If you don't remember your password, you can reset it by entering your email address and clicking the Reset Password button. You will then receive an email that contains a secure link for resetting your password
If the address matches a valid account an email will be sent to __email__ with instructions for resetting your password
Co-Registration of Peripheral Atherosclerotic Plaques Assessed by Conventional CT Angiography, MicroCT and Histology in Patients with Chronic Limb Threatening Ischaemia
CVPath Institute, Gaithersburg, MD, USAUniversity Hospital of Strasbourg, Department of Vascular Surgery and Kidney Transplantation, Strasbourg, FranceGEPROVAS, Strasbourg, France
To co-register conventional computed tomography angiography (CTA), with ex vivo micro-computed tomography (microCT) and histology of popliteal atherosclerotic plaques. Improving the non-invasive imaging capabilities may be valuable to advance patient care with peripheral arterial obstructive disease towards lesion and individual based treatment.
Methods
In this prospective observational study, 12 popliteal arteries from 11 symptomatic patients who had undergone transfemoral amputations for chronic limb threatening ischaemia and who had pre-operative CTA, were analysed ex vivo by microCT and histology. A total of 353 histological cross sections were co-registered with microCT and CTA, and classified as: lipid rich (LP, n = 26), fibrous (FP, n = 80), or calcific (CP, n = 247) plaques. CTA and microCT plaque density was calculated in 791 regions of interest as Hounsfield units (HU).
Results
CTA and microCT could identify plaque components that were confirmed by histology such as fibrous tissue (FP), lipid pool/core (LP), and calcification (CP). MicroCT densities were 77.8 HU for FP (IQR 52.8, 129.5 HU), −28.4 HU for LP (IQR −87.1, 13.2 HU), and 3826.0 HU for CP (IQR 2989.0, 4501.0 HU). CTA densities of the three components of the plaque were: 78.0 HU for FP (IQR 59.5, 119.8 HU), 32.5 HU for LP (IQR 15.0, 42 HU), and 641.5 HU for CP (IQR 425.8, 1135 HU). The differences were statistically significant between the HU densitometric characteristics among the three groups (p < .0001) for both imaging modalities. Overall, microCT performed better diagnostically than conventional CTA for the three types of plaques: areas under the receiving operator characteristics curve were greater for microCT than CTA for FP (0.97 vs. 0.90), for LP (0.88 vs. 0.67), and for CP (0.97 vs. 0.90).
Conclusion
CTA and microCT can be used to identify histological atherosclerotic plaque components, with better diagnostic performance for microCT. This study demonstrates the feasibility of using microCT to assess plaque morphology lesions in a manner that approaches histology thus becoming a useful tool for ex vivo assessment of atherosclerosis and towards lesion based treatment.
To the best of the authors' knowledge, this is the first study to assess the co-registration of conventional computed tomography angiography and micro-computed tomography with histology of the popliteal artery from patients with chronic limb threatening ischaemia. Computed tomography angiography accurately assesses fibrous and calcific plaque; however, the lipid rich plaques are the hardest to detect. Micro-computed tomography allows higher accuracy, and can also differentiate microcalcification from sheet and nodular calcification, making it closer to histology; thus allowing lesion categorisation and potentially a more detailed lesion based treatment.
Introduction
Atherosclerotic plaque characterisation and detection has been well studied in coronary arteries,
although understanding of the morphology of peripheral arterial obstructive disease (PAOD) has lagged behind and is based on characteristics described for the coronary arteries which may not be applicable peripherally.
2017 ESC guidelines on the diagnosis and treatment of peripheral arterial diseases, in collaboration with the European Society for Vascular Surgery (ESVS).
Editor's choice – comorbidity patterns among patients with peripheral arterial occlusive disease in Germany: a trend analysis of health insurance claims data.
Although the atherosclerotic process is similar in various vascular beds, the extent and type of plaque, thrombotic events, and presence of medial calcification are different in PAOD compared with coronary arterial disease.
