Quantification of carotid plaque volume measurements using 3D ultrasound imaging

A Quantitative Method for the Evaluation of Deep Vein Thrombosis in a Murine Model Using Three-Dimensional Ultrasound Imaging

Deep vein thrombosis (DVT) is a life-threatening condition that can lead to its sequelae pulmonary embolism (PE) or post-thrombotic syndrome (PTS). Murine models of DVT are frequently used in early-stage disease research and to assess potential therapies. This creates the need for the reliable and easy quantification of blood clots. In this paper, we present a novel high-frequency 3D ultrasound approach for the quantitative evaluation of the volume of DVT in an in vitro model and an in vivo murine model. The proposed method involves the use of a high-resolution ultrasound acquisition system and semiautomatic segmentation of the clot. The measured 3D volume of blood clots was validated to be correlated with in vitro blood clot weights with an R2 of 0.89. Additionally, the method was confirmed with an R2 of 0.91 in the in vivo mouse model with a cylindrical volume from macroscopic measurement. We anticipate that the proposed method will be useful in pharmacological or therapeutic studies in murine models of DVT.

Development of a Three-Dimensional Carotid Ultrasound Image Segmentation Workflow for Improved Efficiency, Reproducibility and Accuracy in Measuring Vessel Wall and Plaque Volume and Thickness

Automated segmentation of carotid lumen-intima boundary (LIB) and media-adventitia boundary (MAB) by deep convolutional neural networks (CNN) from three-dimensional ultrasound (3DUS) images has made assessment and monitoring of carotid atherosclerosis more efficient than manual segmentation. However, training of CNN still requires manual segmentation of LIB and MAB. Therefore, there is a need to improve the efficiency of manual segmentation and develop strategies to improve segmentation accuracy by the CNN for serial monitoring of carotid atherosclerosis. One strategy to reduce segmentation time is to increase the interslice distance (ISD) between segmented axial slices of a 3DUS image while maintaining the segmentation reliability. We, for the first time, investigated the effect of ISD on the reproducibility of MAB and LIB segmentations. The intra-observer reproducibility of LIB and MAB segmentations at ISDs of 1 mm and 2 mm was not statistically significantly different, whereas the reproducibility at ISD = 3 mm was statistically lower. Therefore, we conclude that segmentation with an ISD of 2 mm provides sufficient reliability for CNN training. We further proposed training the CNN by the baseline images of the entire cohort of patients for automatic segmentation of the follow-up images acquired for the same cohort. We validated that segmentation with this time-based partitioning approach is more accurate than that produced by patient-based partitioning, especially at the carotid bifurcation. This study forms the basis for an efficient, reproducible, and accurate 3DUS workflow for serial monitoring of carotid atherosclerosis useful in risk stratification of cardiovascular events and in evaluating the efficacy of new treatments.

Feasibility and Accuracy of Measuring Carotid Plaque Volume (Burden) With Contrast-Enhanced Tomographic 3D Ultrasound and Ultrasound Image Fusion

BACKGROUND

Stenosis severity has been the indication for carotid endarterectomy (CEA) for 4 decades, but the annual stroke risk in asymptomatic carotid stenosis >70% is under 2%. Atherosclerotic volume has emerged as a risk factor for future stroke, but needs to be measured noninvasively. Tomographic ultrasound (tUS) is a novel technology that assembles 3D images in seconds. We evaluated accuracy of measuring Carotid Plaque Volume (CPV) with tUS in patients undergoing CEA.

METHOD

Consecutive patients were imaged immediately before CEA by tUS and contrast-enhanced tUS (CEtUS). CPV was measured using tUS, CEtUS, and a fused images incorporating both tUS and CEtUS by trained vascular scientists. Precise volume of the endarterectomy specimen was measured using Archimedes technique.

RESULTS

Mean ± sd (range) CPV in 129 endarterectomy specimens was 0.75 ± 0.43 cm³ (0.10-2.47 cm³). Mean ± sd CPV measured by tUS (n = 114) was 0.87 ± 0.51 cm³, CEtUS (n = 104) was 0.75 ± 0.45 cm³ and with fusion (n = 95) was 0.83 ± 0.49 cm³. Differences between specimen volume and CPV measured by tUS (0.13 ± 0.24 cm³), CEtUS (-0.01 ± 0.21 cm³) or fusion (-0.08 ± 0.20) were clinically insignificant. Intra-/interobserver differences were minimal.

CONCLUSIONS

tUS accurately measures CPV with excellent intra-/interobserver agreement. CEtUS improves accuracy if precise CPV measurement is needed for research but tUS alone would be sufficient for population screening.

