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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3676_Библиотеки_им_академика_М_И_Перельмана
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Fig. 14.57 80 KVp technique with 25 mL contrast: 3D
Volume rendered image of aorta with reference levels
T.A. Hameed
Fig. 14.58 Tricuspid aortic valve with calcification
Fig. 14.59 80 KVp technique with 25 mL contrast. 3D
Volume rendered image of aorta and iliac arteries
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14.7.2 CT Technique
Timing run 1: 1 mL@3.5/s, saline push 20 mL@3.5/s:
22 s
Timing run 2: 2 mL@3.5/s, saline push25mL@3.5/s:
31 s
CT scanner: 4 cm long detector array, 128- channel
MDCT
Scan coverage: Aortic arch to common femoral
arteries (Single scan acquisition)
KVp 80
mAs 1260
Scan time 25 s
Scan delay 28 sec
Contrast Injection: 25 mL (10 mL@3/s +
15 mL@2/s) + saline push 30 mL@2/s
Images demonstrate diagnostic quality examination with enhancement density > 200 HU in the
aortic root and iliac arteries (Figs. 14.50 and
14.51). Images acquired in standard locations
and planes demonstrate aortic annulus with effective diameter of 28.4 mm. There is a trileaflet
valve with moderate calcifications..
The patient was treated by implantation of
29 mm Sapien 3 valve via transfemoral approach
(Fig. 14.60). Chest radiograph after TAVR demonstrates the prosthetic valve in place (Fig. 14.61).
Fig. 14.60 Fluoroscopy image during placement of
29 mm Sapien 3 valve via transfemoral approach
Fig. 14.61 Chest radiograph with transcatheter heart
valve in place
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T.A. Hameed
14.7.3 Diagnosis
CTA for pre-TAVR planning with low contrast
dose with good diagnostic quality.
14.7.4 Discussion
The risk of CIN must be considered relative to the
potential benefits of the contrast enhanced examination. The risk of CIN is higher with larger contrast dose and the CTA examination may thus be
obtained with as low a contrast dose as possible.
The goal is to attain adequate contrast enhancement in the aorta and iliac arteries. For a given volume of contrast, the attenuation is higher with
80 KV compared to 120 KV. The contrast enhancement in blood vessels also depends on the volume
and concentration of iodinated contrast. Use of
bolus timing run helps in determining contrast
arrival time and expected peak enhancement to
determine appropriate time to scan (scan delay).
With standard bolus triggering technique, there is
a variable scan delay for the scanner to get ready to
scan, usually around 4–5 s, requiring a larger volume of contrast to be injected. Bolus timing run to
determine the time of contrast arrival can be used
to plan the start of injection more accurately without the need for scan delay after bolus triggering.
14.7.5 Pearls and Pitfalls
The contrast injection duration is selected to be
close to the scan duration. In order to achieve
higher attenuation in the aorta, the time to begin
CT scanning after contrast injection (scan delay)
should be near the end of contrast bolus train, i.e.,
contrast bolus arrival time + injection duration.
Due to overall higher attenuation achieved with
80 KVp, injection rate can be slower (~2 mL/s)
compared to 4–5 mL/s otherwise used with
120 KVp imaging. Biphasic injection (3–3.5 mL/s
followed by 2 mL/s) can be useful in achieving a
higher initial attenuation which is sustained by a
slower, longer injection for scan duration.
14.8 Case 7
14.8.1 History
An 85-year-old with severe symptomatic aortic
stenosis and decreased renal function; for preTAVR evaluation CT with low contrast dose.
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14.8.2 Findings
ECG-gated helical CTA examination of the chest,
abdomen, and pelvis performed with total contrast volume of 34 mL with 80 KV technique
(Figs. 14.62, 14.63, 14.64, 14.65, 14.66, 14.67,
14.68, 14.69, 14.70, 14.71, 14.72, 14.73, 14.74,
and 14.75).
Scout image demonstrates a large patient with
transverse diameter of greater than 500 cm at the
level of pelvis (Fig. 14.62).
The examination was performed with 80 KVp
on 8 cm long MDCT detector array (256-slice
128-channel) CT scanner. Two bolus timing runs
using 1 and 2 mL in ascending aorta and in femoral arteries demonstrate time of contrast arrival at
17 s and 23 s, respectively (Figs. 14.63 and
14.64).
Two separate sets of CT images through the
chest (ECG gated) (Figs. 14.65, 14.66, 14.67,
14.68, 14.69, and 14.70) and abdomen/pelvis
(Figs. 14.71, 14.72, 14.73, 14.74, and 14.75)
(without ECG gating) were acquired using 15 mL
for chest and 16 mL for the abdomen and pelvis,
respectively. CTA images through the chest are of
adequate quality showing the aortic annulus area
of 584 mm2 (Fig. 14.70). There is moderate calci-
fication in the aortic valve (Fig. 14.69). 3D VR
image shows no significant tortuosity of thoracic
aorta (Fig. 14.70).
The CTA images through lower abdomen and
pelvis (Figs. 14.71, 14.72, 14.73, and 14.74)
demonstrate good diagnostic quality with normal
size of aorta and iliac arteries without significant
plaque or tortuosity (Fig. 14.75).