Reliable non-invasive detection and appropriate classification of atherosclerotic plaques in peripheral arterial obstructive lesions would constitute an important step for risk stratification of patients. Non-invasive characterisation of PAOD lesions needs to be refined for any accurate therapeutic decision making, and improving knowledge of the pathology of the lesions will allow a lesion based treatment approach.
Therefore, conventional computed tomography angiography (CTA) has been proposed as a non-invasive tool for characterisation of atherosclerotic plaques. MicroCT is an ex vivo and in vivo (in small animals) tomographic imaging modality with micrometre resolution and scanning efficiency,
moreover the latter can only be performed once and in a single direction (choosing between longitudinal or cross sectional), therefore it is destructive, time consuming, and expensive.
Although pathological analysis will remain the gold standard, because of its high accuracy and spatial resolution, microCT with two and three dimensional information might be a useful tool for better understanding PAOD. Indeed, plaque morphology imaging by microCT provides lesion characterisation that should allow a lesion based treatment approach; from choosing the best therapeutic strategy (open vs. endovascular, anterograde vs. retrograde access) to choosing the best implant (stent design, but, moreover, stents adapted to specific lesions).
This study aimed to co-register CTA, with microCT and histology of atherosclerotic plaques obtained from patients with chronic limb threatening ischaemia (CLTI).
Materials and methods
Study population
This was a prospective observational study, using 12 popliteal arteries removed from amputated legs from 11 patients who had had CTA prior to transfemoral amputations, obtained from the GEPROVAS collaborative retrieval programme (Strasbourg, France) and assessed by microCT and histology. All patients had a diagnosis of CLTI (rest pain, gangrene, or foot ulcer of more than two weeks) with or without superimposed acute limb ischaemia (sudden decrease in arterial perfusion of the limb of less than two weeks).
The study was approved by the institutional review board at the University Hospital of Strasbourg, France (2018-A03406-49) and Cardiovascular Pathology Institute (Gaithersburg, MD, USA).
CTA imaging and microCT imaging
CTAs were acquired in all cases on a 320 row CT scanner (Aquilion One, Canon Medical Systems, Japan). MicroCTs of dissected vessels were performed at CVPath Institute, Inc, (Gaithersburg, MD, USA) using a Nikon X-Tek XT H 225ST MicroCT system with a Perkin Elmer PE1621 EHS 2000x2000 X-ray detector panel (Nikon Metrology, Brighton, MI, USA). Details of the two procedures are available in the Supplementary material.
Histology processing for popliteal arteries
Imaged popliteal arterial segments were processed as described previously.
2017 ESC guidelines on the diagnosis and treatment of peripheral arterial diseases, in collaboration with the European Society for Vascular Surgery (ESVS).
In brief, the samples were decalcified in EDTA, and then cut into 3 cm segments, dehydrated and sectioned at 3–4 mm intervals before being embedded in paraffin. Each paraffin embedded block was cut at 4–6 microns and stained with hematoxylin and eosin and modified Movat pentachrome stains.
Co-registration of CTA with microCT images and histology
All CTA images were co-registered with radiographs, microCT, and histological sections. Images were co-registered using side branches as index markers, with consideration given to the measured distance along the longitudinal axis and careful attention given to the shrinkage artefacts from fixation and dehydration. Longitudinal and circumferential adjustments were made using anatomical landmarks such as calcification and luminal configuration, to detect the same plaque on the CTA image as on the microCT image.