Quantification of Local Vessel Wall and Plaque Volume Change for Assessment of Effects of Therapies on Carotid Atherosclerosis Based on 3-D Ultrasound Imaging

We developed a new method to measure the voxel-based vessel-wall-plus-plaque volume (VWV). In addition to quantifying local thickness change as in the previously introduced vessel-wall-plus-plaque thickness (VWT) metric, voxel-based VWV further considers the circumferential change associated with vascular remodeling. Three-dimensional ultrasound images were acquired at baseline and 1 y afterward. The vessel wall region was divided into small voxels with the voxel-based VWV change (ΔVVol%) computed by taking the percentage volume difference between corresponding voxels in the baseline and follow-up images. A 3-D carotid atlas was developed to allow visualization of the local thickness and circumferential change patterns in the pomegranate versus the placebo groups. A new patient-based biomarker was obtained by computing the mean ΔVVol% over the entire 3-D map for each patient (ΔVVol%¯). ΔVVol%¯ detected a significant difference between patients randomized to pomegranate juice/extract and placebo groups (p = 0.0002). The number of patients required by ΔVVol%¯ to establish statistical significance was approximately a third of that required by the local VWT biomarker. The increased sensitivity afforded by the proposed biomarker improves the cost-effectiveness of clinical studies evaluating new anti-atherosclerotic treatments.

Three-dimensional ultrasound virtual organ computer-aided analysis to monitor fetal intracranial volume development characteristics: A multi-center study in a Chinese population

OBJECTIVES

This study aimed to evaluate the feasibility of monitoring fetal intracranial volume using three-dimensional ultrasound virtual organ computer-aided analysis (VOCAL) technology and to analyze normal fetal brain growth.

METHODS

This multi-center prospective cross-sectional study included 821 pregnant women (18-40 gestational weeks) divided into 23 groups according to gestational week. We used transabdominal three-dimensional ultrasound VOCAL to monitor fetal intracranial volume; explore the correlation between intracranial volume and gestational age, biparietal diameter (BPD), and head circumference (HC); and analyze the proportion of brain weight to body weight.

RESULTS

The intracranial volume of normal fetuses conformed to the normal distribution, gradually increased with gestational age, and was highly correlated with gestational age (r = 0.977), BPD (r = 0.975), and HC (r = 0.953; p < 0.001). The median percentage of brain weight (BW) to estimated fetal weight (EFW) was between 13% and 21%, and the BW/EFW ratio showed a significant downward trend in the third trimester. The VOCAL technology monitored the fetal intracranial volume with good repeatability.

CONCLUSIONS

VOCAL technology is feasible for monitoring the fetal intracranial volume, and the intracranial volume increases more than 10-times in the second and third trimesters.

Three-dimensional ultrasound assessment of effects of therapies on carotid atherosclerosis using vessel wall thickness maps

We present a new method for assessing the effects of therapies on atherosclerosis, by measuring the weighted average of carotid vessel-wall-plus-plaque thickness change (ΔVWT¯_Weighted) in 120 patients randomized to pomegranate juice/extract versus placebo. Three-dimensional ultrasound images were acquired at baseline and one year after. Three-dimensional VWT maps were reconstructed and then projected onto a carotid template to obtain two-dimensional VWT maps. Anatomic correspondence on the two-dimensional VWT maps was optimized to reduce misalignment for the same subject and across subjects. A weight was computed at each point on the two-dimensional VWT map to highlight anatomic locations likely to exhibit plaque progression/regression, resulting in ΔVWT¯_Weighted for each subject. The weighted average of VWT-Change measured from the two-dimensional VWT maps with correspondence alignment (ΔVWT¯_Weighted,MDL) detected a significant difference between the pomegranate and placebo groups (P = 0.008). This method improves the cost-effectiveness of proof-of-concept studies involving new therapies for atherosclerosis.

Short-Term Progression of Multiterritorial Subclinical Atherosclerosis

BACKGROUND

Atherosclerosis progression predicts cardiovascular events; however, progression of multiterritorial subclinical atherosclerosis is incompletely understood.

OBJECTIVES

This study sought to study short-term progression of atherosclerosis using different noninvasive imaging techniques and their relationship with cardiovascular risk.

METHODS

The study included 3,514 PESA (Progression of Early Subclinical Atherosclerosis) study participants (45.7 ± 4.2 years of age; 63% men). Participants underwent 2-dimensional vascular ultrasound (2DVUS) of abdominal aorta, carotid, iliac, and femoral territories to determine a plaque number score; 3DVUS to quantify carotid and femoral plaque volume; and coronary artery calcium score (CACS) at baseline and 2.8 years later. The authors calculated the rate of new disease incidence and changes in disease extent. Logistic regression models were used to evaluate associations of progression rates with baseline cardiovascular risk factors and estimated 10-year risk.

