Computed tomography angiography in microsurgery: indications, clinical utility, and pitfalls

OBJECTIVE

Computed tomographic angiography (CTA) can be used to obtain 3-dimensional vascular images and soft-tissue definition. The goal of this study was to evaluate the reliability, usefulness, and pitfalls of CTA in preoperative planning of microvascular reconstructive surgery.

METHODS

A retrospective review of patients who obtained preoperative CTA in preparation for planned microvascular reconstruction was performed over a 5-year period (2001-2005). The influence of CTA on the original operative plan was assessed for each patient, and CTA results were correlated to the operative findings.

RESULTS

Computed tomographic angiography was performed on 94 patients in preparation for microvascular reconstruction. In 48 patients (51%), vascular abnormalities were noted on CTA. Intraoperative findings correlated with CTA results in 97% of cases. In 42 patients (45%), abnormal CTA findings influenced the original operative plan, such as the choice of vessels, side of harvest, or nature of the reconstruction (local flap instead of free tissue transfer). Technical difficulties in performing CTA were encountered in 5 patients (5%) in whom interference from external fixation devices was the main cause.

CONCLUSIONS

This large study of CTA obtained for preoperative planning of reconstructive microsurgery at both donor and recipient sites study demonstrates that CTA is safe and highly accurate. Computed tomographic angiography can alter the surgeon's reconstructive plan when abnormalities are noted preoperatively and consequently improve results by decreasing vascular complication rates. The use of CTA should be considered for cases of microsurgical reconstruction where the vascular anatomy may be questionable.

Uncluttered Single-Image Visualization of Vascular Structures Using GPU and Integer Programming

Direct projection of 3D branching structures, such as networks of cables, blood vessels, or neurons onto a 2D image creates the illusion of intersecting structural parts and creates challenges for understanding and communication. We present a method for visualizing such structures, and demonstrate its utility in visualizing the abdominal aorta and its branches, whose tomographic images might be obtained by computed tomography or magnetic resonance angiography, in a single 2D stylistic image, without overlaps among branches. The visualization method, termed uncluttered single-image visualization (USIV), involves optimization of geometry. This paper proposes a novel optimization technique that utilizes an interesting connection of the optimization problem regarding USIV to the protein structure prediction problem. Adopting the integer linear programming-based formulation for the protein structure prediction problem, we tested the proposed technique using 30 visualizations produced from five patient scans with representative anatomical variants in the abdominal aortic vessel tree. The novel technique can exploit commodity-level parallelism, enabling use of general-purpose graphics processing unit (GPGPU) technology that yields a significant speedup. Comparison of the results with the other optimization technique previously reported elsewhere suggests that, in most aspects, the quality of the visualization is comparable to that of the previous one, with a significant gain in the computation time of the algorithm.

Automated tracing of the adventitial contour of aortoiliac and peripheral arterial walls in CT angiography (CTA) to allow calculation of non-calcified plaque burden

Aortoiliac and lower extremity arterial atherosclerotic plaque burden is a risk factor for the development of visceral and peripheral ischemic and aneurismal vascular disease. While prior research allows automated quantification of calcified plaque in these body regions using CT angiograms, no automated method exists to quantify soft plaque. We developed an automatic algorithm that defines the outer wall contour and wall thickness of vessels to quantify non-calcified plaque in CT angiograms of the chest, abdomen, pelvis, and lower extremities. The algorithm encodes the search space as a constrained graph and calculates the outer wall contour by deriving a minimum cost path through the graph, following the visible outer wall contour while minimizing path tortuosity. Our algorithm was statistically equivalent to a reference standard made by two reviewers. Absolute error was 1.9 ± 2.3% compared to the inter-observer variability of 3.9 ± 3.6%. Wall thickness in vessels with atherosclerosis was 3.4 ± 1.6 mm compared to 1.2 ± 0.4 mm in normal vessels. The algorithm shows promise as a tool for quantification of non-calcified plaque in CT angiography. When combined with previous research, our method has the potential to quantify both non-calcified and calcified plaque in all clinically significant systemic arteries, from the thoracic aorta to the arteries of the calf, over a wide range of diameters. This algorithm has the potential to enable risk stratification of patients and facilitate investigations into the relationships between asymptomatic atherosclerosis and a variety of behavioral, physiologic, pathologic, and genotypic conditions.