Fig. 14.62 Scout radiograph—transverse diameter of
greater than 500 cm at the level of pelvis
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T.A. Hameed
Fig. 14.63 80 KVp, 1 mL contrast. Timing run—in ascending aorta
Fig. 14.64 80 KVp, 2 mL contrast. Timing run—in femoral arteries
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Fig. 14.65 Oblique coronal view for selection of aortic
annulus plane
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Fig. 14.67 KVp 80, mAs 1650, ECG gated: 15 mL contrast for chest. Aortic valve annulus
Fig. 14.66 Oblique sagittal view for selection of aortic
annulus plane
Fig. 14.68 Aortic annulus area measured with annulus
area of 583.75 mm sq
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Fig. 14.69 Aortic Valve with moderate calcification
T.A. Hameed
Fig. 14.71 80 KVp, 16 mL contrast for abdomen and
pelvis: axial image, infrarenal aorta, metallic hardware in
spine
Fig. 14.70 80 KVp, 15 mL contrast. 3D VR: thoracic
aorta
Fig. 14.72 Axial image: Adequately enhanced common
iliac arteries
Fig. 14.73 Axial image: Adequately enhanced external
iliac arteries
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Fig. 14.74 Axial
image. Adequately
enhanced femoral
arteries
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Fig. 14.75 KVp 80, mAs 1500, Non-gated. 16 mL contrast. 3D VR. Abdominal aorta without tortuosity and
mild to moderately tortuous iliac arteries
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T.A. Hameed
14.8.3 Diagnosis
CTA with adequate quality for pre-procedure
evaluation of TAVR with low contrast dose.
14.8.4 Discussion
The patient is of large size and has metallic hardware in the spine. Factors affecting contrast
enhancement in aorta include patient size and
there is decreased enhancement with higher body
mass index (BMI). Use of imaging with 80 KV
will increase the contrast enhancement for a
given contrast dose. However, low KV is associated with higher noise, which is to be compensated by increasing the tube current by several
fold and this can become a limiting factor particularly in large patients. ECG-gated imaging
requires even higher tube current for optimal
image quality compared to non-gated imaging. In
this case with large patient size and imaging with
80 KVp, there is high noise in the ECG-gated
images. However, as CTA utilizes high contrast
resolution, diagnostic quality can still be obtained
with relatively high noise compared to low contrast resolution needed for imaging of viscera or
other extravascular soft tissues.
For the second set of images through the abdomen and pelvis, a high tube current (1500 mAs)
was possible due to non-gated imaging over a
shorter distance (abdomen and pelvis compared
to combined chest, abdomen, and pelvis) which
is able to provide good image quality with low
noise (<25 HU) even with large patient size and
metal in spine. Adequate density of contrast
enhancement in the arteries was achieved with
only 15–16 mL contrast due to 80 KV and optimal timing using bolus timing run.
14.8.5 Pearls and Pitfalls
Image noise is decreased with higher tube current
for a given tube voltage. Newer image reconstruction techniques utilizing iterative techniques
and iterative model based reconstruction are very
helpful in reducing noise. The image noise can
also be reduced with the use of a smooth filter
(soft tissue) compared to a high resolution filter
(cardiac), which may not be necessary in case of
imaging of large vessels such as aorta.
14.9 Case 8
14.9.1 History
A 77-year-old with failed prosthetic aortic valve
and decreased renal function for pre-TAVR evaluation CT with low contrast dose.
14.9.2 Findings
CTA performed with a total of 28 mL intravenous
contrast dose using two separate image acquisitions demonstrates adequate image quality for
assessment of aortic root including the bioprosthetic valve and aorta and iliac arteries.
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14.9.3 Technique
Two timing bolus runs using 1 mL contrast each
were performed. Two separate contrast injections
using 17 mL and 9 mL contrast were used for two
separate CT imaging through chest (ECG gated)
and abdomen/pelvis (non-gated), respectively.
Timing run 1: 1 mL@3.5/s, saline 20 mL@3.5/s: 18 s
Timing run 2: 1 mL@3.5/s, saline 25 mL@3.5/s: 23 s
CTA Chest:
Helical ECG gated
KVp 80
mAs 1525
Scan time 5 s
17 mL (7 mL@3.5/s, 10 mL@2/s) + NS 30 mL@2/s
CTA Abdomen and Pelvis:
Helical non-gated
KVp 80
mAs 615
Scan time 5 s
Contrast: 9 mL (3 mL@3/s, 6 mL@2/s) + NS
20 mL@2/s
The images demonstrate adequate image quality with density of greater than 200 HU in the
aortic root (Figs. 14.76, 14.77, 14.78, 14.79,
14.80, 14.81, 14.82, 14.83, 14.84, 14.85, 14.86,
and 14.87). The density in iliac arteries is less
than 200 HU but adequate for diagnosis. There is
bioprosthetic valve in place. The virtual ring
drawn at the superior margin of the posts shows a
relatively spacious sinus with ring to left coronary artery ostium distance of 7 mm placing this
at low risk for coronary occlusion.
Fig. 14.76 80 KVp technique: Bolus timing run with 1 mL at ascending aorta with attenuation curve showing peak
enhancement at 18 s
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