RESULTS

Imaging detected short-term (3-year) atherosclerosis progression in 41.5% of participants (26.4% by 2DVUS, 21.3% by 3DVUS, and 11.5% by CACS), particularly in peripheral territories examined by vascular ultrasound. New atherosclerosis onset accounted for approximately one-third of total progression, also more frequently by 2DVUS and 3DVUS (29.1% and 16.6%, respectively), than by CACS (2.9%). Participants with baseline disease by all 3 modalities (n = 432) also showed significant atherosclerosis progression (median: 1 plaque [interquartile range (IQR): -1 to 3 plaques] by 2DVUS; 7.6 mm³ [IQR: -32.2 to 57.6 mm³] by 3DVUS; and 21.6 Agatston units [IQR: 4.8 to 62.6 Agatston units] by CACS). Age, sex, dyslipidemia, hypertension, smoking, and family history of premature cardiovascular disease contributed to progression, with dyslipidemia the strongest modifiable risk factor. Although disease progression correlated with cardiovascular risk, progression was detected in 36.5% of participants categorized as low risk.

CONCLUSIONS

With this multimodal and multiterritorial approach, the authors detected short-term progression of early subclinical atherosclerosis in a substantial proportion (41.5%) of apparently healthy middle-aged men and women, more frequently by peripheral 2D/3DVUS than by CACS. Disease progression, as defined in this study, correlated with almost all cardiovascular risk factors and estimated risk. (Progression of Early Subclinical Atherosclerosis [PESA]; NCT01410318).

Automated 3D geometry segmentation of the healthy and diseased carotid artery in free-hand, probe tracked ultrasound images

PURPOSE

Rupture of an arterosclerotic plaque in the carotid artery is a major cause of stroke. Biomechanical analysis of plaques is under development aiming to aid the clinician in the assessment of plaque vulnerability. Patient-specific three-dimensional (3D) geometry assessment of the carotid artery, including the bifurcation, is required as input for these biomechanical models. This requires a high-resolution, 3D, noninvasive imaging modality such as ultrasound (US). In this study, a high-resolution two-dimensional (2D) linear array in combination with a magnetic probe tracking device and automatic segmentation method was used to assess the geometry of the carotid artery. The advantages of using this system over a 3D ultrasound probe are its higher resolution (spatial and temporal) and its larger field of view.

METHODS

A slow sweep (v = ± 5 mm/s) was made over the subject's neck so that the full geometry of the bifurcated geometry of the carotid artery is captured. An automated segmentation pipeline was developed. First, the Star-Kalman method was used to approximate the center and size of the vessels for every frame. Images were filtered with a Gaussian high-pass filter before conversion into the 2D monogenic signals, and multiscale asymmetry features were extracted from these data, enhancing low lateral wall-lumen contrast. These images, in combination with the initial ellipse contours, were used for an active deformable contour model to segment the vessel lumen. To segment the lumen-plaque boundary, Otsu's automatic thresholding method was used. Distension of the wall due to the change in blood pressure was removed using a filter approach. Finally, the contours were converted into a 3D hexahedral mesh for a patient-specific solid mechanics model of the complete arterial wall.

RESULTS

The method was tested on 19 healthy volunteers and on 3 patients. The results were compared to manual segmentation performed by three experienced observers. Results showed an average Hausdorff distance of 0.86 mm and an average similarity index of 0.91 for the common carotid artery (CCA) and 0.88 for the internal and external carotid artery. For the total algorithm, the success rate was 89%, in 4 out of 38 datasets the ICA and ECA were not sufficient visible in the US images. Accurate 3D hexahedral meshes were successfully generated from the segmented images .

CONCLUSIONS

With this method, a subject-specific biomechanical model can be constructed directly from a hand-held 2D US measurement, within 10 min, with a minimal user input. The performance of the proposed segmentation algorithm is comparable to or better than algorithms previously described in literature. Moreover, the algorithm is able to segment the CCA, ICA, and ECA including the carotid bifurcation in transverse B-mode images in both healthy and diseased arteries.

Three-dimensional ultrasound evaluation of the effects of pomegranate therapy on carotid plaque texture using locality preserving projection

BACKGROUND AND OBJECTIVE

Dietary supplements are expected to confer a smaller beneficial effect than medical treatments. Therefore, there is a need to develop cost-effective biomarkers that can demonstrate the efficacy of such supplements for carotid atherosclerosis. The aim of this study is to develop such a biomarker based on the changes of 376 plaque textural features measured from 3D ultrasound images.