Evaluation of CTA, microCT, and histological cross sectional images
CTA and microCT were reviewed by both techniques blinded to the histological findings, by two investigators (S.K and H.J.). All histology slides were reviewed by two investigators (S.T. and R.V.), blinded to the imaging findings. Popliteal plaques were classified using the modified American Heart Association classification scheme:
1) adaptive intimal thickening or fibrous plaque, defined as lesions with predominantly fibrous tissue; 2) pathological intimal thickening defined as plaques containing lipid pools, or fibro-atheroma defined as plaques containing a necrotic core with or without macrophages and/or lymphocytic infiltration, and/or mild calcification; and 3) fibrocalcific plaque, defined as burnt out lesions with severe calcification with or without a necrotic core. The histological section underwent morphometric analysis (Zen2, Zeiss, Oberkochen, Germany). The lumen and internal elastic lamina (IEL) and external elastic lamina (EEL) were traced manually, and the corresponding areas were calculated. Plaque area and per cent stenosis were determined using the following formula: (plaque area = [IEL area-lumen area]; and % area stenosis = [plaque area/IEL area]∗100). The CTA and microCT cross sectional images were independently assessed and classified according to the following scheme: fibrous plaque (homogeneous dense signal), calcific plaque (hyperdense region), and lipid rich plaque (hypodense region), blinded to the histological findings.
Multiple regions of interest (ROI) in each plaque and lumen were located on the cross sectional image, and the density of the ROI measured (expressed by Hounsfield units [HU] for both techniques and additionally in grey value for microCT). To confirm the accuracy of CT and microCT for evaluating plaque characteristics, the minimum size of ROI was used in this study, 1 mm × 1 mm pixel for CTA and 20 μm/voxel for microCT. The densities of the ROIs in the lumen, lipid, fibrous, and calcified plaques were compared. Further details are described in the Supplementary material.
Statistical analysis
Values were expressed as median (interquartile range, IQR). The gold standard for plaque evaluation was histology. Statistical comparisons were performed by Kruskal–Wallis test for evaluating differences in measurement parameters. A p value < .050 was considered statistically significant. Sensitivity, specificity, positive, negative predictive value, and accuracy (corresponding to the probability that the data are correctly classified, expressed as a percentage, and calculated as = Sensitivity × Prevalence + Specificity × [1 – Prevalence]), as well as disease prevalence were expressed as percentages. Confidence intervals for these parameters were “exact” Clopper-Pearson confidence intervals. Confidence intervals for the likelihood ratios were calculated using the Log method as given by Altman et al.
For evaluation of inter- and intra-observer variation in interpretation, CTA and microCT findings were recorded by the observers blindly and analysed with Cohen's kappa statistic. ROC curves were calculated for both technologies for detection of each type of plaque using R software, and comparison of receiver operating characteristic (ROC) curves was tested with the method of DeLong et al.
JMP version 13.0 (SAS Institute, Cary, North Carolina) was used for statistical analysis.
Results
Study population
Eleven patients (10 men, one woman) with a median age of 65.5 years (IQR, 55.6–85.4 years) had undergone above knee amputation; 12 popliteal arteries (one patient had bilateral amputations) were harvested with a median length of 13.7 cm (IQR 11.9, 17.5 cm). Demographics are shown in Table 1. A total of 353 histological cross sections was examined and co-registered with CTA and microCT cross sections.
Table 1Characteristics of 11 patients and 12 popliteal arteries studied for co-registration of atherosclerotic plaques by conventional computed tomography (CT) angiography, microCT and histology
n = 12 as one patient had two amputations with femoral lesions.
Aorto-iliac
2 (16.7)
Femoral
8 (66.6)
Popliteal
2 (16.7)
Crural
12 (100)
Cause of amputation
ALI on CLTI
2 (18.2)
CLTI
9 (81.2)
Arteries
12
Length – cm
13.7 (11.9–17.5)
Stenosis – %
88.2 (71.3–98.7)
Bone formation
8 (66.7)
Histological characteristics of vessels
Chronic total occlusion
3 (36.0)
Calcified nodule
4 (48.0)
Nodular calcification
2 (24.0)
Rupture
2 (24.0)
Severe intimal proliferation
1 (12.0)
Data are presented as n (%) or median (interquartile range). APT = antiplatelet therapy; DAPT = dual antiplatelet therapy; ALI = acute limb ischaemia, CLTI = chronic limb threatening ischaemia.
∗ n = 12 as one patient had two amputations with femoral lesions.
