Dynamic 4D-CT Angiography post-EVAR for Early Detection, Classification, and Management of Endoleaks
Date Issued
January 2024
Author(s)
Advisor
Abstract
Abdominal aortic aneurysms are defined as an abnormal, irreversible dilatation of the
abdominal aorta typically exceeding 3 cm in the greatest diameter or more than 50% of
its normal anteroposterior diameter. The primary minimal intervention treatment of
abdominal aortic aneurysms are endovascular aneurysm repairs. Endoleak is considered
the most commonly occurring complication after EVAR, thus demanding frequent post operative follow-ups.Endoleaks represent persistent perfusion into the residual aneurysm
sac, that may lead in sac expansion. Therefore, accurate diagnosis of endoleak type using
adequate imaging surveillance or re-intervention is crucial for better long-term survival
rates.
The main aim of this study is to evaluate an innovative customized dynamic CTA imaging
protocol for the early detection, classification, and management of endoleaks following
endovascular aneurysm repair of abdominal aortic aneurysms. The establishment of this
protocol improves the accuracy and confidence in detecting or excluding the presence of
endoleaks.
Triphasic conventional computed tomography angiography protocol, routinely performed
for endovascular aneurysm repair surveillance involves three static images of
unenhanced, arterial and delayed venous phase. However, the variability in contrast
arrival and washout time and the complexity of the stent graft for each patient in CT
imaging precludes accurate characterization of endoleak type and identifying target
vessels for the treatment of safe and targeted re-intervention.
In recent years, advanced dual-source dual-energy CT systems with alternating table
positions allow for dynamic acquisitions of the endograft's hemodynamics, the aneurysm
sac, and all the aortic branches with a continuous visualization of the contrast media flow,
thus detecting with accuracy the type of endoleak.
Ten patients scheduled for their routine CTA examination of the abdominal aorta post EVAR at German Oncology Center, were prospectively studied. Two patients were
excluded from the study because of the absence of endoleaks. This retrospective study
was approved by the local Bioethics committee (2023.01.166) and all participants
provided written informed consent before the examination.
vii
The patients were examined with a time-resolved CT angiographic protocol consisting of
12 low-dose phases with 60-80 mL of iodine contrast media. A dual energy acquisition
was obtained as a delayed scan having the valuable benefits of the two x-ray photon
energy spectra. Even when the venous phase was acquired too late or too early and
contrast washed out, the application of virtual monoenergetic images and iodine maps
increased the visualization of contrast enhancement. The dynamic series were assessed
with the use of syngo. CT Dynamic Angio and syngo. CT Body Perfusion application in
order to analyze them quantitatively and qualitatively and provide quantitative parameters
to maximize the accuracy of the endoleak source. The venous dual energy series were
assessed with the use of syngo. CT Dual Energy application to identify any minimal, low flow endoleaks. The dCTA revealed eight type II endoleaks and one type I endoleak.
The analysis, conducted using dynamic CT angiography, revealed a significant difference
in the mean enhancement between the aorta and endoleak. Certain endoleaks have a slow
flow, appearing between 40 to 44 seconds after contrast injection, while others manifest
as early leaks, detected between 24 to 37 seconds. The phase with the best contrast
enhancement among the 12 phases of our time-resolved CTA protocol showed a mean
attenuation value in the aortic lumen for all the patients 737.8 HU. The mean attenuation
value of the aneurysm sac (noise) was 47 HU. Mean attenuation value of the endoleak
was 555 HU. The average contrast-to-noise ratio of the aortic lumen for all the dynamic
CTA phases was 16 and the average CNR of the endoleak was 11.8. All patients did not
have a significant change in their aneurysm sac diameter except patients 6 and 10 who
had a 19.6% increment of the aneurysm diameter and 12.9% respectively. Also, the same
patients had a significant SVG with both the manual volumetric measurement method of
the aneurysm sac and the ellipsoid method.
The mean protocol radiation dose was 1134 mGy cm and the mean effective dose was
17.0 mSv. The overall average score of the quality assessment, encompassing evaluations
from all the radiologists, was reported as 4 categorizing the protocol as ‘good’.
The systematic review of the published studies designates that, the DLP of the dynamic
CTA protocol, which includes a noncontrast phase, a dynamic phase with 12 series, and
a dual-energy venous phase, is in most cases significantly lower than the conventional
CTA protocol. Additionally, the contrast media volume being given to the patients with
dynamic CTA protocols was significantly lower than the contrast media volume of the
viii
cCTA protocol due to the lowest tube kV used in the dynamic CTA protocol. This
ustocustomized dynamic CT protocol had a lower contrast dose compared to other
publications and a lower/comparable radiation dose.
The thesis concludes that 4D CTΑ with the use of quantitative analysis regarding
perfusion maps showed excellent diagnostic accuracy and demonstrated feasibility in
objective endoleak analysis and can aid the differential diagnosis of endoleak types.
This study introduces a novelty protocol that combines dynamic CTA and dual energy
for evaluating the presence of endoleaks. Furthermore, no other study or publication has
employed both the ellipsoid and volumetric methods to measure sac volume growth and
subsequently compared these values. Additionally, no other assessment of endoleak
revealed endoleak iodine concentration values extracted from the dual energy iodine
maps.