METHODS

Since the number of features (376) was greater than the number of subjects (171) in this study, principal component analysis (PCA) was applied to reduce the dimensionality of feature vectors. To generate a scalar biomarker for each subject, elements in the reduced feature vectors produced by PCA were weighted using locality preserving projections (LPP) to capture essential patterns exhibited locally in the feature space. 96 subjects treated by pomegranate juice and tablets, and 75 subjects receiving placebo-matching juice and tablets were evaluated in this study. The discriminative power of the proposed biomarker was evaluated and compared with existing biomarkers using t-tests. As the cost of a clinical trial is directly related to the number of subjects enrolled, the cost-effectiveness of the proposed biomarker was evaluated by sample size estimation.

RESULTS

The proposed biomarker was more able to discriminate plaque changes exhibited by the pomegranate and placebo groups than total plaque volume (TPV) according to the result of t-tests (TPV: p=0.34, Proposed biomarker: p=1.5×10^-5). The sample size required by the new biomarker to detect a significant effect was 20 times smaller than that required by TPV.

CONCLUSION

With the increase in cost-effectiveness afforded by the proposed biomarker, more proof-of-principle studies for novel treatment options could be performed.

Fractal dimension based carotid plaque characterization from three-dimensional ultrasound images

Irregularity of the plaque surface associated with previous plaque rupture plays an important role in the risk estimation of stroke caused by carotid atherosclerotic lesions. Thus, the aim of this study is to develop and validate novel vulnerability biomarkers from three-dimensional ultrasound (3DUS) images by analyzing the surface morphological characteristics of carotid plaque using fractal geometry features. In the experiments, a total of 38 3DUS plaque images were obtained from two groups of patients treated with 80 mg of atorvastatin or placebo daily for 3 months respectively. Two types of 3D fractal dimensions (FDs) were used to describe the smoothness of plaque surface morphology and the roughness from intensity of 3DUS images. Student's t test showed that the two fractal features were effective for detecting the statin-related changes in carotid atherosclerosis with p < 0.00023 and p < 0.0113 respectively. It was concluded that the 3D FD measurements were effective for analyzing carotid plaque characteristics and especially effective for evaluating the impact of atorvastatin treatment. Graphical abstract ᅟ.

Inter-Scan Reproducibility of Carotid Plaque Volume Measurements by 3-D Ultrasound

We tested a novel 3-D matrix transducer with respect to inter-scan reproducibility of carotid maximum plaque thickness (MPT) and volume measurements. To improve reproducibility while focusing on the largest plaque/most diseased part of the carotid artery, we introduced a new partial plaque volume (PPV) measure centered on MPT. Total plaque volume (TPV), PPV from a 10-mm segment and MPT were measured using dedicated semi-automated software on 38 plaques from 26 patients. Inter-scan reproducibility was assessed using the t-test, Bland-Altman plots and Pearson's correlation coefficient. There was a mean difference of 0.01 mm in MPT (limits of agreement: -0.45 to 0.42 mm, Pearson's correlation coefficient: 0.96). Both volume measurements exhibited high reproducibility, with PPV being superior (limits of agreement: -35.3 mm³ to 33.5 mm³, Pearson's correlation coefficient: 0.96) to TPV (limits of agreement: -88.2 to 61.5 mm³, Pearson's correlation coefficient: 0.91). The good reproducibility revealed by the present results encourages future studies on establishing plaque quantification as part of cardiovascular risk assessment and for follow-up of disease progression over time.

Carotid plaque volume in patients undergoing carotid endarterectomy

BACKGROUND

The main indication for carotid endarterectomy (CEA) is severity of carotid artery stenosis, even though most strokes in carotid disease are embolic. The relationship between carotid plaque volume (CPV) and symptoms of cerebral ischaemia, and the measurement of CPV by minimally invasive tomographic ultrasound imaging, were investigated.

METHODS

The volume of the endarterectomy specimen was measured using a validated saline suspension technique in patients undergoing CEA. Time from last symptom and severity of stenosis measured by duplex ultrasonography were recorded. Middle cerebral artery emboli were counted using transcranial Doppler imaging (TCD) in a subset of patients.