Accuracy of a remote eye tracker for radiologic observer studies: effects of calibration and recording environment

RATIONALE AND OBJECTIVES

To determine the accuracy and reproducibility of a remote eye-tracking system for studies of observer gaze while displaying volumetric chest computed tomography (CT) images.

MATERIALS AND METHODS

Four participants performed calibrations using three different gray-scale backgrounds (black, gray, and white). Each participant then observed a three-dimensional 10-point test pattern embedded in five Digital Imaging and Communications in Medicine (DICOM) datasets (test backgrounds): a full 190-section chest CT scan, 190 copies of a single chest CT section, and three 190-section datasets of homogeneous intensity (black, gray, and white).

RESULTS

Significant variances between participants, calibration backgrounds, and test backgrounds were observed. The least mean systematic error (deviation of recorded gaze position from target) was obtained when the calibration background and test background were black (27 pixels). Systematic error increased when displaying a test background that deviated from the calibration background intensity. Hence, the largest mean systematic error occurred when calibrating to a black background and displaying a white background (67 pixels). For complex chest CT volumes the white calibration background performed best (38 pixels). An angular analysis of the systematic error was performed and demonstrated that the systemic error primarily affects the vertical position of the estimated gaze position.

CONCLUSION

Our findings indicate a potential source of systematic error during gaze recording in a dynamic environment and highlight the importance of configuring the calibration procedure according to the brightness of the display. We recommend that investigators develop routines for postcalibration accuracy measurement and report the effective accuracy for the display environment in which the data are collected.

CT patterns of fungal pulmonary infections of the lung: comparison of standard-dose and simulated low-dose CT

PURPOSE

To assess the effect of radiation dose reduction on the appearance and visual quantification of specific CT patterns of fungal infection in immuno-compromised patients.

MATERIALS AND METHODS

Raw data of thoracic CT scans (64 × 0.75 mm, 120 kVp, 300 reference mAs) from 41 consecutive patients with clinical suspicion of pulmonary fungal infection were collected. In 32 patients fungal infection could be proven (median age of 55.5 years, range 35-83). A total of 267 cuboids showing CT patterns of fungal infection and 27 cubes having no disease were reconstructed at the original and 6 simulated tube currents of 100, 40, 30, 20, 10, and 5 reference mAs. Eight specific fungal CT patterns were analyzed by three radiologists: 76 ground glass opacities, 42 ground glass nodules, 51 mixed, part solid, part ground glass nodules, 36 solid nodules, 5 lobulated nodules, 6 spiculated nodules, 14 cavitary nodules, and 37 foci of air-space disease. The standard of reference was a consensus subjective interpretation by experts whom were not readers in the study.

RESULTS

The mean sensitivity and standard deviation for detecting pathological cuboids/disease using standard dose CT was 0.91 ± 0.07. Decreasing dose did not affect sensitivity significantly until the lowest dose level of 5 mAs (0.87 ± 0.10, p=0.012). Nodular pattern discrimination was impaired below the dose level of 30 reference mAs: specificity for fungal 'mixed nodules' decreased significantly at 20, 10 and 5 reference mAs (p<0.05). At lower dose levels, classification drifted from 'solid' to 'mixed nodule', although no lesion was missed.

CONCLUSION

Our simulation data suggest that tube current levels can be reduced from 300 to 30 reference mAs without impairing the diagnostic information of specific CT patterns of pulmonary fungal infections.