Histopathological characteristics of popliteal plaques
Histological evaluation showed adaptive intimal thickening and fibrous plaque in 80 sections (22.7%), pathological intimal thickening and fibro-atheroma in 26 (7.4%), and fibrocalcific (predominantly calcium) plaques in 247 (69.9%) (Table 2). Median per cent stenosis at the severest site of stenosis was 82.2% (IQR 71.3, 98.7%). Chronic total occlusions were observed in three vessels, calcified nodules in four, nodular calcifications in two, rupture in two (one spontaneous and one possibly related to a previous embolectomy, performed 24 days before), and severe intimal proliferation (restenosis) in one case. Bone formation was observed in eight of 12 vessels (66.7%). The arch of intimal calcification was 175.0° (IQR 88.6, 275.8°), mostly as nodular calcifications, and for medial calcification 82.5° (IQR 45.5, 178°), mostly as nodular calcification, with no significant differences between the two (p = .20) (Fig. S1).
Table 2Assessment of atherosclerotic plaque morphologies originating from 12 popliteal arteries by computed tomography angiography (CTA) and microCT compared with 353 histological cross sections of the lesions
Histology
CTA
MicroCT
Fibrous
Lipid rich
Calcific
Total
Fibrous
Lipid rich
Calcific
Total
AIT
4
0
1
5
5
0
0
5
Fibrous
58
10
7
75
71
2
2
75
PIT/FA
16
10
0
26
2
20
4
26
Fibrocalc
27
6
214
247
3
0
244
247
Total
105
26
222
353
81
22
250
353
Data are presented as n. AIT = adaptive intimal thickening; PIT = pathological intimal thickening; FA = fibro-atheroma; Fibrocalc = fibrocalcific.
Overall, CTA had the ability to recognise the basic plaque morphologies such as fibrous tissue, lipid and calcification regions (Fig. 1). The CTA diagnostic accuracy was 82.7% for fibrous plaques (95% CI 78.3%–86.5%), 90.9% for lipid rich plaques (95% CI 87.4%–93.7%), and 88.4% for calcific plaques (95% CI 84.6%–91.5%). However, there were some discrepancies between histology and CTA; lipid rich plaque detection with CTA had a sensitivity of 38.5% (95% CI 20.2%–59.4%), whereas for calcific and fibrous plaque the sensitivity was greater, 86.6% (95% CI 81.8%–90.6%) and 77.5% (95% CI 66.8%–86.1%), respectively (Fig. 2). Indeed, 16 (61.5%) lipid rich plaques were classified as fibrous plaques. Moreover, the calcification characteristics of nodular and microcalcification could not be identified by CTA, because of limited resolution and blooming artefacts (Fig. S2). Also, 27 (10.9%) of the fibrocalcific plaques were misclassified as fibrous plaques because of the small size of the calcification that could not be identified by CTA.
Figure 1Atherosclerotic characterisation of fibrous (A), calcific (B), and lipid (C) plaques of the popliteal artery with co-registration between computed tomography angiography (CTA; a-b, g-h, m-n) and microCT (c-d, i-j, o-p) with histology (e-f, k-l, q-r) in longitudinal (a, c, g, i, m, o) and axial (b, d, h, j, n, p) views. Histological cross sections (e, k, q) with high power images (f, l, r) show microcalcifications (arrowheads) of the fibrous plaque (e–f) spotted also by microCT (d); sheet and nodular calcification in the calcific plaque (k–l) of chronic total occlusion, and areas of necrotic core in a lipid rich plaque (q–r). Lu = lumen; Ca++ = calcification.
Figure 2Multimodality imaging of a lipid rich plaque originating from the popliteal artery (A) of a 57 year old man showing mild calcifications (B) in radiographic images by the co-registration between computed tomography angiography (CTA) (C–E) and microCT (F–H) with histology (I, J). The longitudinal view in CTA (C) and microCT (F) corresponds to the boxed area in B and the cross sections (D–E, G–H) corresponds to the lines in C and F, respectively, demonstrating the contrast filled lumen (Lu) and the hypodense regions (arrowheads) corresponding to the lipid pools shown in histology (I, J). Ca++ = calcification.
