Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3752_Библиотеки_им_академика_М_И_Перельмана
.pdf
326
Triple Rule-Out CTA
CTA can be used as the fi rst choice in the emergency room to
rule out aortic dissection, acute coronary syndrome, pulmonary embolism, and adjacent intrathoracic structure pathology in patients with chest pain in an appropriate clinical
setting. Triple rule-out requires an ECG-gated study. This
can eliminate further testing in 75 % of the patients and provide a cost-effective evaluation [ 19 ].
CTA Accuracy in Diagnosis of Aortic Disease
Several studies have demonstrated the accuracy of CT for the
diagnosis of aortic diseases. Hayter et al. [ 20 ] investigated
373 patients who underwent CTA in the emergency room for
suspected aortic disorders. The diagnosis of acute aortic
disorder was confi rmed using surgical/pathologic diagnoses
or any imaging as the reference standard (aortography, MRA,
or echocardiography). In total, there were 23 acute aortic
dissections, 14 acute aortic intramural hematomas, 20 acute
penetrating aortic ulcers, 44 new or enlarging aortic
aneurysms, and 11 acute aortic ruptures, and 305 cases were
interpreted as negative for acute aortic disorder. The resulting
sensitivity was 99 % (67 of 68), specifi city was 100 % (304
of 304), the positive predictive value was 100 % (67 of 67),
the negative predictive value was 99.7 % (304 of 305), and
the accuracy was 99.5 % (371 of 373). Stueckle et al. [ 21 ]
compared conventional angiography to CTA in the diagnosis
of morphologic changes in the abdominal aorta and its
branches in 52 patients who underwent both MDCT and
invasive angiography before surgical treatment. All CT
examinations were performed after the administration of
100 mL of contrast medium with a collimation of 4 × 1 mm
and a pitch of 7. All aneurysms, occlusions, stenoses, and
calcifi cations were diagnosed correctly by CTA in axial and
multiplanar projections (sensitivity 100 %; specifi city
100 %). The degree of stenosis was overestimated in three
cases when using axial projections. 3D volume-rendered
(VR) CTA showed a sensitivity of 91 % for aneurysms, 82 %
for stenoses, 75 % for occlusions, and 77 % for calcifi cations. The specifi city was 100 % in all cases.
With more detector systems, imaging improves. Multislice
CTA is similar to invasive angiography for abdominal vessels
if multiplanar projections are used. Yoshida et al. [ 22 ]
evaluated 57 individuals who underwent emergency CTA
and surgery for type A aortic dissection or intramural
hematoma. The diagnosis by CTA was correct as type A
aortic dissection (45 patients) or intramural hematoma (12
patients) according to surgical pathology. The accuracy of
CTA was 100 % (57 of 57), the sensitivity was 100 % (49 of
49), and the specifi city was 100 % (eight of eight). In addi-
tion, all values were 100 % for diagnosis of aortic arch
anomalies.
These fi ndings demonstrated that CTA is a highly accu-
rate imaging method in all kinds of thoracic and abdominal
aorta diseases. CTA produces excellent 3D images that are
competitive in quality with interventional angiography. In
some instances, CTA images can give more information
about the aortic diseases due to visualization of lumen,
thrombus, and wall disease simultaneously as compared to
interventional angiography.
Conclusion
The simultaneous acquisition of multiple thin collimated
slices in combination with enhanced gantry rotation speed
offers thin-slice coverage of extended volumes without any
loss in spatial resolution. Early limitations of four-slice
scanners required restricting the scan volume and focusing
on dedicated abdominal vessel territories in order to provide
high spatial resolution (1–2 mm). 16+ detector-row
technology now enables full abdominal coverage from the
diaphragm to the groin without compromising spatial
resolution. This technique enables the evaluation of the
Fig. 18.8 A patient status post repair of a thoracic aortic aneurysm.
The stent can be seen without scatter artifact or partial volume effect
A. Alani and M.J. Budoff
https://t.me/medicina_free
327
whole arterial visceral vasculature (e.g., hepatic vessels,
mesenteric vessels, renal arteries) and the aortic-iliac axis in
a single data acquisition. More detectors allow faster volume
coverage (and reduce the contrast requirements).
Renal CT Angiography
Important indications for directed renal artery imaging
comprise the assessment of patients with suspected renal
vascular hypertension to exclude hemodynamically
signifi cant renal artery stenosis, as well as a complete
preoperative assessment for renal transplant candidates.