RESULTS

Some 339 patients were included, 270 with symptomatic and 69 with asymptomatic carotid stenosis. Mean(s.d.) CPV was higher in symptomatic than in asymptomatic patients (0·97(0·43) versus 0.74(0·41) cm³ ; P < 0·001). CPV did not correlate with severity of carotid stenosis (P = 0·770). Mean CPV was highest at 1·03(0·46) cm³ in the 4 weeks following cerebral symptoms, declining to 0·78(0·36) cm³ beyond 8 weeks. Among 33 patients who had TCD, mean CPV was 1·00(0·48) cm³ in the 27 patients with ipsilateral cerebral emboli compared with 0·67(0·16) cm³ in those without (P = 0·142). There was excellent correlation between CPV measured by tomographic ultrasound imaging and the endarterectomy specimen in 34 patients (r = 0·93, P < 0·001).

CONCLUSION

CPV correlated with symptoms of cerebral ischaemia, but not carotid stenosis. It could be a potential indicator for CEA.

Three-Dimensional Echographic Evaluation of Carotid Artery Disease

The introduction of three-dimensional echography (3D echo) in vascular field is not recent, but it still remains a seldom-used technique because of the costs of ultrasound probe and the need of dedicated laboratories. Therefore, despite significant prognostic implications, the high diagnostic accuracy in plaque definition, and the relative ease of use, 3D echo in vascular field is a niche technique. The purpose of this review is mainly clinical and intends to demonstrate the potential strength of a 3D approach, including technical aspects, in order to present to clinicians and imagers the appealing aspects of a noninvasive and radiation-free methodology with relevant diagnostic and prognostic correlates in the assessment of carotid atherosclerosis. A comprehensive literature search (since 1990s to date) using the PubMed, MEDLINE, and Cochrane libraries databases has been conducted. Articles written in English have been assessed, including reviews, clinical trials, meta-analyses, and interventional/observational studies. Manual cross-referencing was also performed, and relevant references from selected articles were reviewed. The search was limited to studies conducted in humans. Search terms, retrieved also with PubMed Advanced search and AND/OR Boolean operators (mainly in title and abstract), included three-dimensional, echo, stroke/transient ischemic attack, predictors, carotid, imaging, and biomarkers.

Freehand 3-D Ultrasound Imaging: A Systematic Review

Two-dimensional ultrasound (US) imaging has been successfully used in clinical applications as a low-cost, portable and non-invasive image modality for more than three decades. Recent advances in computer science and technology illustrate the promise of the 3-D US modality as a medical imaging technique that is comparable to other prevalent modalities and that overcomes certain drawbacks of 2-D US. This systematic review covers freehand 3-D US imaging between 1970 and 2017, highlighting the current trends in research fields, the research methods, the main limitations, the leading researchers, standard assessment criteria and clinical applications. Freehand 3-D US systems are more prevalent in the academic environment, whereas in clinical applications and industrial research, most studies have focused on 3-D US transducers and improvement of hardware performance. This topic is still an interesting active area for researchers, and there remain many unsolved problems to be addressed.

Sensitive three-dimensional ultrasound assessment of carotid atherosclerosis by weighted average of local vessel wall and plaque thickness change

PURPOSE

Vitamin B deficiency has been identified as a risk factor for vascular events. However, the reduction of vascular events was not shown in large randomized controlled trials evaluating B-Vitamin therapy. There is an important requirement to develop sensitive biomarkers to be used as efficacy targets for B-Vitamin therapy as well as other dietary treatments and lifestyle regimes that are being developed. Carotid vessel-wall-plus-plaque thickness change (VWT-Change) measured from 3D ultrasound has been shown to be sensitive to atorvastatin therapies in previous studies. However, B-Vitamin treatment is expected to confer a smaller beneficial effect in carotid atherosclerosis than the strong dose of atorvastatin. This paper introduces a sensitive atherosclerosis biomarker based on the weighted mean VWT-Change measurement from 3D ultrasound with a purpose to detect statistically significant effect of B-Vitamin therapy.

METHODS

Of the 56 subjects analyzed in this study, 27 were randomized to receive a B-Vitamin tablet daily and 29 received a placebo tablet daily. Participants were scanned at baseline and 1.9 ± 0.8 yr later. The 3D VWT map at each scanning session was computed by matching the outer wall and lumen surfaces on a point-by-point basis. The 3D annual VWT-Change maps were obtained by first registering the 3D VWT maps obtained at the baseline and follow-up scanning sessions, and then taking the point-wise difference in VWT and dividing the result by the years elapsed from the baseline to the follow-up scanning session. The 3D VWT-Change maps constructed for all patients were mapped to a 2D carotid template to adjust for the anatomic variability of the arteries. A weight at each point of the carotid template was assigned based on the degree of correlation between the VWT-Change measurements exhibited at that point and the treatment received (i.e., B-Vitamin or placebo) quantified by mutual information. The weighted mean of VWT-Change for each patient, denoted by ΔVWT¯Weighted, was computed according to this weight. T-tests were performed to compare the sensitivity of ΔVWT¯Weighted with existing biomarkers in detecting treatment effects. These biomarkers included changes in intima-media thickness (IMT), total plaque area (TPA), vessel wall volume (VWV), unweighted average of VWT-Change (ΔVWT¯) and a previously described biomarker, denoted by ΔVWT¯S, that quantifies the mean VWT-Change specific to regions of interest identified by a feature selection algorithm.

