| Abstract |
PERIPHERAL ARTERIAL IN-STENT RESTENOSIS:
COMPARATIVE EVALUATION OF COLOR DOPPLER
ULTRASONOGRAPHY, MULTIDETECTOR COMPUTED
TOMOGRAPHY AND DIGITAL SUBTRACTION ANGIOGRAPHY
Stent – assisted angioplasty procedures are currently regarded as
primary catheter-based therapy for peripheral arterial obstructive disease.
Stenting manages to obliterate stenosis and restore arterial supply to the
periphery more efficiently compared to balloon angioplasty by inhibiting both
elastic recoil and vascular remodeling.
Primary patency rates are noteworthy, reaching 85% in the aorta and
the iliac arteries, 89% in the renal arteries and approximately 80% in the
carotid territory. Although stenting has proven effective, in-stent restenosis
may occur and lead to disease relapse.&In-stent restenosis has developed into
a significant clinical problem and if left untreated, the deprivation of arterial
flow can cause severe ischemia to organs and tissues.
Late intrastent lumen loss is the result of intimal hyperplasia. The
cellular basis of in-stent restenosis has been clarified as the unavoidable
inflammatory response triggered by the mechanical trauma caused by the
deployment of stent. The endothelial lining gets disrupted and the propagated
injury to the media and adventitia result in smooth muscle cell and
myofibroblast migration and proliferation of them within the intima. After
several weeks cellularity decreases and collagen-based matrix occupies the
hyperplastic lining. The peak tissue accumulation occurs within the first six
months after stent implantation. The hyperplasia evolves to fibrotic tissue
between 6 months and 3 years and stabilizes or minor declines onwards.
Currently there is no consensus on the best management approach of
patients with stent-assisted peripheral revascularization, regarding either the
precise timing or the proper screening method.& The reference standard for
identifying and assessing in-stent restenosis is transcatheter angiography, an
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invasive procedure whitch is associated with several complications. It is
questionable whether an invasive method should be used as a follow-up tool
and there appears the necessity for its replacement by non-invasive methods
that are accurate enough to distinguish significant hyperplasia that would
justify (in this case therapeutic) intervention. The current alternatives include
color Doppler ultrasonography, Magnetic Resonance Imaging and Computed
Tomography, all of them suffering from certain limitations.
Current literature considers modern multidetector computed
tomography as the most attractive non-interventional alternative for the
assessment of in-stent restenosis. Modern multidetector computed
tomography systems provide significant spatial and temporal resolution that
enable direct visualization of hyperplasia and quantification of restenosis with
high sensitivity rates and almost absolute negative predictive value.
Multidetector Computed Tomography imaging is considered to be a high-dose
diagnostic procedure and the potential mitogenic effect of ionizing radiation
raises great concern about its use as a follow-up tool. Recent reported
experience in low dose computed tomography angiography has shown that
low radiation exposure settings in MDCT angiography could serve as a safe
and clinically acceptable imaging protocol. To the present there has been no
published experience regarding the value of low dose MDCT protocols in the
evaluation of the peripheral arterial stents and the assessment of in-stent
restenosis.
The purpose of the current study was to explore the efficacy of reduced
exposure multidetector computed tomography protocols in the quantitative
assessment of in-stent restenosis of the peripheral arterial stents and to
compare the results with these from digital subtraction angiography and color
Doppler ultrasonography. We suggested and followed a dual research
prospective scheme of both in-vitro and in-vivo study, with laboratory
simulation data being applied to volunteer patient groups with various stented
arterial segments (in the renal, iliac, superior mesenteric, femoral and
popliteal arteries) and correlated the results to catheter angiographic and
color Doppler ultrasonographic data. The Computed Tomography system
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used for both the in-vitro and the in-vivo study was a modern 16-row detector
unit (Siemens Somatom Sensation, Siemens AG, Forchheim, Germany).
A. In-vitro study
We used a Rando anthropomorphic phantom (Alderson Research
Labs, Stanford, CA) to simulate a patient with in-stent restenosis in the
external iliac and proximal femoral artery. We used a modern “shape memory”
nitinol stent 10mm in diameter. Custom-made wax was carefully fabricated to
simulate concentric hyperplastic tissue and the cylindrical free lumen was
filled with a solution of iodine contrast medium diluted in saline, representing
patient’s blood during computed tomography angiography. We simulated
clinical relevant in-stent stenosis of 39%, 49% and 59%.& The phantom was
subjected to standard- and low-dose angiographic exposures using the 16-
row multidetector CT scanner. The percentage of measured restenosis was
determined using the profile along a line normal to the lumen axis on
reconstructed images of 2 and 5 mm slice thickness. Percentage in-stent
restenoses derived using the standard- and low-dose protocols were
compared. Using the Monte Carlo method we estimated the effective dose for
individuals for the various scans.
We managed to image and quantify the simulated hyperplastic tissue in
all of the low exposure protocols. The accuracy in measuring the percentage
restenosis was found to be better than 12% for all simulated stenoses (10%,
12% and 12% for the 39%, 49% and 59% stenosis respectively). The
differences between percentage restenosis measured on images obtained at
120 kVp/160 mAs and 80 kVp/80 mAs were below 6%. Effective dose
reduction was quite significant and the estimated percentage reduction
reached almost 85% at 80 kVp/ 80 mAs settings compared to standard 120
kVp/ 160 mAs protocol.