Current CT systems with 64+ channels permit rapid
acquisition of large volumes of submillimeter data with
isotropic resolution (equal resolution in the X, Y, and Z
dimensions). This allows 3D data to be reconstructed in any
plane. Wide ranges of functional techniques are now
available with CTA, which may help us to identify patients
who would or would not benefi t from renal artery
revascularization [ 23 ]. CTA of the renal arteries is performed
with a high-resolution protocol (with thickness as low as
0.5–0.625 mm). Achieving adequate coverage to encompass
the entire kidneys and the origins of accessory renal arteries
is easily accomplished in a scan with a duration of <3 s, or as
part of the aortic evaluation (described previously). With
adequate selection of the acquisition parameters (thin
collimation), high-spatial-resolution volumetric datasets for
subsequent 2D and 3D reformation can be acquired
(Fig. 18.9 ). Whereas fast acquisitions allow for a reduction
of total contrast volume in the setting of CTA, this is not the
case when CTA is combined with a second-phase abdominal
MDCT acquisition for parenchymal (e.g., hepatic) imaging.
Comparison to Other Modalities
Although renal artery duplex ultrasound (US) is often the fi rst
examination performed, there are a number of well- recognized
limitations, the most important of which is the challenge of
optimally visualizing these vessels in obese patients. Catheter
angiography has been the traditional gold standard for renal
artery evaluation [ 24 ], but limitations include invasiveness of
the procedure, contrast allergy, nephropathy, and plaque
embolization. The improvements in spatial resolution and
image quality of cross-sectional techniques have allowed MR
and CTA to replace this invasive examination in most circumstances. MRA has also benefi ted from a number of recent
developments, including improvements in gradient hardware
and the recent introduction of parallel imaging, both of which
permit reduced acquisition times and improved spatial resolution. However, thicker slices with MRA require acquisition in
the plane of interest, making scanning protocols much more
complicated. Renal CTA is an accurate and reliable test for
visualizing vascular anatomy (Fig. 18.10 ) and renal artery
stenosis, and it is therefore a viable alternative to MRA in the
assessment of patients with renovascular hypertension and in
potential living related renal donors.
CTA Accuracy in Diagnosis of Renal Artery
Stenosis
Several studies investigated the diagnostic accuracy of CTA
in the diagnosis of renal artery stenosis. CTA has been
reported as having 94–100 % sensitivity and 79–97 % specifi city [ 25 ]. Rountas et al. [ 26 ] compared the diagnostic
Fig. 18.9 A volume-rendered image of the abdominal aorta and vessels (including exquisite detail of the mesenteric and iliac arteries)
using 64-detector MDCTA
Fig. 18.10 Renal artery aneurysm
18 Aortic, Renal, Mesenteric and Carotid CT Angiography
https://t.me/medicina_free
328
accuracy of renal artery duplex US, CTA, and MRA to the
gold standard, digital subtraction angiography, for the detection of renal artery stenosis in 58 patients with clinically suspected renovascular hypertension. There were 132 renal
arteries. The sensitivity and specifi city were 75 % and 89.6 %
for renal artery duplex US, 94 % and 93 % for CTA, and 90 %
and 94.1 % for MRA, respectively. Willmann et al. [ 27 ]
obtained excellent-quality CT angiograms (92 % sensitivity
and 99 % specifi city) for the detection of hemodynamically
signifi cant arterial stenosis of aortoiliac and renal arteries. In
this study, they used a half-second MDCT scanner and a
nominal section thickness of 1 mm. Compared to MRA, there
is no statistically signifi cant difference between 3D MRA and
CTA in the detection of hemodynamically signifi cant arterial
stenosis of the aortoiliac and renal arteries. This study also
demonstrated that patient acceptance of the CT study is
higher than that of either invasive angiography or MRA.
Methods of Renal CTA
As a rule of thumb, the injection duration should match the
acquisition time in routine clinical practice. Biphasic
injection protocols with an initially high injection rate
followed by a slower continuing injection phase ensure
optimal opacifi cation of the renal arteries (Chap. 2 ). Note
that high-concentration contrast material requires only
moderate injection fl ow rates (with a maximum of 4.5 mL/s)
to achieve high iodine administration rates [ 28 ].
Image Post-processing Techniques
While most vascular beds have demonstrated an advantage of
MIP imaging over VR for accurate stenosis detection (especially coronary artery imaging), renal vasculature seems more
amenable to quantitation with VR. One study specifi cally
compared overall image quality and vascular delineation in
MIP and VR images. The authors found that all main and
accessory renal arteries depicted in invasive angiography
were also demonstrated in MIP and VR images [ 29 ]. VR per-
formed slightly better than MIP for quantifi cation of stenoses
>50 % (VR: r 2 = 0.84, p < 0.001; MIP: r 2 = 0.38, p = 0.001) and
signifi cantly better for severe stenoses (VR: r 2 = 0.83,
p < 0.001; MIP: r 2 = 0.21, p = 0.1). For detection of stenosis,
VR yielded a substantial improvement in positive predictive
value (for stenoses >50 and 70 %, VR: 95 and 90 %; MIP: 86
and 68 %, respectively). The image quality obtained with VR
was not signifi cantly better than that with MIP, but vascular
delineation in VR images was signifi cantly better (Fig. 18.11 ).
