Application of dect in emergency radiology including the application in diagnosis of renal calculi, bone marrow edema, gout , abdominopelvic imaging,detection of pulmonary embolism and in cardiac imaging.

1. DUAL ENERGY CT IN
EMERGENCY
RADIOLOGY
DR.(PROF.) SACHIN KHANDURI
HOD, DEPARTMENT OF RADIODIAGNOSIS
ERA’S LUCKNOW MEDICAL COLLEGE, LUCKNOW

2. DECT : INTRODUCTION
 Dual energy CT or “Spectral Imaging” methods were first
investigated by Alvarez and Macovski in 1976
 In 1987, the first medical computed tomography (CT) system
with the ability to acquire dual-energy (DE) data was
commercially introduced (SOMATOM DRH)

3.  However, its major utility has been established in the last
decade due to its greater speed and lesser noise and
simultaneous acquisition of data of 2 different energies.

4. WHAT IS DUAL ENERGY CT AND
WHAT CAN IT TELL US?

5.  The principle of dual energy CT is based on- differential absorption of
energy(Linear attenuation coefficient) at variable KVP settings
 Two main mechanisms: Compton scatter and Photoelectric effect
 Compton effect is energy independent
 Photoelectric effect is strongly energy dependent. It is the ejection of
electron from K shell of the atom.
 Changing the kV setting results in an alteration of photon energy
When incident photon has sufficient
energy to overcome K shell binding
energy, photoelectric effect occurs.

6. PHOTOELECTRIC EFFECT

7. The closer the energy level to the K edge of a substance, the
more the substance attenuates.

8.  The two energies most frequently employed are 80 kVp and 140
kVp. Because the K edge of iodine (33.2 keV) is closer to 80 kVp
than it is to 140 kVp, the attenuation of iodine-containing
substances is substantially higher at 80 kVp
 Dual-energy CT is used to distinguish substances such as iodine,
calcium, and uric acid crystals from soft tissues.

9.  Knowing how a substance behaves at two different energies can provide
information about tissue composition beyond that obtainable with single-energy
techniques
Increased attenuation of iodine-containing structures on lower-energy images. (a) Axial contrast enhanced
portal venous phase CT image obtained at 80 kVp with a 26-cm field of view shows that iodine containing
structures, such as the main portal vein and kidneys, have high attenuation at 80 kVp, which is close to
33.2 keV, the K edge of iodine. (b) Axial contrast-enhanced portal venous phase CT image obtained at 140
kVp shows that iodine-containing structures have lower attenuation as the beam energy moves farther
away from the K edge of iodine.
𝑎 𝑏

10. WHAT CAN DUAL-ENERGY CT TELL
US?
 Dual-energy CT provides information about
: how substances behave at different energies
: the ability to generate virtual unenhanced datasets
:improved detection of iodine-containing substances on low- energy images

11. BASIS OF DUAL ENERGY CT
1. ENERGY DEPENDENCE OF PHOTOELECTRIC EFFECT
2. VARIABILITY OF K-EDGES OF DIFFERENT SUBSTANCES

13.  Conventional DE CT  DE with Tin Filter (Selective Photon
Shield)
• Significant spectral overlap
• Limits energy separation
• Limits dose efficiency
• Minimized spectral overlap
• Increased energy separation
• Complete dose neutrality
Dual Source Dual Energy with
SOMATOM Force

15. RADIATION DOSAGE IN DUAL
ENERGY CT
 Radiation exposure for DECT depends on the type of approach
 Ho et al.,[12] showed two to three times higher doses for DECT based on
single source rapid voltage switching technique
 In dual source scanners, the tube currents can be adjusted to low levels so
that the radiation exposure is similar to that of single energy CT
 Low Kvp Better iodine attenuation

16. Virtual non contrast imaging reconstruction reduced the total effective dose of
multiphase DECT imaging by 19% to 28%.
DECT exposes the patient to excessive radiation; however, it is way less than
100-200mSv, the proposed values below which there is no statistical
significance of increased risk of radiation induced malignancy
RADIATION DOSE DUAL ENERGY CT SINGLE ENERGY CT
CTDI(vol) 49.4 mGy 16.2 mGy
Effective dose 22.5 to 36.4 mSv 9.4 to 13.8 mSv
RADIATION DOSAGE USING ABDOMINAL PROTOCOL

17. TECHNICAL APROACHES TO DECT
 Five approaches : (currently only former three are commercially
available)
 Sequential acquisition
 Rapid voltage switching
 Dual Source CT
 Layer detectors
 Energy resolving or quantum counting detectors