On the other hand, microCT also had a high diagnostic accuracy for all three plaque types (fibrous plaque 97.5% [95% CI 95.2%–98.8%], lipid rich plaque 98.0% [95% CI 96.0%–99.2%], and calcific plaques 97.5% [95% CI 95.2%–98.8%]). Lipid rich plaques were misdiagnosed in six cases (23.0%) (Fig. S3). Nevertheless, the sensitivity for lipid rich plaque detection was greater in microCT than CTA, improving from 38.5% to 76.9% (95% CI 56.4%–91.0%), with the result that the positive predictive value (PPV) was 95.2% (95% CI 73.6%–99.3%), and the negative PV (NPV) was 98.2% (95% CI 73.6%–99.3%) (Table 3). Lastly, microCT had better diagnostic performances than conventional CTA for the three plaque types: areas under the curve (AUC) were greater for microCT than CTA for fibrous plaque (FP) (0.97 vs. 0.90), for lipid plaque (LP) (0.88 vs. 0.67), and for calcified plaque (CP) (0.97 vs. 0.90) (Fig. 3).
Table 3Atherosclerotic plaque detection, positive (PPV) and negative (NPV) predictive values, sensitivity and specificity of computed tomography angiography (CTA) and microCT for the detection of different plaque morphologies in 12 popliteal arteries
Imaging modality
Fibrous plaque
Lipid rich plaque
Calcific plaque
CTA
PPV
59.05 (51.68–66.03)
38.46 (24.02–55.27)
96.40 (93.20–98.12)
NPV
92.74 (89.5–95.06)
95.11 (93.48–96.35)
74.81 (68.27–80.39)
Sensitivity
77.50 (66.79–86.09)
38.46 (20.23–59.43)
86.64 (81.75–90.62)
Specificity
84.25 (79.38–88.36)
95.11 (92.18–97.18)
92.45 (85.67–96.69)
Diagnostic accuracy
82.72 (78.36–86.52)
90.93 (87.44–93.72)
88.39 (84.57–91.53)
MicroCT
PPV
93.83 (86.43–97.32)
95.24 (73.64–99.31)
97.60 (94.92–98.88)
NPV
98.53 (96.27–99.43)
98.19 (73.64–99.31)
97.09 (91.04–99.04)
Sensitivity
95.00 (87.69–98.62)
76.92 (56.35–91.03)
98.79 (96.49–99.75)
Specificity
98.17 (95.78–99.40)
99.69 (93.31–99.99)
94.34 (88.09–97.89)
Diagnostic accuracy
97.45 (95.22–98.83)
98.02 (95.96–99.20)
97.45 (95.22–98.83)
Data are presented as % (95% confidence interval).
Figure 3Receiver operating characteristic curves of diagnostic performance of computed tomography angiography (CTA) and microCT for detection of fibrous (A), calcific (B), and lipid rich (C) plaques; p < .001 for the three types of plaques. AUC = area under the curve, CI = confidence interval.
CTA could not differentiate nodular from sheet calcifications. However, the ability of microCT to differentiate nodular calcifications from sheet calcifications was highly accurate; sensitivity was 95.9% (95% CI 91.7%–98.3%), specificity was 84.4% (95% CI 74.3%–91.7%), and the diagnostic accuracy was 92.3% (95% CI 88.3%–95.3%) (Fig. 4).
Figure 4Different type of calcium in the popliteal artery of an 85 year old woman (A, faxitron radiograph [Specimen Radiography System]) in comparison between computed tomography angiography (CTA; B, D–E) and microCT (C, F–G) of the boxed area in A, and histology (H, I) showing chronic total occlusion with calcified plaque with nodular calcifications (H) that almost occlude the lumen and (I) mostly sheet calcium. The two types of calcium cannot be defined in the 3D reconstructions of the CTA (B), but microCT (C) shows a high definition of the calcific plaques, including the spatial arrangement between sheet and nodular calcification within the plaque. The cross sections of CTA (D–E), microCT (F–G), and histology (H–I) are at two levels demonstrated in B and C (red and blue).