The VR technique of renal MRA enabled more accurate
detection and quantifi cation of renal artery stenosis than MIP,
with signifi cantly improved vascular delineation.
Tepe et al. [ 30 ] used 3D EBT angiography to evaluate
renal artery lesions as well as vascular variants that are
crucial to detect before surgery. Forty patients underwent
EBT (GE-Imatron, C 150 ultrafast CT scanner, San
Francisco, CA) of the renal arteries. The study demonstrated
that both MIP and VR images were excellent in demonstrating
stenosis of the renal arteries. Accessory and main renal
arteries were easily depicted, and stenosis was shown with
high accuracy. Among 40 renal angiography patients, 21 had
stenosis of the renal arteries with different percentages. A
total of 12 accessory renal arteries (fi ve left, seven right)
were detected. With its noninvasive VR and MIP techniques,
CT is easy to apply and is functional and accurate for neoplasms, renal vascular anatomy, and renal artery stenosis.
Another study evaluated fi ndings in 50 main and 11
accessory renal arteries [ 31 ]. All arteries depicted in
conventional angiograms were visualized in MIP and VR
images. Receiver operating characteristic (ROC) analysis for
MIP and VR images demonstrated excellent discrimination
for the diagnosis of stenosis of at least 50 % (area under the
ROC curve, 0.96–0.99). Sensitivity was not signifi cantly
different for VR and MIP (89 % vs. 94 %, p > 0.1), and
specifi city was greater with VR (99 % vs. 87 %, p = 0.008–
0.08). Stenosis of at least 50 % was overestimated with CTA
in four accessory renal arteries, but three accessory renal
arteries that were not depicted in conventional angiography
were depicted in CTA. In the evaluation of renal artery
stenosis, CTA with VR is faster and more accurate than CTA
with MIP. Accessory arteries that were not depicted with
conventional angiography were depicted with both CT angiographic algorithms.
Conclusion
CTA is a highly reliable technique for the detection of renal
artery stenosis and for morphologic assessment. CTA can surpass conventional angiography in terms of diagnostic accuracy and reduced exposure to iodinated contrast (Fig. 18.11 ).
In patients with renal insuffi ciency, color-coded duplex US or
gadolinium-enhanced MRA should remain as the initial
examination performed, depending on local expertise and
availability. However, new warnings regarding systemic
fi brosis with gadolinium make this agent contraindicated in
patients with glomerular fi ltration rates of <30 mg/mL/mm 2 .
Mesenteric CT Angiography
CTA has become a valuable minimally invasive tool for the
visualization of normal vascular anatomy and its variants, as
well as for pathologic conditions affecting the mesenteric
vessels (Figs. 18.12 and 18.13 ) [ 32 , 33 ]. CTA is considered
A. Alani and M.J. Budoff
https://t.me/medicina_free
329
the fi rst-line imaging test in the diagnosis of mesenteric ischemia [ 34 ]. Indications for CTA include not only acute and
chronic ischemia, aneurysm, and dissection, but also preoperative vascular assessment for patients undergoing liver
lesion embolization and in the setting of liver transplantation
[ 35 , 36 ]. In addition, mesenteric CTA can assist in the evalu-
ation of abdominal pain by ruling out other intra-abdominal
pathology.
CTA Accuracy in Diagnosis of Mesenteric
Ischemia
According to a recent review and meta-analysis that included
eight studies, CTA has a high diagnostic accuracy in the diagnosis of mesenteric ischemia. Sensitivity ranged from 83 to
100 % with a pooled sensitivity of 94 %, and specifi city ranged
from 67 to 100 % with a pooled specifi city of 95 % [ 37 ].
Methods and Image Post-processing
Techniques
Protocols for typical aortic imaging (described previously)
are used to image the mesenteric vasculature. Mesenteric
CTA has been facilitated by rapid image acquisition with
64-slice scanners, which reduce artifacts from respiratory
variation. This allows for the visualization of lesions at the
mesenteric orifi ce and evaluation of distal reconstitution.
Multiple axial images and rotational views may be necessary
to evaluate mesenteric lesions at the aortic orifi ce. The
reconstructed images allow for easy evaluation of all
abdominal vasculature. VR is most often used, predominantly
due to complex anatomy that makes MIP imaging more
diffi cult (Fig. 18.13 ). Since the arteries are highly tortuous,
leaving the 2D plane often (and traveling both caudally and
Fig. 18.11 A volume-rendered electron beam tomography (EBT)
study of the renal arteries, depicting a high-grade stenosis of the left
renal artery ( arrow ). The left kidney also opacifi es less ( darker color )
than the right kidney, suggesting decreased blood fl ow and signifi cance
of the visualized stenosis
Fig. 18.12 Maximal intensity projection of the abdominal aorta, demonstrating severe calcifi cations at the iliac bifurcation ( arrow, left image ).
