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Vascular and Intravascular Imaging Trends, Analysis, and Challenges, Volume 1
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the boundaries from the two techniques, the bias was further reduced to 0.074 ±
0.068 mm, which demonstrated that the two techniques could be considered as complementary.
The fourth technique, i.e. CAUDLES-EF [64], can extract the far double line (i.e.LI and MA) in the carotid artery using an edge ow technique based on directional probability maps using the attributes of intensity and texture. CAUDLES-EF was validated against manual tracings on a large dataset of 300 longitudinal B-mode carotid images with normal and pathologic arteries. In comparison to previous techniques such as CULEXsa and CALEXia, CAUDLES-EF performed the best with a high gure-of-merit (FoM) of 94.8%.
The fth technique, i.e. CAILRS [38], can automatically segment the intima layer of the far wall based on mean shift classication. CAILRS was validated against manual tracings on a large dataset of 300 longitudinal B-mode carotid images. CAILRS was benchmarked against a semi-automatic technique based on an FOAM edge operator. The proposed technique showed an IMT bias of 0.035 ± 0.186 mm. In comparison to all the previous techniques, such as CULEXsa, CALEXia, CALSFOAM and CAUDLES-EF, CAILRS showed the highest FoM of 95.6% compared to the other proposed techniques.
In 2012, Molinari et al proposed two more automated IMT measurement techniques: Completely Automated Multi-resolution Edge Snapper (CAMES) [53] and Carotid Measurement Using Dual Snakes (CMUDS) [65]. The rst technique, CAMES [53], consists of two stages. Stage one consists of automated carotid artery recognition based on a combination of scale-space and statistical classication in the multi-resolution framework, and stage two targets IMT measurement by performing an automated segmentation of LI and MA interfaces for the far (distal) wall. By carrying out a study on 365 B-mode longitudinal carotid images, the study found an
8.4% increase in the FoM compared to their previous technique CALEXia. The study concluded that CAMES was a suitable and a validated clinical tool for automating and improving cIMT measurement in multicenter large clinical trials.
The second technique, CMUDS [65], used a snake-based approach for estimating the LI and MA borders. The technique used a novel rst-order absolute moment­based external energy, which provides stable deformation. The dual snakes evolve simultaneously and are forced to maintain a regularized distance to prevent collapsing or bleeding. By carrying out a study on 665 B-mode longitudinal carotid images, the study produced a very high FoM of 98.4%. Wilcoxon and Fishers test further proved its accuracy, making this system adaptable for large multi-center studies.
In 2013, Saba et al proposed the automated IMT measurement technique CARES 3.0 [66]. CARES 3.0 is an upgrade of CARES, proposed previously by Molinari et al [63] in 2011. After automated localization of the carotid artery, the LI/MA segmentation followed four stages: stage 1 consisted of the creation of the guided zone (i.e. ROI); in stage 2, edge enhancement was performed using the FOAM operator; stage 3 performed a heuristic search for locating the LI/MA peaks; nally, in stage 4, LI/MA regularization was performed. In a study on 250 patients, the results showed 80% of the images as having an IMT measurement bias ranging
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between 50% and +50%. The results outperformed previous CARES releases and showed high accuracy and reproducibility for IMT measurement.
A few months later, the same group [43] performed intra- and inter-observer variability analysis and computed the measurement error of their recently proposed completely automated IMT measurement software AtheroEdge
TM
. The study was carried out on 200 carotid ultrasound images acquired from 50 asymptotic women patients. The intra- and inter-observer variability was tested using three readings. The measurement errors of AtheroEdgefor the automated and semi-automated methods were 0.0004 ± 0.158 mm and 0.008 ± 0.157 mm, respectively, compared to the mean value of three expert readers. The FoMs were 99.9% and 98.9% compared to the mean value of the three expert readers and 99.8% and 99.9% compared to a commercial ultrasound scanner (using the automated and semi­automated method, respectively). The intra-class CC of the three independent users was 0.98. The proposed AtheroEdgesoftware showed a diagnostic accuracy of 90%, proving its application in processing large datasets for CCA and avoiding subjectivity in cIMT measurements.