RESULTS

Among the six biomarkers evaluated, the effect of B Vitamins was detected only by ΔVWT¯Weighted in this cohort (P=4.4×10-3). The sample sizes per treatment group required to detect an effect as large as exhibited in this study were 139, 178, 41 for ΔVWV, ΔVWT¯ and ΔVWT¯Weighted respectively.

CONCLUSION

The proposed weighted mean of VWT-Change is more sensitive than existing biomarkers in detecting treatment effects. This measurement tool will allow for many proof-of-principal studies to be performed for various novel treatments before a more costly study involving a larger population is held to validate the results.

Semiautomatic quantification of carotid plaque volume with three-dimensional ultrasound imaging

OBJECTIVE

Vessel wall volume (VWV) assessed by three-dimensional duplex ultrasound (3DUS) imaging provides a more comprehensive measure of plaque burden than conventional two-dimensional measures of diameter stenosis. We previously demonstrated that manual outlining of the arterial lumen-intima boundary and outer wall boundary can be performed reliably on images obtained with a commercially available 3D-DUS transducer. Manual segmentation, however, is time consuming (∼45 minutes), limiting its clinical translation. We have developed a semiautomatic algorithm (manual selection of the carotid bifurcation image with subsequent automatic plaque outlining) to outline carotid plaques on 3DUS data sets. In this study, we investigated the accuracy, reproducibility, reliability, and time taken by this algorithm.

METHODS

3DUS data sets from 30 patients with asymptomatic ≥50% carotid stenosis underwent manual outlining of lumen-intima boundary and outer wall boundary to measure VWV. Two observers implemented a semiautomatic segmentation algorithm. The algorithm's accuracy was compared with manual outlining using the Pearson correlation coefficient. The Dice similarity coefficient (DSC) and modified-Hausdorff distance (MHD) were used to quantify the geometric similarity of the outlines. We also compared results after an intermediate stage of the algorithm vs the complete algorithm. Reproducibility and the least amount of detectable change in plaque volume were computed for each method. Intraobserver and interobserver metrics for each method were computed using the intraclass correlation coefficient (ICC), coefficient of variability (CV), minimum detectable change (MDC), and standard error of measurement (SEM) of the VWV.

RESULTS

Plaque volume estimates obtained from the semiautomatic algorithm were accurate compared with manual outlining. The Pearson correlation coefficient was 0.76 (P < .001), and measurements were geometrically similar (DSC, 0.85; MHD, 0.48 mm). The algorithm was more reproducible and reliable and could detect smaller changes in plaque volume on repeat imaging (low interobserver variability: ICC, 0.9; CV, 8.22%; MDC, 5.57%; SEM, 1.45%; DSC, 0.88; MHD, 0.43 mm). Intraobserver variability was even lower (ICC, 0.9; CV, 8%; MDC, 3.62%; SEM, 1.31%; DSC, 0.89; MHD, 0.37 mm). Plaque volume estimates at the intermediate stage of the algorithm matched results from the full algorithm (Pearson correlation coefficient, 0.76; DSC, 0.84; MHD, 0.52 mm). The intermediate approach, however, was less reliable than the full algorithm (interobserver: ICC, 0.81; CV, 11.7%; MDC, 9.58%; SEM, 3.46%; DSC, 0.88; MHD, 0.42 mm; intraobserver: ICC, 0.87; CV, 8.6%; MDC, 4.55%; SEM, 1.64%; DSC, 0.89; MHD, 0.38 mm). The full algorithm required ∼14 minutes to implement. However, a quick (7 minutes) and accurate assessment of VWV can be obtained by running only the intermediate stage of the algorithm, although with a loss in repeatability and reliability.

CONCLUSIONS

We present a unique algorithm to perform semiautomatic quantification of carotid plaque volume using 3DUS imaging. It is quick (mean time, 14 minutes), accurate, repeatable, and implementable in a clinical environment and in longitudinal studies tracking plaque progression. It reliably detects plaque volume changes as low as 4% to 6% with 95% confidence.