18. SEQUENTIAL ACQUISTION RAPID VOLTAGE SWITCHING DUAL SOURCE CT
Requires least hardware effort.
Can be achieved as
• two subsequent helical scans
• sequence with subsequent
rotations at alternating tube
voltages and stepwise table
feed.
• Tube voltage alternates
between a140kV and 80 kV
• Data are collected twice for
every projection.
• Two tubes running at different
voltages
• Corresponding detectors
mounted orthogonally in one
gantry.
Disadvantage is rather long delay
between both acquisitions,
causing artifacts from cardiac or
respiratory motion
The advantages are good
temporal registration between
high- and low-energy datasets
High-energy scans are obtained
at 120 or 140 kVp, and low-
energy scans are obtained
simultaneously at 80 or 100 kVp

19. DUAL SOURCE CT SCANNER

20. SOMATOM Force @ ERA Medical College,
Lucknow
 SOMATOM Force
 16 Dual Energy classes
 30% better spectral separation with Tin
Filter (Selective Photon Shield II)
 Dose neutral Dual Energy
 Dual Energy at high scan speeds (~285
mm/s1))
 Increased FoV (35 cm)

21. APPLICATIONS OF DUAL ENERGY
CT IN EMERGENCY RADIOLOGY

22. APPLICATION OF DUAL ENERGY
CT IN RENAL IMAGING
 Potential applications include
- ability to distinguish hyperattenuating renal cysts from renal cell
carcinoma
- identification of renal calculi and characterization and volume estimation
of renal calculi.
 In addition, by use of the DECT technique, calculi are detectable on
nephrographic phase imaging or in contrast filled collecting systems
using iodine substraction technique
 Allows better characterization of renal and ureteric stones than with
single-energy CT

23. By using the postprocessing techniques described by Boll et al (19), a renal calculus with
attenuation values of 825 HU at 140 kVp and 1250 HU at 80 kVp was determined to be
composed of calcium oxalate monohydrate
Characterization of a renal calculus with dual-energy techniques. Dual-energy axial CT images show a left renal
calculus with attenuation of 825 HU at 140 kVp (a) and 1250 HU at 80 kVp (b). The calculus was determined to be
composed of calcium oxalate monohydrate with the use of postprocessing techniques (c).

24. Fig.A-E, Two patients presenting with left flank pain underwent DECT at 120 kvp and 140 kvp
for nephrolithiasis.

25. Fig.F and G, A 40-year-old man who presented with left flank pain. Coronal (F) and axial (G)
unenhanced DECT images show calcium-containing stone in left upper pole.

26. DECT to differentiate urinary renal stone composition.
Red color indicates that the calculus consists of uric acid

28. MUSKULOSKELETAL
APPLICATION OF DUAL ENERGY
CT  APPLICATION IN ACUTE GOUT
 DECT can reveal the presence of monosodium urate (MSU) crystals in and
around joints in gout arthropathy with visualization of MSU crystals.
 This is the most notable application of DECT in musculoskeletal imaging.
 DECT as a sensitive, specific, and non invasive means of diagnosing gout
and is clinically valuable in the acute setting in comparison to microscopic
aspiration from joint.

29.  Due to high specificity of DECT for confirmation of MSU crystals in
calcium, the automated calculation of MSU crystal volumes within a
tophus is possible.
 Excellent sensitivity and specificity (100% for both) were also reported
for the detection of tophaceous gout.
 DECT is four times more efficacious in identifying urate deposits
compared with the clinical examination. This finding suggests the
possibilities of application of this method for monitoring the disease
course

30. Figure 1: (a) A 28-year-old man with
gout depicting monosodium urate
crystal deposition in the left knee joint
on dual energy computed tomography.
MSU crystals appear Green

31. (b) Volume-rendered color-coded
image of both the knee joints
depicts presence of monosodium
urate crystals in periarticular soft
tissue of the left knee joint (arrow).

32. Fig. H and I, A 45-year-old woman with suspected gout on x-ray.

33. A 56-year-old man who presented
with either osteomyelitis or acute
attack of gout along first
metatarsophalangeal (MTP) joint;
condition was eventually diagnosed
as gout on dual-energy CT (DECT

34. C and D, Volume-rendered image from DECT (C) and sagittal two-material
decomposition multiplanar reformatted color-coded image (D) show presence of
gouty monosodium urate tophi in green (arrows) with erosions at first
metatarsophalangeal joint, midfoot, and ankle of right foot definitively confirmed.