Details of inter- and intra-observer agreement and cut off detection values are reported in the Supplementary material.
Densitometric characterisation of CTA and microCT
A total of 353 plaques was examined by CTA and microCT, and 791 ROI were identified in the plaque and lumen by CTA and microCT images; two ROI per plaque corresponding to 160 ROI located on fibrous plaques, 52 on lipid plaques, 494 on calcified plaques, and 85 additional ROI were placed within the lumen. Using CTA, fibrous plaque had a median density of 78.0 HU (IQR 59.5, 119.8 HU), lipid rich plaques 32.5 HU (IQR 15.0, 42.0 HU), and calcified plaques 641.5 HU (IQR 425.8, 1135 HU). Lumen density was evaluated as 357.0 HU on the contrast enhanced sequence (IQR 305.0, 450.0 HU). There was a statistically significant difference among the three plaque types and lumen density as determined by CTA (p < .0001).
Using microCT, fibrous plaque had a median density of 77.8 HU (IQR 52.8, 129.5 HU), lipid rich plaques a median density of −28.4 HU (IQR −87.1, 13.2 HU), and calcified plaques a median density of 3826.0 HU (IQR 2989.0, 4501 HU). Lumen density was evaluated (only when the lumen was easily discernible) as −689.3 HU (IQR −732.7, −618.3 HU). There was a statistically significant difference among the three plaques and lumen density as determined by microCT (p < .0001); data are shown in Fig. 5, and in grey scale value in Fig. S4. Among the non-fibrocalcific plaques, the sections showing predominantly microcalcifications were selected to evaluate the HU corresponding to smaller fragment of calcification. Forty-six ROI were co-registered, and the median density was 434.1 HU (IQR 300.3, 1191 HU). With microCT, differences between soft tissue and calcific areas were easier to detect because of the discrete delineation of calcium without any blooming artefacts (Fig. S5). The comparison between imaging modalities revealed significant differences for lipid and calcium but these were similar in fibrous plaques because HU in microCT were set for fibrous tissues (p = .23).
Figure 5Computed tomography angiography (CTA; A) and microCT (B) analysis in comparison of the region of interest (ROI) Hounsfield unit (HU) densities between the three types of plaques and lumen. In total 791 ROI were identified; two ROI per plaque corresponding to 160 ROI located on fibrous plaques, 52 on lipid plaques, 494 on calcified plaques, and 85 on the lumen, with a statistical difference between the four groups for both the CTA values and microCT (p <.001, non-parametric Kruskal–Wallis test). Lines within boxes represent median values; the upper and lower lines of the boxes represent the 75th and 25th percentiles, respectively; the upper and lower bars outside the boxes represent the maximum and minimum values, respectively.
To the best of the present authors' knowledge, this is the first study to assess the co-registration of CTA and microCT with popliteal artery histology from patients with CLTI. The main findings of the current study are: 1) CTA can recognise plaque components (i.e., fibrous, lipid rich, and calcific regions) in patients with PAOD, although lipid rich plaques are the most difficult category to detect; 2) microCT can recognise all three with high accuracy, especially for calcification; 3) microCT can differentiate nodular calcifications from sheet calcifications; and 4) the most frequent atherosclerotic popliteal plaques were fibrocalcific plaques. They were observed in 70% of sections, whereas a recently published study from the present study group on asymptomatic individuals with high a prevalence of risk factors for atherosclerosis observed fibrocalcific plaques in <30% of all sections examined.
2017 ESC guidelines on the diagnosis and treatment of peripheral arterial diseases, in collaboration with the European Society for Vascular Surgery (ESVS).
The present results indicate that CTA is an adequate non-invasive imaging tool to discriminate different plaque morphologies, with limitations. Overall, CTA could discriminate plaque components such as fibrous, lipid pool, and calcification with 75%–94% accuracy; however, the sensitivity for lipidic plaque was low (38%). These findings corroborate the findings of a recent study by Kolossváry et al. comparing ex vivo coronary CTA to histology; expert visual assessment of CTA showed moderate diagnostic performance for detection of advanced atherosclerotic lesions, i.e. lipid rich plaques.