Shape "break-and-repair" strategy and its application to automated medical image segmentation

In three-dimensional medical imaging, segmentation of specific anatomy structure is often a preprocessing step for computer-aided detection/diagnosis (CAD) purposes, and its performance has a significant impact on diagnosis of diseases as well as objective quantitative assessment of therapeutic efficacy. However, the existence of various diseases, image noise or artifacts, and individual anatomical variety generally impose a challenge for accurate segmentation of specific structures. To address these problems, a shape analysis strategy termed "break-and-repair" is presented in this study to facilitate automated medical image segmentation. Similar to surface approximation using a limited number of control points, the basic idea is to remove problematic regions and then estimate a smooth and complete surface shape by representing the remaining regions with high fidelity as an implicit function. The innovation of this shape analysis strategy is the capability of solving challenging medical image segmentation problems in a unified framework, regardless of the variability of anatomical structures in question. In our implementation, principal curvature analysis is used to identify and remove the problematic regions and radial basis function (RBF) based implicit surface fitting is used to achieve a closed (or complete) surface boundary. The feasibility and performance of this strategy are demonstrated by applying it to automated segmentation of two completely different anatomical structures depicted on CT examinations, namely human lungs and pulmonary nodules. Our quantitative experiments on a large number of clinical CT examinations collected from different sources demonstrate the accuracy, robustness, and generality of the shape "break-and-repair" strategy in medical image segmentation.

Right coronary wall CMR in the older asymptomatic advance cohort: positive remodeling and associations with type 2 diabetes and coronary calcium

BACKGROUND

Coronary wall cardiovascular magnetic resonance (CMR) is a promising noninvasive approach to assess subclinical atherosclerosis, but data are limited in subjects over 60 years old, who are at increased risk. The purpose of the study was to evaluate coronary wall CMR in an asymptomatic older cohort.

RESULTS

Cross-sectional images of the proximal right coronary artery (RCA) were acquired using spiral black-blood coronary CMR (0.7 mm resolution) in 223 older, community-based patients without a history of cardiovascular disease (age 60-72 years old, 38% female). Coronary measurements (total vessel area, lumen area, wall area, and wall thickness) had small intra- and inter-observer variabilities (r = 0.93~0.99, all p < 0.0001), though one-third of these older subjects had suboptimal image quality. Increased coronary wall thickness correlated with increased coronary vessel area (p < 0.0001), consistent with positive remodeling. On multivariate analysis, type 2 diabetes was the only risk factor associated with increased coronary wall area and thickness (p = 0.03 and p = 0.007, respectively). Coronary wall CMR measures were also associated with coronary calcification (p = 0.01-0.03).

CONCLUSIONS

Right coronary wall CMR in asymptomatic older subjects showed increased coronary atherosclerosis in subjects with type 2 diabetes as well as coronary calcification. Coronary wall CMR may contribute to the noninvasive assessment of subclinical coronary atherosclerosis in older, at-risk patient groups.

ACCF/SCCT/ACR/AHA/ASE/ASNC/NASCI/SCAI/SCMR 2010 Appropriate Use Criteria for Cardiac Computed Tomography. A Report of the American College of Cardiology Foundation Appropriate Use Criteria Task Force, the Society of Cardiovascular Computed Tomography, the American College of Radiology, the American Heart Association, the American Society of Echocardiography, the American Society of Nuclear Cardiology, the North American Society for Cardiovascular Imaging, the Society for Cardiovascular Angiography and Interventions, and the Society for Cardiovascular Magnetic Resonance

The American College of Cardiology Foundation (ACCF), along with key specialty and subspecialty societies, conducted an appropriate use review of common clinical scenarios where cardiac computed tomography (CCT) is frequently considered. The present document is an update to the original CCT/cardiac magnetic resonance (CMR) appropriateness criteria published in 2006, written to reflect changes in test utilization, to incorporate new clinical data, and to clarify CCT use where omissions or lack of clarity existed in the original criteria (1). The indications for this review were drawn from common applications or anticipated uses, as well as from current clinical practice guidelines. Ninety-three clinical scenarios were developed by a writing group and scored by a separate technical panel on a scale of 1 to 9 to designate appropriate use, inappropriate use, or uncertain use. In general, use of CCT angiography for diagnosis and risk assessment in patients with low or intermediate risk or pretest probability for coronary artery disease (CAD) was viewed favorably, whereas testing in high-risk patients, routine repeat testing, and general screening in certain clinical scenarios were viewed less favorably. Use of noncontrast computed tomography (CT) for calcium scoring was rated as appropriate within intermediate- and selected low-risk patients. Appropriate applications of CCT are also within the category of cardiac structural and functional evaluation. It is anticipated that these results will have an impact on physician decision making, performance, and reimbursement policy, and that they will help guide future research.