Three-Dimensional Ultrasound of Carotid Plaque

Measurement of plaque burden is different from measurement of carotid intima-media thickness (IMT). Carotid total plaque area is a stronger predictor of cardiovascular risk than IMT, and in contrast to progression of IMT, which does not predict cardiovascular events, progression of total plaque area and total plaque volume strongly predict cardiovascular events. Measurement of plaque burden is useful in genetic research, and in evaluation of new therapies for atherosclerosis. Perhaps more importantly, it can be used for management of patients. A strategy called "treating arteries instead of treating risk factors" markedly reduces risk among patients with asymptomatic carotid stenosis.

Secondary Stroke Prevention: Improving Diagnosis and Management with Newer Technologies

Treatment of hypertension, diabetes, high cholesterol, smoking cessation, and healthy lifestyle have all contributed to the decline in the incidence of vascular disease over the last several decades. Patients who suffer an acute stroke are at a high risk for recurrence. Introduction of newer technologies and their wider use allows for better identification of patients in whom the risk of recurrence following an acute stroke may be very high. Traditionally, the major focus for diagnosis and management has focused on patient history, examination, imaging for carotid stenosis/occlusion, and detection of AF and paroxysmal AF (PAF) with 24-48 h cardiac monitoring. This review focuses on the usefulness of three newer investigative tools that are becoming widely available and lead to better prevention. Continuous ambulatory blood pressure measurements for 24 h or longer and 3D Doppler measures of the carotid arteries provide key useful information on the state of vascular health and enhance our ability to monitor the response to preventive therapies. Furthermore, the detection of PAF can be significantly improved with prolonged cardiac monitoring for 3 weeks or longer, enabling the initiation of appropriate prevention therapy. This review will focus on the potential impact and importance of these emerging technologies on the prevention of recurrent stroke in high-risk patients.

Comparison of 3D ultrasound and magnetic resonance imaging for microwave ablation in the canine splenomegaly model

PURPOSE

Microwave ablation is used for the treatment of hypersplenism. Image guidance and ablation volume assessment is important to ensure that the ablation is successful. The accuracy of 3D ultrasound (US) and magnetic resonance imaging (MRI) in determining the parameters for microwave ablation were compared in a canine splenomegaly model.

METHODS

Microwave ablation of the spleen was performed on 13 dogs with congestive splenomegaly. Several combinations of power output and ablation time were used: 60 W for 300 s, 50 W for 360 s and 40 W for 450 s. The ablation zone volume was measured by 3D US and 3D MRI immediately after microwave ablation, and at 1, 2 and 8 weeks thereafter.

RESULTS

Compared with 3D MRI, the ablation zone reconstruction rate was lower with 3D US (92 vs. 100%). However, there was no significant difference was found in the ablation volume calculated soon after the treatment and 1 week and 2 months later.

CONCLUSION

3D US may be useful for quantifying the volume of microwave ablation zones in the spleens of experimental animals and appears promising as an alterative modality to MRI for clinical examinations.

Reproducibility of two 3-D ultrasound carotid plaque quantification methods

Compared with single 2-D images, emerging 3-D ultrasound technologies hold the promise of reducing variability and increasing sensitivity in the quantification of carotid plaques for individual cardiovascular risk stratification. Inter- and intra-observer agreement between a manual, cross-sectional, 2-D freehand sweep and a mechanical 3-D ultrasound investigation of 62 carotid artery plaques is reported with intra-class correlation coefficients (with 95% confidence intervals). Inter-observer agreement was 0.60 (0.29-0.77) for the freehand method and 0.89 (0.83-0.93) for the mechanical 3-D acquisition. The use of semi-automated computerized planimetric measurements of plaque burden has high intra-observer repeatability, but is vulnerable to systematic inter-observer differences. For the 2-D freehand sweep, a considerable contribution to variation is introduced by the scanning procedure itself, that is, the lack of controlled motion along the third dimension. Future implementation of 3-D ultrasound quantification in large-scale studies of inter-individual cardiovascular risk assessment seems justified using the methods described.

A 3-D ultrasound imaging robotic system to detect and quantify lower limb arterial stenoses: in vivo feasibility

The degree of stenosis is the most common criterion used to assess the severity of lower limb peripheral arterial disease. Two-dimensional ultrasound (US) imaging is the first-line diagnostic method for investigating lesions, but it cannot render a 3-D map of the entire lower limb vascular tree required for therapy planning. We propose a prototype 3-D US imaging robotic system that can potentially reconstruct arteries from the iliac in the lower abdomen down to the popliteal behind the knee. A realistic multi-modal vascular phantom was first conceptualized to evaluate the system's performance. Geometric accuracies were assessed in surface reconstruction and cross-sectional area in comparison to computed tomography angiography (CTA). A mean surface map error of 0.55 mm was recorded for 3-D US vessel representations, and cross-sectional lumen areas were congruent with CTA geometry. In the phantom study, stenotic lesions were properly localized and severe stenoses up to 98.3% were evaluated with -3.6 to 11.8% errors. The feasibility of the in vivo system in reconstructing the normal femoral artery segment of a volunteer and detecting stenoses on a femoral segment of a patient was also investigated and compared with that of CTA. Together, these results encourage future developments to increase the robot's potential to adequately represent lower limb vessels and clinically evaluate stenotic lesions for therapy planning and recurrent non-invasive and non-ionizing follow-up examinations.