Some future perspectives for this thesis involve expanding the patient sample size to
enable a more comprehensive evaluation of the protocol across a larger population and
explore additional perfusion parameters to ascertain whether the endoleak represents a
high or low-risk leakage based on these perfusion values. Also, iodine concentrations can
provide a potential biomarker for diagnosis of a sac enlargement or a high/low flow
endoleaks.
abdominal aorta typically exceeding 3 cm in the greatest diameter or more than 50% of
its normal anteroposterior diameter. The primary minimal intervention treatment of
abdominal aortic aneurysms are endovascular aneurysm repairs. Endoleak is considered
the most commonly occurring complication after EVAR, thus demanding frequent post operative follow-ups.Endoleaks represent persistent perfusion into the residual aneurysm
sac, that may lead in sac expansion. Therefore, accurate diagnosis of endoleak type using
adequate imaging surveillance or re-intervention is crucial for better long-term survival
rates.
The main aim of this study is to evaluate an innovative customized dynamic CTA imaging
protocol for the early detection, classification, and management of endoleaks following
endovascular aneurysm repair of abdominal aortic aneurysms. The establishment of this
protocol improves the accuracy and confidence in detecting or excluding the presence of
endoleaks.
Triphasic conventional computed tomography angiography protocol, routinely performed
for endovascular aneurysm repair surveillance involves three static images of
unenhanced, arterial and delayed venous phase. However, the variability in contrast
arrival and washout time and the complexity of the stent graft for each patient in CT
imaging precludes accurate characterization of endoleak type and identifying target
vessels for the treatment of safe and targeted re-intervention.
In recent years, advanced dual-source dual-energy CT systems with alternating table
positions allow for dynamic acquisitions of the endograft's hemodynamics, the aneurysm
sac, and all the aortic branches with a continuous visualization of the contrast media flow,
thus detecting with accuracy the type of endoleak.
Ten patients scheduled for their routine CTA examination of the abdominal aorta post EVAR at German Oncology Center, were prospectively studied. Two patients were
excluded from the study because of the absence of endoleaks. This retrospective study
was approved by the local Bioethics committee (2023.01.166) and all participants
provided written informed consent before the examination.
vii
The patients were examined with a time-resolved CT angiographic protocol consisting of
12 low-dose phases with 60-80 mL of iodine contrast media. A dual energy acquisition
was obtained as a delayed scan having the valuable benefits of the two x-ray photon
energy spectra. Even when the venous phase was acquired too late or too early and
contrast washed out, the application of virtual monoenergetic images and iodine maps
increased the visualization of contrast enhancement. The dynamic series were assessed
with the use of syngo. CT Dynamic Angio and syngo. CT Body Perfusion application in
order to analyze them quantitatively and qualitatively and provide quantitative parameters
to maximize the accuracy of the endoleak source. The venous dual energy series were
assessed with the use of syngo. CT Dual Energy application to identify any minimal, low flow endoleaks. The dCTA revealed eight type II endoleaks and one type I endoleak.
The analysis, conducted using dynamic CT angiography, revealed a significant difference
in the mean enhancement between the aorta and endoleak. Certain endoleaks have a slow
flow, appearing between 40 to 44 seconds after contrast injection, while others manifest
as early leaks, detected between 24 to 37 seconds. The phase with the best contrast
enhancement among the 12 phases of our time-resolved CTA protocol showed a mean
attenuation value in the aortic lumen for all the patients 737.8 HU. The mean attenuation
value of the aneurysm sac (noise) was 47 HU. Mean attenuation value of the endoleak
was 555 HU. The average contrast-to-noise ratio of the aortic lumen for all the dynamic
CTA phases was 16 and the average CNR of the endoleak was 11.8. All patients did not
have a significant change in their aneurysm sac diameter except patients 6 and 10 who
had a 19.6% increment of the aneurysm diameter and 12.9% respectively. Also, the same
patients had a significant SVG with both the manual volumetric measurement method of
the aneurysm sac and the ellipsoid method.
The mean protocol radiation dose was 1134 mGy cm and the mean effective dose was
17.0 mSv. The overall average score of the quality assessment, encompassing evaluations
from all the radiologists, was reported as 4 categorizing the protocol as ‘good’.
The systematic review of the published studies designates that, the DLP of the dynamic
CTA protocol, which includes a noncontrast phase, a dynamic phase with 12 series, and
a dual-energy venous phase, is in most cases significantly lower than the conventional
CTA protocol. Additionally, the contrast media volume being given to the patients with
dynamic CTA protocols was significantly lower than the contrast media volume of the
viii
cCTA protocol due to the lowest tube kV used in the dynamic CTA protocol. This
ustocustomized dynamic CT protocol had a lower contrast dose compared to other
publications and a lower/comparable radiation dose.
The thesis concludes that 4D CTΑ with the use of quantitative analysis regarding
perfusion maps showed excellent diagnostic accuracy and demonstrated feasibility in
objective endoleak analysis and can aid the differential diagnosis of endoleak types.
This study introduces a novelty protocol that combines dynamic CTA and dual energy
for evaluating the presence of endoleaks. Furthermore, no other study or publication has
employed both the ellipsoid and volumetric methods to measure sac volume growth and
subsequently compared these values. Additionally, no other assessment of endoleak
revealed endoleak iodine concentration values extracted from the dual energy iodine
maps.
Some future perspectives for this thesis involve expanding the patient sample size to
enable a more comprehensive evaluation of the protocol across a larger population and
explore additional perfusion parameters to ascertain whether the endoleak represents a
high or low-risk leakage based on these perfusion values. Also, iodine concentrations can
provide a potential biomarker for diagnosis of a sac enlargement or a high/low flow
endoleaks.