ACCF/SCCT/ACR/AHA/ASE/ASNC/NASCI/SCAI/SCMR 2010 Appropriate Use Criteria for Cardiac Computed Tomography. A Report of the American College of Cardiology Foundation Appropriate Use Criteria Task Force, the Society of Cardiovascular Computed Tomography, the American College of Radiology, the American Heart Association, the American Society of Echocardiography, the American Society of Nuclear Cardiology, the North American Society for Cardiovascular Imaging, the Society for Cardiovascular Angiography and Interventions, and the Society for Cardiovascular Magnetic Resonance

The American College of Cardiology Foundation (ACCF), along with key specialty and subspecialty societies, conducted an appropriate use review of common clinical scenarios where cardiac computed tomography (CCT) is frequently considered. The present document is an update to the original CCT/cardiac magnetic resonance (CMR) appropriateness criteria published in 2006, written to reflect changes in test utilization, to incorporate new clinical data, and to clarify CCT use where omissions or lack of clarity existed in the original criteria (1). The indications for this review were drawn from common applications or anticipated uses, as well as from current clinical practice guidelines. Ninety-three clinical scenarios were developed by a writing group and scored by a separate technical panel on a scale of 1 to 9 to designate appropriate use, inappropriate use, or uncertain use. In general, use of CCT angiography for diagnosis and risk assessment in patients with low or intermediate risk or pretest probability for coronary artery disease (CAD) was viewed favorably, whereas testing in high-risk patients, routine repeat testing, and general screening in certain clinical scenarios were viewed less favorably. Use of noncontrast computed tomography (CT) for calcium scoring was rated as appropriate within intermediate- and selected low-risk patients. Appropriate applications of CCT are also within the category of cardiac structural and functional evaluation. It is anticipated that these results will have an impact on physician decision making, performance, and reimbursement policy, and that they will help guide future research.

Automated quantification of aortoaortic and aortoiliac angulation for computed tomographic angiography of abdominal aortic aneurysms before endovascular repair: preliminary study

The degree of angulation of abdominal aortic aneurysms (AAAs) has emerged as an important factor in assessing eligibility for endovascular aneurysm repair (EVAR). The authors developed an automatic algorithm that reduces variability of measurement of aortoiliac angulation. For highly structured manual methods, intraobserver variability was 8.2 degrees ± 5.0 (31% ± 20) and interobserver variability was 5.6 degrees ± 2.5 (20% ± 9.1) compared with 0.6 degrees ± 0.8 (2.2% ± 3.6) (intraobserver) and 0.4 degrees ± 0.4 (1.4% ± 1.9) (interobserver) for the automatic algorithm (P < .01). In phantoms, the automatically measured angles were equivalent to reference values (P < .05). This algorithm was also faster than manual methods and has the potential to enhance the clinical utility and reliability of computed tomographic angiography for preoperative assessment for EVAR.

Assessing operating characteristics of CAD algorithms in the absence of a gold standard

PURPOSE

The authors examine potential bias when using a reference reader panel as "gold standard" for estimating operating characteristics of CAD algorithms for detecting lesions. As an alternative, the authors propose latent class analysis (LCA), which does not require an external gold standard to evaluate diagnostic accuracy.

METHODS

A binomial model for multiple reader detections using different diagnostic protocols was constructed, assuming conditional independence of readings given true lesion status. Operating characteristics of all protocols were estimated by maximum likelihood LCA. Reader panel and LCA based estimates were compared using data simulated from the binomial model for a range of operating characteristics. LCA was applied to 36 thin section thoracic computed tomography data sets from the Lung Image Database Consortium (LIDC): Free search markings of four radiologists were compared to markings from four different CAD assisted radiologists. For real data, bootstrap-based resampling methods, which accommodate dependence in reader detections, are proposed to test of hypotheses of differences between detection protocols.