35. APPLICATION OF DECT IN METAL ARTIFACT
REDUCTION
 Imaging of patients with metal hardware artifacts with CT remains a
challenge despite techniques devised to overcome this problem
 Current techniques to reduce metal artifact include increasing the peak
kilovoltage.
 Recent literature has suggested the use of the monoenergetic spectral
beam of DECT as a method to eliminate the reconstruction error.

36. A 30-year-old man with open reduction and internal fixation of the head and the neck of right
humerus. Shown are coronal dual energy computed tomography images reconstructed using
monoenergetic spectrum application on a multimodality workstation.

37. Dual Energy: Tibia with metal artifact
reduction

38. Fig- A 34 year-old-man who
was injured in a bombing
accident.
Axial dual-energy CT images
acquired at 100 kV (C) and 120
kV (D) show substantial
reduction in metallic streak
artifact, allowing specific
localization of fragment in right
atrium

39. APPLICATION OF DECT IN ASSESSMENT OF
MUSKULOSKELETAL TARUMA
1.ASSESSMENT OF BONE MARROW EDEMA
 Bone marrow edema is best visualized with MRI techniques, appearing
as hypointense on T1 and hyperintense on T2 weighted images.
 Recent studies have shown evaluation of traumatic bone marrow
edema using a DECT virtual non–calcium- subtraction technique.
 It allows the subtraction of calcium from cancellous bone, allowing the
identification of bone marrow edema.

40. —79-year-old woman with subtle insufficiency fracture
and surrounding bone marrow edema. A, Insufficiency
fracture (arrow) is noted in proximal medial tibia that is
not easily visible on plain anteroposterior radiograph
of knee

41. B and C, Dual-energy CT coronal (left panel, B) and axial (left panel, C) virtual non–calcium-subtracted images
and corresponding color-coded three-material decomposition (calcium, fat, and water) images (right panels)
show presence of subchondral bone marrow edema at medial femoral condyle and proximal medial tibial
plateau as high attenuation on virtual unenhanced images (arrows, left panels) and as dense blue on color
coded images (arrows, right panels)

42. Fig 2: Axial (a) source Dual-
Energy CT bone window
and (b) gray-scale virtual
noncalcium images with (c)
corresponding T2-weighted
MR image of posttraumatic
bone bruises in the
posteromedial and
posterolateral tibial plateau.
Although edema appears
subtle on the gray-scale
virtual noncalcium image (b)
the bone bruises become
obvious on the color-coded
virtual noncalcium image
(d).
𝑎 𝑏
𝑐
d

43. AREA SHOWING BONE
MARROW EDEMA IN A
PATIENT OF TRAUMA

44. 18-year-old female with vertebral compression fracture and bone edema. Cross-sectional (sagittal and coronal)
color-coded three-material decomposition (water, fat and calcium) images obtained using virtual noncalcium
technique show collapse of L1 vertebral body with presence of bone marrow edema (arrow) as high attenuation
area appearing dense green. The region of interest (arrow) shows high mean HU value as compared to the normal
(as indicated in L2 vertebra), indicating bone edema.

45. [A] Sagittal MPR image with color-
coded tendons. Note the interruption
of the extensor hallucis longus tendon
[B] Axial MPR image. Note the color-
coded flexor and extensor tendons
and the absent first extensor.
[C] Volume-rendered image from a
superior view showing the extensor
tendons and the interrupted hallux
tendon.
[D] VRT in a plantar view showing the
flexor tendons.
2.TENDON AND LIGAMENT
INJURIES

46. [A] + [B] Volume-rendered images
showing the continuity of the flexor
tendons
[C] + [D] Color-coded
reconstructions in coronal and
sagittal orientation
45-year-old female patient was referred
for diagnostic workup of chronic pain in
the wrist six years after an intraarticular
fracture of the radius.
NO LIGAMENT TEAR WAS SEEN

47. VASCULAR AND AORTIC APPLICATIONS
OF DECT
 Recommendation of:
low-peak-kilovoltage images and mixed images in DECT interpretation of aorta
 The standard CT arteriography protocol for the assessment of acute aortic
syndromes includes unenhanced images to detect hyperdense intramural
hematoma or intimal calcifications and to detect dissection
Increase radiation exposure
Although virtual unenhanced images are slightly noisier compared with
unenhanced images, they are diagnostic in almost 95% of cases

48.  It has been shown that both attenuation measurements and image
noise for virtual unenhanced images are equivalent to those for genuine
unenhanced images and could replace these images, saving radiation
dose
 By use of DECT, faster removal of calcified plaques in large arteries and
bony structures in the cranial region is possible