The right image demonstrates a normal arterial bed in another patient, displayed using volume rendering (VR)
18 Aortic, Renal, Mesenteric and Carotid CT Angiography
https://t.me/medicina_free
330
cranially at different times), these vessels pose the most challenge with axial interpretations. With coronary imaging, the
arteries run cranial to caudal, without signifi cant exception.
Thus, interpreting with MIP or axial imaging is fairly
straightforward, as the operator needs to systematically start
from the most cranial images to the most caudal to follow the
respective arteries. With mesenteric imaging, the arteries
commonly turn both cranially and caudally, and VR enables
visualization of the entire dataset with one reconstruction.
No studies of the diagnostic potential of the different reconstruction methods have been reported.
Comparison to Other Modalities
Invasive angiography allows for diagnosis and treatment in a
single test and is thus considered the reference standard test
to evaluate acute and chronic mesenteric ischemia [ 38 ]. CTA
and contrast-enhanced MRA are excellent noninvasive
screening techniques for patients suspected of having
mesenteric ischemia from all causes. CTA has higher spatial
resolution and faster acquisition times, allowing assessment
of the peripheral visceral branches and the inferior mesenteric
artery with greater accuracy than contrast-enhanced MRA. In
addition, it allows for the identifi cation of calcifi ed plaques.
Contrast-enhanced MRA has a longer examination time that
may result in delay therapeutic intervention. In addition, it
has limited use in the diagnosis of distal stenosis and
nonocclusive mesenteric ischemia [ 39 ]. MRA is therefore
the clear second choice in this clinical setting, but the lack of
radiation and iodinated contrast agents make it the best technique for children and patients with azotemia [ 40 ].
Carotid Artery CT Angiography
Ischemic cerebrovascular events are often due to atherosclerotic narrowing of the carotid bifurcation (Fig. 18.14 ) [ 41 ].
Carotid disease contributes to stroke, transient ischemic
attacks, amaurosis fi gax through sudden occlusion, and cerebral or ocular embolization. Invasive angiography is the current reference standard for the evaluation of obstructive
carotid artery disease. CTA is a robust technique in assessing
carotid artery stenosis, allowing for excellent visualization of
the lumen of the carotid artery using intravenous contrast
(Fig. 18.15 ). Subsequent refi nement of US, CT, and MRI
techniques has led to changes in clinical practice, such that
many centers have now abandoned conventional angiography
in favor of safer imaging modalities [ 42 ].
CTA offers details of the entire relevant neurovascular axis
by excluding signifi cant carotid disease and intracranial disease [ 43 ]. Coupling non-contrast-enhanced cranial CT imag-
ing with CT perfusion imaging and CTA of the entire
cerebrovascular axis is both safe and feasible [ 44 ]. The even-
tual ability to preemptively identify asymptomatic plaques
with high likelihood to produce symptoms is the most practical goal of the CTA imaging technique, which would allow
for appropriate intervention prior to a disabling or fatal neurologic event. CTA and gadolinium-enhanced MRA have
both proved to be reliable and fast techniques to evaluate the
degree of internal carotid artery (ICA) stenosis [ 45 ]. Apart
from a hemodynamically signifi cant luminal stenosis, complexities in extracranial carotid artery plaque morphology
have also been shown to increase the risk of thromboembolic
events, including surface irregularities/ulcerations due to
plaque rupture, calcifi cation, fi brous cap thinning, intraplaque
hemorrhage, and the presence of necrotic core. Out of all the
modalities, luminal surface irregularities and ulcerations are
most frequently seen in CTA.
The North American Symptomatic Carotid
Endarterectomy Trial and European Carotid Surgery Trial
demonstrated a large reduction in strokes by performing
carotid endarterectomy [ 46 , 47 ] in symptomatic patients
with a stenosis of more than 70 %. Thus, an accurate
assessment of carotid disease is important. Furthermore,
endarterectomy in patients with a symptomatic moderate
carotid stenosis of 50–69 % produced a moderate reduction
in the risk of stroke [ 33 ]. Current practice is to use CTA to
facilitate patient triage and provide specifi c information to
rule out large vessel stenosis in patients with transient
ischemic attacks, suspected stroke, or carotid bruits
(Fig. 18.16 ) [ 42 ]. Common indications include evaluation of
patients with carotid bruits, symptoms of vertebral insuffi ciency, borderline carotid US examinations, or insuffi cient
Fig. 18.13 3D image demonstrating the ability of CT to visualize
the abdominal arteries, including the gastric arteries in this case
A. Alani and M.J. Budoff
https://t.me/medicina_free
331
Fig. 18.14 Two patients with carotid stenosis at the bifurcation. The
left image is a volume- rendered image, with a high-grade stenosis at
the proximal portion of the internal carotid, with a dense calcifi cation
also seen ( arrow ). The right image demonstrates a maximal intensity
projection image of the same region, with a tight stenosis and thrombus
present ( arrow )
Fig. 18.15 3D images of normal carotid arteries bilaterally
18 Aortic, Renal, Mesenteric and Carotid CT Angiography
https://t.me/medicina_free
332
MRA examinations of the carotid system. Many vascular
surgeons will not operate based upon carotid US, requiring
confi rmation with either CTA or invasive angiography.