RESULTS

In simulation studies, reader panel based sensitivity estimates had an average relative bias (ARB) of -23% to -27%, significantly higher (p-value < 0.0001) than LCA (ARB--2% to -6%). Specificity was well estimated by both reader panel (ARB -0.6% to -0.5%) and LCA (ARB 1.4%-0.5%). Among 1145 lesion candidates LIDC considered, LCA estimated sensitivity of reference readers (55%) was significantly lower (p-value 0.006) than CAD assisted readers' (68%). Average false positives per patient for reference readers (0.95) was not significantly lower (p-value 0.28) than CAD assisted readers' (1.27).

CONCLUSIONS

Whereas a gold standard based on a consensus of readers may substantially bias sensitivity estimates, LCA may be a significantly more accurate and consistent means for evaluating diagnostic accuracy.

Incomplete endograft apposition to the aortic arch: bird-beak configuration increases risk of endoleak formation after thoracic endovascular aortic repair

PURPOSE

To determine the clinical importance of the bird-beak configuration after thoracic endovascular aortic repair (TEVAR).

MATERIALS AND METHODS

The institutional review board approved this retrospective study and waived the requirement to obtain informed consent from patients. Sixty-four patients (40 men, 24 women; mean age, 64 years) who underwent TEVAR were evaluated. The treated diseases included dissection (n = 29), degenerative aneurysm (n = 13), acute traumatic transection (n = 8), pseudoaneurysm (n = 4), penetrating aortic ulcer (n = 6), intramural hematoma (n = 2), and mycotic aneurysm (n = 2). Bird-beak configuration, defined as the incomplete apposition of the proximal endograft with a wedge-shaped gap between the device and the aortic wall, was assessed with postprocedural CT angiography. The presence and length of the bird-beak configuration were compared with the formation of endoleaks and adverse clinical events.

RESULTS

Endoleaks were detected in 26 (40%) of the 64 patients, including 14 with type Ia endoleak formation, one with type Ib endoleak formation, six with type II endoleak formation (from the left subclavian artery), two with type IIo endoleak formation (from other arteries), and three with type III endoleak formation. Bird-beak configuration was observed in 28 (44%) of 64 patients and correlated significantly with the risk of developing a type Ia or IIa endoleak (P < .01). Mean bird-beak length was significantly longer (P < .01) in patients with a type Ia or II endoleak (mean length, 14.3 and 13.9 mm, respectively) than in patients without endoleaks (mean length, 8.4 mm). Adverse events included early aortic-related death in three patients, additional treatment for endoleak in eight patients, and stent-graft collapse or infolding in six patients.

CONCLUSION

Detection of bird-beak configuration is helpful in the prediction of adverse clinical events after TEVAR.

Uncluttered single-image visualization of the abdominal aortic vessel tree: method and evaluation

PURPOSE

The authors develop a method to visualize the abdominal aorta and its branches, obtained by CT or MR angiography, in a single 2D stylistic image without overlap among branches.

METHODS

The abdominal aortic vasculature is modeled as an articulated object whose underlying topology is a rooted tree. The inputs to the algorithm are the 3D centerlines of the abdominal aorta, its branches, and their associated diameter information. The visualization problem is formulated as an optimization problem that finds a spatial configuration of the bounding boxes of the centerlines most similar to the projection of the input into a given viewing direction (e.g., anteroposterior), while not introducing intersections among the boxes. The optimization algorithm minimizes a score function regarding the overlap of the bounding boxes and the deviation from the input. The output of the algorithm is used to produce a stylistic visualization, made of the 2D centerlines modulated by the associated diameter information, on a plane. The authors performed a preliminary evaluation by asking three radiologists to label 366 arterial branches from the 30 visualizations of five cases produced by the method. Each of the five patients was presented in six different variant images, selected from ten variants with the three lowest and three highest scores. For each label, they assigned confidence and distortion ratings (low/medium/high). They studied the association between the quantitative metrics measured from the visualization and the subjective ratings by the radiologists.

RESULTS

All resulting visualizations were free from branch overlaps. Labeling accuracies of the three readers were 93.4%, 94.5%, and 95.4%, respectively. For the total of 1098 samples, the distortion ratings were low: 77.39%, medium: 10.48%, and high: 12.12%. The confidence ratings were low: 5.56%, medium: 16.50%, and high: 77.94%. The association study shows that the proposed quantitative metrics can predict a reader's subjective ratings and suggests that the visualization with the lowest score should be selected for readers.

