography.

22. Active bleed in an 83-year-old man with abdominal pain and rectal bleeding. (A) Axial single-phase DECT
image obtained during the portal venous phase shows contrast material extravasation in a left colonic
diverticulum (arrow). (B) VNC CT image does not show extravasation, which confirms the diagnosis of active
bleeding rather than debris. (C) Iodine map shows more pronounced contrast material extravasation (arrow).

23. • Painless intermittent
hematochezia and syncope
for 1 week in a 72-year-old
man. Late venous phase
(approximately 80-second
delay after bolus initiation)
high–kiloelectron voltage (A),
low–kiloelectron voltage (B),
iodine map (C), and VNC (D)
CT images show active
extravasation (arrow in A—
C) in the right colon at the
base of a diverticulum, which
is more conspicuous on the
low–kiloelectron voltage
image (B) and the iodine
map (C) than it is on the
high–kiloelectron voltage
image (A).

24. Increased small vessel conspicuity on low–kiloelectron voltage images in an 87-year-old woman. Axial
single-energy 140-kV CT image (left) shows ill-defined soft tissue (arrows, left) between the stomach and
the pancreatic tail, but it is unclear if it is originating from the pancreas or the stomach. Axial dual-energy
65-keV monoenergetic image (right) shows a mass originating from the gastric cardia and a branch of the
left gastric artery feeding the mass (arrow, right), allowing this mass to be localized as of gastric origin.
Endoscopic biopsy results confirmed this lesion to be gastric adenocarcinoma. Low–kiloelectron voltage
increased small vessel conspicuity.

25. Reduction of streak artifact on high–kiloelectron voltage CT images. Axial linear blended portal venous phase CT
image (left) shows degradation due to a streak artifact emanating from residual concentrated enteric contrast
material in the descending colon from prior fluoroscopy. Virtual monoenergetic 200-keV image (right) shows a
diminished streak artifact, although iodine conspicuity is also decreased.

26. • Persistent hyperattenuation on iodine density CT image. Axial virtual noncontrast CT image (left),
iodine density map (center), and conventional reconstruction CT image (right) show
hyperattenuating material (arrow) in the ascending colon. The persistence of the hyperattenuating
material on the virtual noncontrast image (left) confirms that it does not represent iodinated
contrast material.

27. CONCLUSION
• DECT has tremendous value in the evaluation of GI
bleeding.
• DECT offers the ability to eliminate the noncontrast
acquisition from a multiphase CT examination for overt
or occult GI bleeding, thereby affording significant
reduction in the radiation dose.
• Additional postprocessing techniques including
reconstructing iodine maps, color iodine overlay
images, and
• low–kiloelectron voltage virtual monoenergetic images
can increase the conspicuity of contrast material
extravasation, thereby improving the diagnostic
confidence of the radiologist and assisting with problem
solving.