49. 75-year-old woman who underwent calcific plaque and bone removal. A and B, Coronal dual-
energy abdominal CT angiography images show detection of calcific plaques (pink areas) in
abdominal aorta and external iliac arteries (A) by plaque removal protocol; these areas are
removed from arteries in panel B

50.  The precise removal of calcium from arteries assists in better
evaluation of atherosclerotic arteries
 LIMITATION-The increases in radiation dose, noise, and small
diameter of the distal peripheral arteries are limitations for
dual-energy peripheral CTA
 SOLUTION-High-resolution dual-energy acquisitions
combined with iterative reconstruction and spectral filtering can
be a solution to this problem

51. 92-year-old man with prior
aortic graft repair and
known endoleak.
Dualenergy CT (DECT)
has benefits for artifact
reduction and vascular
imaging in patients with
graft repair.

52.  DECT can detect endoleaks in a single acquisition and obviates unenhanced
CT images and thus reduces the radiation dose to patients who have to
undergo lifelong follow-up examinations after endovascular aneurysm repair
 Low-peak-kilovoltage imaging helps identify subtle enhancement, such as
endoleaks within the endovascular stent aortic repairs

53. Dual-energy CT images using low-contrast-dose (50 mL) dissection protocol show adequate
enhancement of aorta with postsurgical changes from infrarenal abdominal aortic repair with large
aneurysmal sac diameter

54.  In addition, DECT has benefits for metal artifact reduction in vascular imaging of
patients with graft repair
 Contrast is increased in low peak kilovoltage images as compared to high peak
kilovoltage images, and the increase in iodine attenuation is an advantage of low
peak kilovoltage CT arteriography
Reduced contrast utilisation and less radiation

55.  The delayed phase of the scan depicts endoleaks with higher sensitivity
because it reveals endoleaks that cannot be visualized during the arterial phase
 a significant dose reduction is achievable by eliminating the unenhanced and
arterial phases
 With the rapid peak-kilovoltage-switching method, the derived 50-keV
monochromatic images with lower energy increase attenuation, and the
acceptable image noise optimally shows low enhancement levels, such as in
subtle endoleaks

56. Iodine analysis image shows robust contrast enhancement of aorta, allowing low-dose examination. E and F, Axial
image from monochromatic series at 50 keV (F) increases contrast of image and relative enhancement of aorta in
Hounsfield units when compared with standard algorithm at same level (E).

57. DECT IN PULMONARY EMBOLISM
 Capability of DECT to use diagnostic information available from both 80-
and 140-kVp energy levels optimizes :
1. Contrast-to-noise ratio within pulmonary vessels
2. facilitates detection of peripheral endoluminal clots compared with
images acquired at high energies
 The low-energy acquisition allows generation of images with increased
vascular enhancement. In addition, because of the feasibility of
reconstruction at intermediate energy levels (90–130 keV), optimal
contrast for visualization of an endoluminal clot can be obtained

58. DECT Perfused Blood Volume map generation

59.  Two categories of scans—diagnostic scans and lung perfusion scans—
are routinely reconstructed by DSCT.
 The diagnostic scans typically consist of contiguous 1-mm-thick
transverse CT slices that are generated by combining the raw spiral
projection data of both energy levels.
 The DECT technique can generate three series of images:
1. the native perfusion scans
2. maximum intensity projections of lung perfusion
3. fused images that combine the native perfusion scan and the diagnostic
scan.

60.  With a DECT technique, perfusion defects beyond obstructive clots
can be identified using perfusion scans
Acute pulmonary embolism

61. ACUTE PULMONARY EMBOLISM

62. PERIPHERAL EMBOLI

63. Correlation of perfusion deficits in a 20-year-old male and 42-year-old female male with pulmonary embolism
(arrows pointing to perfusion defects). A, D: Dual-energy computed tomography derived iodine map; B, E:
Pulmonary blood flow; C, F: Pulmonary blood volume.

64. 60-year-old man with chest pain. A–C, Coronal virtual unenhanced (A), iodine map (B), and perfusion (C) dual-
energy CT images show mass at right upper lobe bronchus and decreased perfusion in right upper lobe.

65. A 45-year-old woman with chest
pain and bilateral multiple
thromboemboli. A–C, Dual-energy
coronal (A and C) and sagittal (B)
perfusion images show bilateral
decreased perfusion (dark blue
areas) in right upper and lower
lobe and left lobes compared with
areas with normal perfusion (light
blue areas). D and E, Curved planar
maximum-intensity projection
images show emboli in right (D)
and left (E) inferior pulmonary
arteries.