CONCLUSIONS

The method for eliminating misleading false intersections in 2D projections of the abdominal aortic tree conserves the overall shape and does not diminish accurate identifiability of the branches.

Insulin resistance independently predicts the progression of coronary artery calcification

BACKGROUND

Change in coronary artery calcification is a surrogate marker of subclinical coronary artery disease (CAD). In the only large prospective study, CAD risk factors predicted progression of coronary artery calcium (CAC).

METHODS

We measured CAC at enrollment and after 24 months in a community-based sample of 869 healthy adults aged 60 to 72 years who were free of clinical CAD. We assessed predictors of the progression of CAC using univariate and multivariate models after square root transformation of the Agatston scores. Predictors tested included age, sex, race/ethnicity, smoking status, body mass index, family history of CAD, C-reactive protein and several measures of diabetes, insulin levels, blood pressure, and lipids.

RESULTS

The mean age of the cohort was 66 years, and 62% were male. The median CAC at entry was 38.6 Agatston units and increased to 53.3 Agatston units over 24 months (P < .01). The CAC progression was associated with white race, diabetes, dyslipidemia, hypertension, lower diastolic blood pressure, and higher pulse pressure. After controlling for these variables, higher fasting insulin levels independently predicted CAC progression.

CONCLUSIONS

Insulin resistance, in addition to the traditional cardiac risk factors, independently predicts progression of CAC in a community-based population without clinical CAD.

Assessment of the anterior spinal artery and the artery of Adamkiewicz using multi-detector CT angiography

BACKGROUND

Damage to the spinal cord after the treatment of the descending thoracic and thoracoabdominal aortic aneurysms is an uncommon but devastating complication. The artery of Adamkiewicz (AKA) is the principal arterial supply of the anterior spinal artery (ASA) in the lower thoracic and lumbar level. The purpose of this study was to evaluate the visualization of the anterior spinal artery and the artery of Adamkiewicz, the affecting factors for the detection rate using multi-detector row CT (MDCT).

METHODS

Ninety-nine consecutive patients (31 women and 68 men; age range, 25 - 90 years; average age 61.3 years), with suspicion for thoracic aortic lesions necessitating surgical intervention (31 aortic aneurysm, 45 dissection, 5 intramural hematoma, and 18 normal), underwent CT angiography from the aortic arch to the aortic bifurcation. Transverse sections, multiplanar reformations and thin maximum intensity projections were used to assess the ASA and AKA. The level of the ASA and AKA origins and CT acquisition parameters were recorded. The contrast-to-noise ratio of the image, an index of the mass of the T11 body (vertebral mass index), the subcutaneous fat thickness, and the CT value within the aortic arch and at the T11 level were measured. The detection of the ASA and AKA were evaluated relative to the acquisition parameters, scan characteristics, and aortic lesion type. Differences were assessed with the Wilcoxon rank-sum and t tests.

RESULTS

The ASA was visualized in 51 patients (52%) and the AKA in 18 patients (18%). The ASA was identified in 36/67 patients (54%) with 1.25 mm thickness and in 15/32 patients (47%) with 2.5 - 3.0 mm thickness. This difference did not achieve significance (P = 0.13). The detection rate of the ASA and the AKA was influenced by the vertebral mass index and the contrast-to-noise ratio (P < 0.05). The amount of subcutaneous fat affected the detection rate of the ASA (P < 0.05) but not the AKA. In CT scans of ASA detection, the mean CT values in the aorta at the arch and at T11 were 360 and 358 HU, respectively, whereas in CT scans without ASA detection, the CT values in the aorta at the arch and at T11 were lower (P < 0.05), 297 and 317 HU, respectively.

CONCLUSIONS

The ASA and AKA were less frequently detected in our cohort than previous reports. The visualization of the ASA and AKA was significantly affected by aortic enhancement, the "vertebral mass index", and the contrast-to-noise ratio.