These systems were mainly research-based and did not allow for cross-institu­tional clinical trials [38, 43, 48, 53, 58, 59, 6265]. To allow for the use of cIMT measurements to occur across institutions in a reproducible fashion, improving the uniformity and reliability of cIMT is critical. Therefore, we propose the use of cloud­based technology in order to allow for cross-institutional participation. The use of information technology to support clinical services is a major driver for the push to include cloud-based solutions in healthcare. Mobile or hand-held machines, such as the iPhone and iPad, have been rapidly accepted in many countries as point-of-care solutions, providing access to healthcare data and statistics in ways that were not previously conceivable [60]. Smartphones with faster processors, improved memory and smaller batteries, in concert with highly efcient operating systems, are affecting our personal and work environments [67]. The use of these pervasive technologies in healthcare provides an anytime–anywhere solution so patients and healthcare providers can both benet from better atherosclerosis disease management.
12.6.4 A note on PoM, cross-correlation and ROC analysis
In this study, we computed the PoM for AtheroCloudand sonographer cIMT readings. The PoM computes the closeness of AtheroCloudand sonographer cIMT readings against the manual cIMT. Tables B3 and B4 clearly revealed the percentage improvement of the PoM and CC of AtheroCloudover sonographer readings, as shown in the appendix B. This proved our hypothesis that the error between the automated AtheroCloudsoftware system and manual tracings (gold standard) was lower compared to the error between the sonographer readings and manual tracings. In this study, we also analyzed the correlation between age and left and right cIMT readings computed using AtheroCloud, manually and by a sonographer. The CC is moderate and mild which showed an increase in the risk of a CAD with advancement in age. The combined cumulative distribution error curves of cIMT for (i) AtheroCloudversus manual, (ii) sonographer versus manual and
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(iii) AtheroCloudversus sonographer are shown in gure 12.11. We observed that about 23% of the patientscIMT was calculated more accurately in AtheroCloud compared to sonographer readings. The AUCs for the AtheroCloudand sonographer were 0.99 and 0.81, respectively, which further conrms the accuracy and reliability of our proposed system. Even though the automated system performs better compared to the manual readings and sonographer readings, there are subtle factors which we did not consider while designing this study. These include studying the effect of lighting conditions during the manual tracings [68], the attention of the sonographer while taking his/her readings, such as his/her mood, experience recording sonographer readings and type of image format (DICOM versus JPEG), as this can affect performance [69]. This is beyond the scope of this pilot study. We have, however, adapted a standardized software (ImgTracer, AtheroPoint, Roseville, CA, USA), which has been applied to several studies in medical imaging [7075].
12.6.5 Risk stratication
In the current analysis, we showed the risk stratication using the FRS. A risk score was derived for each patient using the gender-specic prediction formulae proposed by Wilson [57] based on the following standard conventional cardiovascular risk factors. Using the above technique, we stratied the population in low-, medium­and high-risk bins.
Table B5 clearly shows the percentage improvement of cIMT for left and right cIMTs for the cloud-based (AtheroCloud) over the desktop-based (AtheroEdge) system, as shown in appendix B. The percentage differences of AtheroCloudto AtheroEdge™ were 2.27% and 3.75% for left and right cIMTs, respectively.