Given that a large proportion of patients with carotid
artery disease will be evaluated for potential carotid artery
stenting, CT imaging should focus on assessment of the
Fig. 18.16 ( a1 ) Right external carotid artery stenosis. ( a2 ) Volume
rendered image of right external carotid artery stenosis. ( b1 ) Coronal
view of right internal carotid artery (ICA) stent. ( b2 ) Volume rendered
image of right ICA stent. ( c1 ) Axial view of left carotid artery dissec-
tion. ( c2 ) Coronal view of left carotid artery dissection. ( c3 ) Volume
rendered image of left carotid artery dissection
a1
a2
b1
b2
c1 c2 c3
A. Alani and M.J. Budoff
https://t.me/medicina_free
333
following: (1) stenosis severity, (2) disease within the aortic arch and at the origin of the common carotid arteries, (3)
the size of the common carotid artery at the lesion location,
(4) the size of the distal ICA, and (5) the presence of contralateral disease.
CTA Accuracy in Diagnosis of Carotid Artery
Stenosis
According to previous research and reviews that included old
CT scanners, contrast-enhanced MRA is more accurate than
MDCT in diagnosing carotid artery stenosis [ 48 , 49 ].
However, MDCT is quickly developing, and more highquality images are being produced. A recent prospective
study by Anzidei et al. evaluated 170 patients with suspected
carotid artery disease. They compared the diagnostic accuracy of US Doppler, steady-state contrast-enhanced MRA,
and CTA with invasive angiography as the reference standard. CTA has slightly better accuracy, sensitivity, and specifi city than MRA (97 %, 95 %, and 98 % vs. 95 %, 93 %, and
97 %, respectively). CTA has a greater accuracy than US
(97 % vs. 76 %). Moreover, CTA and MRA have an identical
ability in plaque morphology and composition analysis with
no statistical difference between the two tests [ 50 ].
Methods for Carotid CTA
Carotid CT angiographic images are obtained with patients
placed in the supine position with the head tilted back as far
as possible to avoid inclusion of dental hardware. Spiral data
can be acquired with a slice thickness of 0.5–0.625 mm starting at the seventh cervical vertebra and proceeding as far
cephalad as required. Transverse source images are reconstructed in 1-mm increments using a small fi eld of view
(15 cm). These parameters allowed for a spatial resolution of
0.3 × 0.3 × 0.6 mm. Total coverage was approximately 18 cm.
In general, good image quality is essential. A CT angiographic image of good quality is easily obtained if the patient
does not move during the study. Given the faster scan times
with increased detector systems, this is even easier. A breathhold acquisition is not necessary. Compared with invasive
angiography and CTA, a major limitation of gadoliniumenhanced MRA is spatial resolution.
With a power injector, 30–40 mL of nonionic contrast
medium is injected at a rate of 2.5 mL/s into an antecubital
vein. Administration of each bolus was followed immediately by a 20-mL saline fl ush. The acquisition is initiated
after the start of the administration of contrast medium, the
time of which was determined by a test of circulation time.
By using automatic triggering with detection of the contrast
material bolus, it is straightforward to selectively obtain an
arterial phase image. Previous studies [ 51 ] have shown that a
combination of optimal tracking volume placement and
adjustment of tracking volume size ensures optimal sensitivity to the contrast material bolus. By choosing a 20-mm
tracker volume placed in the aortic arch, bolus arrival was
always detected. Careful timing is very important, with arterial enhancement being critical. It is vital to make sure that
there is no venous fi lling when images are obtained.
Obtaining images too early will lead to non-enhanced
images, and obtaining images late allows for venous enhancement. Large jugular veins fi lled with contrast in close proximity to the carotid arteries can make the interpretation of
carotid arteries more diffi cult.