We conclude that the exposure factors during Multidetector Computed
Tomography angiography for the evaluation of a stented iliac or proximal
superficial femoral artery may be significantly reduced without affecting the
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accuracy in determining the degree of in-stent restenosis, with a difference of
΄&λτ6% even at the lowest exposure of 80kVp / 80mAs we tested. There seems
to be a high potential for reducing the patient radiation burden from computed
tomography angiography for the evaluation of in-stent restenosis to
significantly less than that associated with intraarterial subtraction
angiography.
Our results have already been published in the British Journal of
Radiology as follows:
• K. Perisinakis, E. Manousaki, K. Zourari, D. Tsetis, A. Tzedakis, A.
Papadakis, A. Karantanas, J. Damilakis. Accuracy of multislice CT
angiography for the assessment of in-stent restenoses in the iliac
arteries at reduced dose: a phantom study. Br J Radiol.
2011;84(999):244-50
B. In-vivo study
We prospectively explored the efficacy of low dose computed
tomography angiography protocols in our 16-row scanner to assess renal,
iliac, superior mesenteric, femoral and popliteal in-stent restenosis. Patients in
regular follow-up protocols enrolled under informed consent. The results from
the low exposure computed tomography scans were compared to that of
standard exposure protocols as well as to the findings of color Doppler and
intraarterial subtraction angiography.
Sixteen patients with 19 renal arterial stents of the same material and
size, 12 patients with 15 iliac artery stents, 14 patients with femoral and
popliteal stents and one patient with superior mesenteric artery stent (studied
twice) underwent multiphasic computed tomography and color Doppler
ultrasonography. Digital subtraction angiography was also performed in the
clinical need for reintervention.
The multiphasic contrast-enhanced computed tomography angiography
protocol consisted of a true arterial phase at standard settings of 120kVp tube
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voltage for all patients. The late arterial scan was at 100kVp for 9 patients with
renal artery stents, 6 patients with iliac stents, 6 patients with femoral and
popliteal stents and for the patient with the superior mesenteric stent studied
twice. The late arterial scan was at 80kVp for 7 patients with renal artery
stents, 6 patients with iliac stents and 8 patients with femoral and popliteal
stents. Images were reconstructed under various algorithms. Assessment of
angiographic quality based on density measurements followed and the
angiographic scans were further evaluated both quantitativelly and
qualitatively in terms of vessel delineation and in-stent stenosis assessment
by two observers. Volume CT dose-index was recorded and dose reduction
between phases was calculated.
Angiographic quality maintained in 5 cases with renal artery stents, 5
cases with iliac stents and 4 cases of femoral and popliteal stents at 80kVp.&
Angiographic quality maintained in 5 cases with renal artery stents, 5 cases
with iliac stents, 5 cases of femoral and popliteal stents and for both imaging
sessions of the superior mesenteric artery stent at 100kVp.
Regarding imaging of the renal artery stents, the 120kVp protocol
performed better in all vessels and reconstruction algorithms. There proved
no significant difference between signal-to-noise ratio and contrast-to-noise
ratio at 100kVp under B31f reconstruction algorithm compared to 120kVp. All
100kVp scans were diagnostic. Tube voltage of 80kVp was associated with a
significant increase in image noise that downgraded image quality and
produced various non-diagnostic image sets. No difference in assessment of
restenosis of the renal artery stents was observed between 120kVp and the
diagnostic low exposure scans. The two 100kVp scans of the superior
mesenteric stent were also adequate for diagnosis. As far as the iliac, femoral
and popliteal stents are concerned, 100kVp protocols allowed for safe
estimation of restenosis with minor loss of image quality. Low exposure
protocols of 80kVp maintained safe diagnostic quality of in-stent restenosis
only in the femoral and popliteal territory. The findings of all cases of
diagnostic quality of the low dose computed tomography angiography were in
accordance with color Doppler ultrasonography and intraarterial subtraction
angiography results.
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Mean percentage dose reduction in the computed tomography scans of
the patients with renal artery stents was estimated 44.5% at 100kVp and
76.7% at 80kvp. Mean percentage dose reduction in the computed
tomography scans of the patients with iliac, femoral and popliteal artery stents
was estimated 47.5% at 100kVp and 79.3% at 80kvp. For the case with the
superior mesenteric artery stent the corresponding dose reduction was 44.7%
at 100kVp.
We conclude that peripheral arterial computed tomography
angiography and stent patency evaluation are feasible at 100kVp with minor
loss of image quality and almost half radiation exposure. In-stent restenosis
assessment under low exposure comes up with results comparable to
standard computed tomography protocols as well as color Doppler or
intraarterial subtraction angiography results. More conservative low exposure
protocols of 80kVp seem to apply only in the femoral and popliteal territory.
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Επαναστένωση των ενδοαγγειακών προθέσεων (stent) των περιφερικών αγγείων : συγκριτική μελέτη με έγχρωμη doppler υπερηχοτομογραφία,πολυτομική υπολογιστική τομογραφία και ψηφιακή αφαιρετική αγγειογραφία