12.6.6 Strengths, weaknesses and extensions
The proposed automated cloud-based system can be a very valuable tool for multi­center clinical trials and useful in the Routine mode to interface with OEM machines for cIMT computation. The proposed system is reliable, accurate, reproducible, cost-effective and fast (less than ve seconds per image). The system is fully automated and can fall back on a user-interactive solution. Our pilot design has a multi-tenancy paradigm; hence multiple centers can use it at the same time. Further, the cloud servers can be changed to elastic, and therefore it is scalable depending upon usage. It can not only accept images from various ultrasound scanners, but also in various image formats. The system automatically computes the carotid SSI and the design has an inbuilt database of patient record systems that can be shared electronically or printed. This pilot study was performed in a private cloud, but can run in available public clouds such as IBM, Amazon or Hewlett Packard (HP). Batch-processing further improves the processing speed and provides a reproducible feature needed for pharmaceutical trials and can be used as a teaching tool. Thus, the proposed system is a fully automated 24/7 system (anytime–anywhere solution) with multiple features that bring more user-friendliness compared to a sonographers
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manual methods. Even though the proposed system is fully automated and very fast, it offers certain challenges and limitations:
(a) The processing speed of AtheroClouddepends on the speed of the WIFI
or land-line connection. If the internet speed is slow, it can be challenging for the physician to load imaging and process images.
(b) The clouds cost can also increase over time, but as cloud-based technol-
ogies evolve, we expect the systems to become more economical [76] for hospital and clinic-based settings.
Finally, since our local server is Windows-based, all the encryption is performed using Microsoft bit blocker device encryption and these details are outside the scope of this pilot study. All the transfer and storage is performed by the Microsoft server. This is a pilot research study, so no cost analysis was attempted. This is being adopted as a service model and it can be used in a service setting. Current reports are produced in PDF, Word or Excel-sheet formats. It can be converted to HTML format (H7 format) for universal usage. Under the information technology frame­work, more work can be accomplished as part of future research studies, but the current results are truly encouraging.
12.7 Conclusion
We presented AtheroClouda completely automated, cloud-based, point-of-care system for ultrasound carotid intima–media thickness measurement. AtheroCloud cIMT readings were compared against sonographer readings and showed superior performance. AtheroCloud showed its usability in the Routine and Pharmaceutical modes when benchmarking against the desktop-based AtheroEdge(AtheroPoint, Roseville, CA) system, which was previously benchmarked against a Siemens system. Comprehensive statistical analyses were performed demonstrating its reliability. Although more tests need to be performed for this pilot study, current results show that the system can be adopted in the clinical setting for the clinical Routine mode or multicenter Pharmaceutical Trial mode.
Acknowledgments
Reprinted from Saba L, Banchhor S K, Suri H S, Londhe N D, Araki T, Ikeda N, Viskovic K, Shaque S, Laird J R, Gupta A, Nicolaides A and Suri J S 2016 Accurate cloud-based smart IMT measurement, its validation and stroke risk stratication in carotid ultrasound: a web-based point-of care tool for multicenter clinical trial Comput. Biol. Med. 75 217–34, with permission from Elsevier.
Funding
This research did not receive any specic grant from funding agencies in the public, commercial, or not-for-prot sectors.
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Conicts of interest
The authors declare no conict of interest.
Appendix A Polyline distance metric and precision-of-merit for
AtheroCloudcIMT measurements
This section presents a brief derivation for the computation of the PoM for AtheroCloud™ cIMT measurements. Section A.1 presents the mathematical deriva- tion for the polyline distance method (PDM) used for the measurement of AtheroCloud™ cIMT [39, 40] and section A.2 presents the derivation of the PoM [63].
A.1. Polyline distance metric
The PDM is used to measure the cIMT. It measures the changes of the contours of the far wall LI interface and MA interface. Let the rst contour LI be denoted by C and a reference point on this contour be (p0,q0). Let the second contour MA be denoted by C a line segment s. Next reference point Let the distances between the reference point (p be d
and d2. Let λ be the distance of the reference point
1
The perpendicular distance between the line segment s and the reference point given by
and the two consecutive points on C2be (p1,q1) and (p2,q2), forming
2
is obtained, which is the distance between the
v
s(, )
pq(, )
on C1and the line segment formed by the two points on C2.
00
, q0) and the two consecutive points
0
towards the line segment s.