66. APPLICATION OF DECT IM MYOCARDIAL ISCHEMIA
 According to the literature, 68–92% sensitivity and 93% specificity have been reported
for DECT, compared with SPECT, for the detection of myocardial perfusion defects
 The superior spatial resolution of CT compared with SPECT allows the detection of
smaller, especially subendocardial, areas of severe ischemia or infarction that are not
detectable on rest SPECT
 In addition, the iodinated contrast medium used in CT has a vasodilatory effect, which
may cause hyperemia similar to the response to vasodilator drugs used in myocardial
perfusion imaging

67. FLOWCHART DEPICTING CARDIAC
PROTOCOL OF DUAL ENERGY CT

68. G, Volume-rendered dual-energy CT
image shows perfusion defect of
anterior left ventricle wall within
context of entire thorax.

69. 45-year-old man with recent
infarction of inferior left
ventricle wall and stent in
right coronary artery (RCA),
undergoing dual-energy CT
and SPECT before coronary
artery bypass grafting. A and
B, Coronary CT angiography
images, including volume-
rendered reconstruction (A)
and multiplanar reformatted
reconstruction (B), show
long segment of occlusion in
proximal left anterior
descending artery (LAD)
(arrow, A), and patent stent in
RCA (arrow, B). C and D, On
SPECT horizontal stress (C)
and rest (D) long-axis
images, there is reversible
perfusion defect of
anteroseptal wall (arrows, C).
E and F, Corresponding
views for stress (E) and rest
(F) dual-energy CT show
reversible perfusion defect of
anteroseptal wall (arrows, E)

70. DUAL-ENERGY CT APPLICATIONS IN INTRACRANIAL
HEMORRHAGE
 DECT may be used for differentiating a hyperdensity arising from intracranial
hemorrhage from that arising from iodine extravasation or staining.
 DECT can distinguish the two on the basis of the different spectral signatures
of blood and iodine.
 Differentiating contrast agent from hemorrhage in this early period has
important implications in clinical decision making.

71.  All the hyperattenuated lesions were analyzed and classified as
:1.haemorrhage 2.contrast 3.combination of the two
 Based on the VNC and iodine overlay images.
 A hyper-attenuation only seen on the VNC image was classified as
haemorrhage
 A hyper-attenuation only seen on the iodine overlay image was deemed as
contrast.

72. Subarachnoid hyperattenuation due to hemorrhage in a 64-year-old man. A, There
are foci of sulcal hyperattenuation (arrows) on the SE image. B, No corresponding
hyperattenuation is seen on the iodine overlay image. C, VNC image shows
identical foci of sulcal hyperattenuation, suggesting subarachnoid hemorrhage that
was confirmed by the 24-hour follow-up NCCT (D).

73. Left thalamic intraparenchymal hyperattenuation due to haemorrhage of uncertain etiology in a 51-year-old man
referred for altered mental status
(A) SE image shows left thalamic intraparenchymal hyperattenuation without corresponding hyperattenuation on
the iodine overlay image (B).(C) The focus of hyperattenuation is well demonstrated on the VNC image. A 24-hour
follow-up NCCT scan (D) demonstrates largely stable hyperattenuation in the left thalamus, with an increase in the
surrounding edema, confirming the original diagnosis of intraparenchymal hemorrhage

74. DECT IN DETECTING ACUTE PANCREATITIS
 In the diagnosis of acute pancreatitis, conventional contrast-enhanced CT
images show hypo-enhancement of the pancreatic tissue –
 This signifies i) severe ischemia &/or
ii) Frank infarction and necrosis
 However, iodine material–density DECT images can distinguish between the
two entities and contribute to the display of hypoperfusion area around the
necrosis
 The water material–density CT display has been reported to be useful in
distinguishing enhancing pancreatic parenchyma as a result of acute
haemorrhage.

75. DECT in imaging of pancreatic lesions.
• Another advantage of imaging the pancreas with DECT is the median position of the pancreatic
gland in the abdomen

76. CONCLUSION
 Dual-energy CT provides information about
:how substances behave at different energies
: the ability to generate virtual unenhanced datasets
:improved detection of iodine-containing substances on low-energy
images
 Promising for improved detection and characterization of lesions in the
abdomen and pelvis and for evaluation of vascular structures
 Reductions in radiation dose are possible with dual-energy CT if the need for
true unenhanced datasets is eliminated

77. THANK YOU