Image Post-processing Techniques
Precision in the length and degree of stenosis has been
reported to depend more on measurement technique than on
acquisition parameters [ 52 ]. The accuracy of stenosis mea-
surement depends on the scanning plane, which ideally
should be perpendicular to the carotid artery used to obtain
magnifi ed transverse oblique images. Most authors consider
MIP or curved multiplanar reconstructions as the most accurate techniques for measurements. VR is considered the least
accurate technique for measurement. CTA allows data to be
reconstructed into 2D and 3D images with cross- sectional
views that can accurately depict plaque morphology. The
images are analyzed with axial images and MIP or curved
multiplanar reconstruction. Total post-processing is now
done in real time (<1 min). MIP techniques allow data to be
reconstructed into images that closely resemble conventional
catheter-based angiograms that can be rotated 360° to be
viewed from any angle. This helps to delineate the unstable
plaques that are less stenotic but at high risk of producing
symptomatic embolization or carotid occlusion.
Plaque Composition
Plaques that are more prone to disruption fracture or fi ssuring may be associated with a higher risk of embolization,
occlusion, and consequent ischemic neurologic events [ 53 ].
The degree of arterial stenosis is the main determinant of
stroke risk in carotid artery disease, and it has been used to
select patients who will benefi t from surgical intervention
[ 54 ]. However, with recent advances in MRI and CTA imag-
ing, there has been interest in atherosclerotic plaque features
(vulnerable plaque) beyond the degree of stenosis in risk
stratifi cation for stroke. Wintermark el al. [ 55 ] found a good
correlation between the plaque composition evaluated by
CTA and histopathological fi ndings.
A recent study by Gupta et al. [ 56 ] evaluated patients with
high-grade ICA disease. There was a strong relation between
increasing soft plaque thickness measurements and ipsilateral
18 Aortic, Renal, Mesenteric and Carotid CT Angiography
https://t.me/medicina_free
334
ischemic stroke (each 1-mm increase in plaque thickness
corresponded to 2.7 times more likelihood of ipsilateral
ischemic events). A cutoff thickness of 3.5 mm of the soft
plaque can differentiate between asymptomatic and
symptomatic individuals. In contrast, calcifi ed plaque was
associated with a lower risk of disease, with maximum
thickness substantially higher in asymptomatic patients.
Acute carotid ischemic events were associated certain plaque
morphology found by CT imaging. Increased wall volume, a
thinner fi brous cap, a greater number of lipid clusters, and
lipid clusters closer to the lumen were associated with
increased risk of stroke [ 57 ].
Comparison to Other Modalities
Invasive angiography has long been considered the standard
for evaluation of carotid stenosis, but it has well-known risks
and limitations. Invasive angiography allows only a limited
number of views, which can lead to an underestimation of
the degree of stenosis by as much as 40 % [ 58 ] compared
with histological correlation. Invasive angiography is also a
relatively expensive technique that uses numerous resources.
Most importantly, there is a small but defi nite risk of major
complications secondary to the procedure itself. The
Asymptomatic Carotid Atherosclerosis Study Committee
reported a 1.2 % risk of persisting neurologic defi cit or death
following invasive angiography, while the surgical risk was
1.5 %. The risks associated with CTA are markedly lower
with similar or lower radiation exposures and no catheterinduced risks.
Carotid artery CTA has substantial benefi ts, including its
accuracy, lack of invasiveness [ 59 ], and improved spatial and
temporal resolution compared with MRA. Gadoliniumenhanced MRA is an appropriate technique for evaluating
ICA stenosis [ 60 – 62 ]. Clinically relevant stenosis and occlu-
sions of the ICA were correctly detected with good sensitivity, specifi city, and interobserver agreement. Most studies
with gadolinium-enhanced MRA demonstrate overestimation
of the degree of stenosis [ 53 , 61 , 62 ]. Artifacts due to the
excessive section thickness necessary with current MR systems cause a partial volume effect [ 58 , 63 ]. The signal loss
can also be explained by the presence of hemodynamic modifi cations. The decreased fl ow caused by stenosis leads to a
reduced concentration of contrast agent in the distal arterial
lumen, which may also explain why overestimation of stenosis with gadolinium-enhanced MRA can occur [ 64 ], espe-
cially for evaluating the degree of stenosis in small-vessel
lumens. MRA can replace invasive angiography in most
patients. However, it has been proved that CTA is highly
accurate and can replace invasive angiography [ 44 , 64 ].
In contrast to the other two modalities, CTA allows direct
visualization of the arterial wall and atheromatous plaque,
making the measurement of stenosis much easier. Almost all
authors consider that calcifi ed plaque is a limitation of
CTA. This can be minimized by using multiplanar volume
reconstruction to visualize the entire bifurcation initially
with a large-volume reconstruction. By reducing volume
reconstruction, we can clearly visualize the residual lumen at
the maximal part of stenosis, even when circumferential
calcifi ed plaques are present. Moreover, CTA is able to
differentiate mural calcifi cations and contrast material,
because the attenuations of intraluminal contrast and
calcifi cations are not similar. Therefore, calcifi cations should
not be considered limitations of CTA [ 64 ]. In addition,
carotid arteries tend to calcify less than either coronary or
peripheral arteries (perhaps because carotid arteries are more
elastic and less muscular), so dense circumferential
calcifi cations occur less frequently in this vascular bed.