. Using the calculus, one can derive the value of λ and⊥as follows:
1
is
−−+− −
qqqq pppp
()()( )( )
2101 2 10 1
The distance
λ =
−+−
pp qq
()()
21221
−−+−−
qqpp ppqq
()( )( )()
211 0 2 101
=
d
between the vertex
v
s(, )
−+−
pp qq
()()
21221
2
2
and the line segment s can be
.
(A.1)
(A.2)
mathematically given as
The process to obtain
and is given by
C
1
v
(, )
=
ds
dC C d C( , ) ( , ), (A.4)
⎧ ⎨ ⎩
v
dd
min{ , } 0, 1
12
d
is repeated for the rest of the points of the contour
s(, )
=
λλ
<>
⩽⩽
01
v
i12 2
=
iN1
λ
. (A.3)
where n is the number of points in the contour C1, andC2is the segment on contour C
. Second, the algorithm above is repeated where C2now becomes the reference
2
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contour and C1becomes the segment contourC1. The reverse can be represented by d(C
). Lastly, combining both d(C1,C2) and d(C2,C1) will yield the equation
2,C1
below which is the PDM:
(: )
DC C
S 12
=
dC C dC C
( vertices vertices )
#+#
+
12 21
CC
ϵϵ
12
.
(A.5)
(, ) (, )
In this study, we have used the term PDM which is a more convenient expression for equation (A.5). We will use equation (A.5) for computation of AtheroCloud cIMT and PoM in section A.2.
A.2 Precision-of-merit for AtheroCloudcIMT measurements
Given that LI
AtheroCloud
and MA
AtheroCloud
are the interfaces computed using the AtheroCloudautomated method, we compute the AtheroCloudcIMT using the PDM equation (A.5) and it is given as
AtheroCloud AtheroCloud AtheroCloud
=cIMT PDM (LI , MA ). (A.6)
Similarly, using the denition of PDM, we can compute the cIMT measurements
using manual tracings using equation (A.5), given as
=cIMT PDM (LI , MA ). (A.7)
Manual Manual Manual
Let AtheroCloudcIMTibe the cIMT value automatically computed by the proposed system, AtheroCloud, on the ith image of the database of N patients. If a database of N images is considered, then the overall mean AtheroCloudcIMT estimate can be dened as
cIMT
AtheroCloud AtheroCloud
1
=
cIMT . (A.8)
N
=
iN1
i
Correspondingly, if manual cIMTiis the cIMT value computed from the radiologists traced manual measurements, the mean manual cIMT for the manual is given as
cIMT
Manual Manual
1
=
cIMT . (A.9)
N
=
iN1
i
The overall systems performance can be computed using PoM in percentage as
AtheroCloud
=−
⎜ ⎝
cIMT
Manual
cIMT cIMT
AtheroCloud Manual
⎞ ⎟
⎤ ⎥
100 . (A.10)
*PoM (%) 100
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Appendix B Tables
Table B1. PoM for left, right and combined cIMTs.
Parameters Left cIMT Right cIMT Combined cIMT
AtheroCloudwhen compared to sonographer
AtheroCloudPoM 89.47% 86.29% 87.94%
Table B2. CC between the three methods for left, right and combined cIMTs.
Parameters Left cIMT Right cIMT Combined cIMT
Method 3: AtheroCloudand sonographer
CC 0.70 0.62 0.66
Table B3. Percentage improvement of PoM for left, right and combined cIMTs.
% Improvement of AtheroCloudover sonographer
Parameter Left cIMT Right cIMT Combined cIMT
PoM 2.98% 9.93% 6.23%
Table B4. Percentage improvement in CC for left, right and combined cIMTs.
% Improvement of AtheroCloudover sonographer
Parameter Left cIMT Right cIMT Combined cIMT
CC 29.73% 49.23% 40.58%
Table B5. Percentage difference between AtheroCloudand AtheroEdgesystems for left cIMT and right cIMT.
% Difference between AtheroCloud (cloud-based) and AtheroEdge(desktop-based)
Parameter Left cIMT Right cIMT
cIMT 2.27% 3.75%
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