However, those authors excluded heavily calcified lesions. In the present study, most of the plaques were from patients undergoing amputation, therefore implying that the calcifications were extensive, which might explain a better global accuracy. In popliteal arteries, the extent of calcification is diffuse with extensive blooming artefacts, therefore interfering with the interpretations of other types of plaques by CTA. Similarly, sheet calcification cannot be separated from nodular calcification by CTA but is best separated by microCT.
Densitometric plaque characterisation with conventional CTA and microCT
Concerning CTA, two publications showed similar ranges of densities to the present study (lipid rich plaque was <50 HU, fibrous 50–119 HU, and calcified plaques > 120 HU); however, both studies lacked the histological analysis as gold standard to assess different types of plaques, using intravascular ultrasound instead.
In the present study, PAOD showed a similar range for all three plaques, although the HU for calcific plaques were higher in peripheral arteries than in the coronaries, which may be because of the presence of dense thick calcified sheets.
MicroCT and histology
To the best of the authors' knowledge, only one publication has reported comparison of microCT with histology using 10 atherosclerotic coronary arteries of length 2.5–3.5 cm.
MicroCT qualitatively accurately assessed plaque morphology; however, the quantitative histomorphometric analysis revealed smaller IEL, plaque and lumen areas by histology compared with microCT, because of vessel shrinkage during fixation and the dehydration used for paraffin sectioning. Using grey scale values, those authors observed significant statistical differences between the three types of plaques. Similarly, the present authors also performed grey scale analysis for fibrous, lipid, and calcific plaques and the results showed a similar range of grey values. However, the HU were also calculated and results presented for the three types of components, and the HU for FP were comparable to CTA. However, for calcified areas the HU had extremely high values (∼3000 HU) by microCT, which can be explained by the difference in acquisition between CTA and microCT.
MicroCT, a step closer to histological characterisation and to clinical applications
The use of microCT imaging has increased in experimental animal studies and in ex vivo human specimens in the last decade.
This study has demonstrated the technical feasibility of using microCT for assessment of peripheral atherosclerotic plaques, ex vivo. It is a rapid method for evaluation of atherosclerotic lesions, with higher resolution than CTA (with the ability to detect microcalcification). Images can be projected in 3D with microCT with suitable software, whereas histology is cumbersome, requires serial sectioning and the need for landmarks, which is expensive. Conventional histological analysis has its constraints and microCT imaging could become a non-invasive solution to alleviate some of these; however, to date, no antibody co-localisation for identification of various antigens has been performed. Other non-invasive imaging modalities have characterised PAOD lesions, e.g., Becker et al. used xray spectroscopy to compare fundamental changes in intracellular elemental compositions between control, claudicants, and critical limb ischaemia muscle tissue.
The study showed that intracellular magnesium and calcium were lower in PAOD compared with control myofibres, whereas sulphur was higher. A combination of microCT with evaluation of the muscles of the ischaemic leg could lead to greater accuracy and better understanding of PAOD. A more accurate histopathological diagnosis and better plaque characterisation are necessary to identify lesions that need specific treatment, leading to improved patient care. In a recent study, Torii et al. showed that calcifications have an impact on delayed healing in newer generation drug eluting stents: severe calcification of stented arteries caused delayed healing of the stented lesion and luminal surface calcified area in direct contact with stent strut was an independent predictor of delayed strut coverage in the newer generation drug eluting stents.
Therefore, plaque characterisation, although challenging, is a crucial step, and non-invasive imaging might be the key to access lesion based treatment.
Study limitations
wThere are some limitations to the image quality with CTA and density may vary depending on the tube voltage and the contrast media concentration. To ensure accurate co-registration of plaques by CTA, microCT, and histology, landmarks such as the origin of side branches and their relation to the target lesions were used and confirmed by two observers; however, there remains the possibility of location misalignment. Finally, the total number of specimens was small, and plaques were not as variable as seen in patients who present with claudication vs. CLTI.