Detection of ulcerated plaques may prove to be important,
since it has been suggested that the presence of plaque
ulceration is a risk factor for embolism [ 65 ]. Most studies
suggest that CTA is the best modality for analyzing plaque
morphology. Plaque irregularities are more frequent in CTA
than in invasive angiography or contrast-enhanced
MRA. However, the inability of invasive angiography to
depict plaque ulceration is well documented [ 65 , 66 ], partly
because of the limited number of views typically obtained.
The case of CTA depicting an ulceration that is not depicted
in gadolinium-enhanced MRA could be due to a lack of
spatial resolution in gadolinium-enhanced MRA.
Conclusion
Carotid CTA has matured and can be used to quantify
stenoses more precisely than US, to detect tandem stenoses,
and for the workup of acute stroke patients. The newer
scanners and multiple dose-saving strategies have the
additional advantage of a very low radiation profi le, allowing
for minimal risk to the patient and maximum visualization of
the arteries in question.
Vertebral Artery CT Angiography
Although conventional intra-arterial angiography remains
the gold standard method for imaging the vertebral artery,
noninvasive modalities such as MDCT, MRA, and US are
constantly improving and are playing an increasingly
important role in diagnosing vertebral artery pathology in
clinical practice. Normal anatomy, normal variants, and a
number of pathologic entities such as vertebral
atherosclerosis, arterial dissection, arteriovenous fi stula,
subclavian steal syndrome, and vertebrobasilar dolichoectasia
can be seen.
A. Alani and M.J. Budoff
https://t.me/medicina_free
335
Chapter Summary
During the past decade, we have been witness to a tremendous development in the fi eld of CT imaging. CTA has
gained remarkably by improvements in scan time and image
quality, replacing diagnostic angiography in many cases of
aorta, renal, mesenteric, and carotid angiography. In addition, there has been an exciting advance in techniques for
reducing radiation dose that have achieved dramatic results
and decreased radiation concerns. These vascular beds suffer
from fewer motion artifacts (except for the ascending aorta),
so imaging with CTA is ideal. CTA is less expensive and less
invasive, and it allows for simultaneous visualization of large
anatomic areas from multiple angles using 3D display.
References
1. Stanford W, Rooholamini SA, Galvin JR. Ultrafast computed
tomography in the diagnosis of aortic aneurysms and dissections.
J Thorac Imaging. 1990;5(4):32–9.
2. Katz DS, Hon M. CT angiography of the lower extremities and aortoiliac system with a multi-detector row helical CT scanner: promise
of new opportunities fulfi lled. Radiology. 2001;221(1):7–10.
3. Kim JK, et al. Living donor kidneys: usefulness of multi-detector
row CT for comprehensive evaluation. Radiology.
2003;229(3):869–76.
4. Kalender WA, Quick HH. Recent advances in medical physics. Eur
Radiol. 2011;21(3):501–4.
5. Roos JE, et al. Thoracic aorta: motion artifact reduction with retrospective and prospective electrocardiography-assisted multidetector row CT. Radiology. 2002;222(1):271–7.
6. Qanadli SD, et al. Motion artifacts of the aorta simulating aortic
dissection on spiral CT. J Comput Assist Tomogr. 1999;23(1):1–6.
7. Gotway MB, Dawn SK. Thoracic aorta imaging with multisclice
CT. Radiol Clin North Am. 2003;41(3):521–43.
8. Blanke P, et al. Thoracic aorta: prospective electrocardiographically
triggered CT angiography with dual-source CT--feasibility, image
quality, and dose reduction. Radiology. 2010;255(1):207–17.
9. Raff GL. Radiation dose from coronary CT angiography: fi ve years
of progress. J Cardiovasc Comput Tomogr. 2010;4(6):365–74.
10. Fishman JE. Imaging of blunt aortic and great vessel trauma.
J Thorac Imaging. 2000;15(2):97–103.
11. Kouchoukos NT, Dougenis D. Surgery of the thoracic aorta. N Engl
J Med. 1997;336(26):1876–88.
12. Rubin GD. Helical CT angiography of the thoracic aorta. J Thorac
Imaging. 1997;12(2):128–49.
13. Rubin GD, et al. Aorta and iliac arteries: single versus multiple
detector-row helical CT angiography. Radiology.
2000;215(3):670–6.