Conclusion
In vivo CTA and ex vivo microCT of popliteal human arteries were used to differentiate and recognise different microstructures of atherosclerotic peripheral artery plaque characteristics. The study demonstrated the feasibility of using microCT to assess morphological characteristics of atherosclerotic lesions in a manner that approaches histology; thus becoming an indispensable tool for ex vivo assessment of atherosclerosis.
Funding
The study was funded by CVPath Institute and GEPROVAS.
Conflict of interest
R.V. and A.V.F. have received institutional research support from NIH (HL141425), Leducq Foundation Grant; 480 Biomedical; 4C Medical; 4Tech; Abbott; Accumedical; Amgen; Biosensors; Boston Scientific; Cardiac Implants; Celonova; Claret Medical; Concept Medical; Cook; CSI; DuNing, Inc; Edwards LifeSciences; Emboline; Endotronix; Envision Scientific; Lutonix / Bard; Gateway; Lifetech; Limflo; MedAlliance; Medtronic; Mercator; Merill; Microport Medical; Microvention; Mitraalign; Mitra assist; NAMSA; Nanova; Neovasc; NIPRO; Novogate; Occulotech; OrbusNeich Medical; Phenox; Profusa; Protembis; Qool; ReCor; Senseonics; Shockwave; Sinomed; Spectranetics; Surmodics; Symic; Vesper; W.L. Gore; Xeltis. A.V.F. has received honoraria from Abbott Vascular; Biosensors; Boston Scientific; Celonova; Cook Medical; CSI; Lutonix Bard; Sinomed; Terumo Corporation; and is a consultant to Amgen; Abbott Vascular; Boston Scientific; Celonova; Cook Medical; Lutonix Bard; Sinomed. R.V. has received honoraria from Abbott Vascular; Biosensors; Boston Scientific; Celonova; Cook Medical; Cordis; CSI; Lutonix Bard; Medtronic; OrbusNeich Medical; CeloNova; SINO Medical Technology; ReCore; Terumo Corporation; W. L. Gore; Spectranetics; and is a consultant Abbott Vascular; Boston Scientific; Celonova; Cook Medical; Cordis; CSI; Edwards Lifescience; Lutonix Bard; Medtronic; OrbusNeich Medical; ReCore; Sinomededical Technology; Spectranetics; Surmodics; Terumo Corporation; W. L. Gore; Xeltis. S.T. received research grants from SUNRISE lab. A.C. receives research grants from University Hospital RWTH Aachen. However, none of these entities provided financial support for this study. The other authors declare no competing interests.
Appendix A. Supplementary data
The following are the Supplementary data to this article:
2017 ESC guidelines on the diagnosis and treatment of peripheral arterial diseases, in collaboration with the European Society for Vascular Surgery (ESVS).
Editor's choice – comorbidity patterns among patients with peripheral arterial occlusive disease in Germany: a trend analysis of health insurance claims data.
To submit a comment for a journal article, please use the space above and note the following:
We will review submitted comments as soon as possible, striving for within two business days.
This forum is intended for constructive dialogue. Comments that are commercial or promotional in nature, pertain to specific medical cases, are not relevant to the article for which they have been submitted, or are otherwise inappropriate will not be posted.
We require that commenters identify themselves with names and affiliations.
30778-4&id=gr1.jpg){kind=link}
30778-4&id=gr2.jpg){kind=link}
30778-4&id=gr3.jpg){kind=link}
30778-4&id=gr4.jpg){kind=link}
30778-4&id=gr5.jpg){kind=link}
30778-4&id=figs1.jpg){kind=link}
30778-4&id=figs2.jpg){kind=link}
30778-4&id=figs3.jpg){kind=link}
30778-4&id=figs4.jpg){kind=link}
30778-4&id=figs5.jpg){kind=link}