14. Galla JD, et al. Identifi cation of risk factors in patients undergoing
thoracoabdominal aneurysm repair. J Card Surg. 1997;12(2
Suppl):292–9.
15. Semba CP, et al. Acute rupture of the descending thoracic aorta:
repair with use of endovascular stent-grafts. J Vasc Interv Radiol.
1997;8(3):337–42.
16. Zinck SE, Primack SL. Radiographic and CT fi ndings in blunt chest
trauma. J Thorac Imaging. 2000;15(2):87–96.
17. Lu B, et al. Electron beam tomography with three-dimensional
reconstruction in the diagnosis of aortic diseases. J Cardiovasc Surg
(Torino). 2000;41(5):659–68.
18. Hobo R, Buth J, EUROSTAR Collaborators. Secondary interventions following endovascular abdominal aortic aneurysm repair
using current endografts. A EUROSTAR report. J Vasc Surg.
2006;43(5):896–902.
19. Halpern EJ. Triple-rule-out CT angiography for evaluation of acute
chest pain and possible acute coronary syndrome. Radiology.
2009;252(2):332–45.
20. Hayter RG, et al. Suspected aortic dissection and other aortic disorders: multi-detector row CT in 373 cases in the emergency setting.
Radiology. 2006;238(3):841–52.
21. Stueckle CA, et al. Multislice computed tomography angiography
of the abdominal arteries: comparison between computed
tomography angiography and digital subtraction angiography
fi ndings in 52 cases. Australas Radiol. 2004;48(2):142–7.
22. Yoshida S, et al. Thoracic involvement of type A aortic dissection
and intramural hematoma: diagnostic accuracy – comparison of
emergency helical CT and surgical fi ndings. Radiology.
2003;228(2):430–5.
23. Glockner JF, Vrtiska TJ. Renal MR and CT angiography: current
concepts. Abdom Imaging. 2007;32(3):407–20.
24. Kim D, et al. Renal artery imaging: a prospective comparison of
intra-arterial digital subtraction angiography with conventional
angiography. Angiology. 1991;42(5):345–57.
25. Sarkodieh JE, Walden SH, Low D. Imaging and management of
atherosclerotic renal artery stenosis. Clin Radiol. 2013;68(6):
627–35.
26. Rountas C, et al. Imaging modalities for renal artery stenosis in
suspected renovascular hypertension: prospective intraindividual
comparison of color Doppler US, CT angiography, GD-enhanced
MR angiography, and digital substraction angiography. Ren Fail.
2007;29(3):295–302.
27. Willmann JK, et al. Aortoiliac and renal arteries: prospective intraindividual comparison of contrast-enhanced three-dimensional MR
angiography and multi-detector row CT angiography. Radiology.
2003;226(3):798–811.
28. Fleischmann D. Multiple detector-row CT angiography of the renal
and mesenteric vessels. Eur J Radiol. 2003;45 Suppl 1:S79–87.
29. Mallouhi A, et al. 3D MR angiography of renal arteries: comparison of volume rendering and maximum intensity projection algorithms. Radiology. 2002;223(2):509–16.
30. Tepe SM, Memisoglu E, Kural AR. Three-dimensional noninvasive
contrast-enhanced electron beam tomography angiography of the
kidneys: adjunctive use in medical and surgical management. Clin
Imaging. 2004;28(1):52–8.
31. Johnson PT, et al. Renal artery stenosis: CT angiography – comparison of real-time volume-rendering and maximum intensity projection algorithms. Radiology. 1999;211(2):337–43.
32. Laghi A, et al. Multislice spiral computed tomography angiography
of mesenteric arteries. Lancet. 2001;358(9282):638–9.
33. Lawler LP, Fishman EK. Celiomesenteric anomaly demonstration
by multidetector CT and volume rendering. J Comput Assist
Tomogr. 2001;25(5):802–4.
34. Oliva IB, et al. ACR Appropriateness Criteria (R) imaging of mesenteric ischemia. Abdom Imaging. 2013;38(4):714–9.
35. Erbay N, et al. Living donor liver transplantation in adults: vascular
variants important in surgical planning for donors and recipients.
AJR Am J Roentgenol. 2003;181(1):109–14.
36. Byun JH, et al. Evaluation of the hepatic artery in potential donors
for living donor liver transplantation by computed tomography
angiography using multidetector-row computed tomography:
comparison of volume rendering and maximum intensity projection
techniques. J Comput Assist Tomogr. 2003;27(2):125–31.
37. Cudnik MT, et al. The diagnosis of acute mesenteric ischemia: a
systematic review and meta-analysis. Acad Emerg Med.
2013;20(11):1087–100.
18 Aortic, Renal, Mesenteric and Carotid CT Angiography
https://t.me/medicina_free
Соседние файлы в папке Библиотека им академика М.И. Перельмана