The relationship of carotid three-dimensional ultrasound vessel wall volume with age and sex: comparison to carotid intima-media thickness

The relationship of three-dimensional ultrasound (3DUS)-derived carotid vessel wall volume (VWV) was evaluated with respect to age and sex. B-mode and 3DUS images were acquired for 316 subjects from diverse groups including obese primary prevention, diabetic nephropathy, renal transplant and rheumatoid arthritis populations. The relationship for intima-media thickness (IMT) and VWV with age and sex were determined using Pearson-product-moment correlations. Mean IMT (r = 0.18, p = 0.001) and VWV (r = 0.24, p < 0.01) correlated modestly with age. There were modest correlations in males (IMT, r = 0.19, p = 0.003; VWV, r = 0.34, p < 0.001) and in females for IMT and age (r = 0.30, p = 0.007) but not between 3DUS VWV and age in females (r = 0.10, p = 0.4). Significant associations between plaque and VWV (r = 0.36, p = 0.001) but not IMT suggest different correlations in females that may be attributed to plaque.

Novel methodology for 3D reconstruction of carotid arteries and plaque characterization based upon magnetic resonance imaging carotid angiography data

In this study, we present a novel methodology that allows reliable segmentation of the magnetic resonance images (MRIs) for accurate fully automated three-dimensional (3D) reconstruction of the carotid arteries and semiautomated characterization of plaque type. Our approach uses active contours to detect the luminal borders in the time-of-flight images and the outer vessel wall borders in the T(1)-weighted images. The methodology incorporates the connecting components theory for the automated identification of the bifurcation region and a knowledge-based algorithm for the accurate characterization of the plaque components. The proposed segmentation method was validated in randomly selected MRI frames analyzed offline by two expert observers. The interobserver variability of the method for the lumen and outer vessel wall was -1.60%±6.70% and 0.56%±6.28%, respectively, while the Williams Index for all metrics was close to unity. The methodology implemented to identify the composition of the plaque was also validated in 591 images acquired from 24 patients. The obtained Cohen's k was 0.68 (0.60-0.76) for lipid plaques, while the time needed to process an MRI sequence for 3D reconstruction was only 30 s. The obtained results indicate that the proposed methodology allows reliable and automated detection of the luminal and vessel wall borders and fast and accurate characterization of plaque type in carotid MRI sequences. These features render the currently presented methodology a useful tool in the clinical and research arena.

Hyperpolarized 3He magnetic resonance functional imaging semiautomated segmentation

RATIONALE AND OBJECTIVES

To improve intra- and interobserver variability and enable the use of functional magnetic resonance imaging (MRI) for multicenter, multiobserver studies, we generated a semiautomated segmentation method for hyperpolarized helium-3 ((3)He) MRI. Therefore the objective of this study was to compare the reproducibility and spatial agreement of manual and semiautomated segmentation of (3)He MRI ventilation defect volume (VDV) and ventilation volume (VV) in subjects with asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF).

MATERIALS AND METHODS

The multistep semiautomated segmentation method we developed employed hierarchical K-means clustering to classify (3)He MRI pixel intensity values into five user-determined clusters ranging from signal void to hyperintense. A seeded region-growing algorithm was also used to segment the (1)H MRI thoracic cavity for coregistration to the (3)He cluster-map, generating VDV and VV.

RESULTS

We compared manual segmentation performed by an expert observer and semiautomated measurements of (3)He MRI VDV and observed strong significant correlations between the volumes generated using each method (asthma, n = 5, r = 0.89, P < .0001; COPD, n = 5, r = 0.84, P < .0001; CF, n = 5, r = 0.89, P < .0001). Semiautomated VDV had high interobserver reproducibility (coefficient of variation [CV] = 7%, intraclass correlation coefficient [ICC] = 0.96); intraobserver reproducibility was significantly higher for semiautomated (CV = 5%, ICC = 1.00) compared to manual VDV (CV = 12%, ICC = 0.98). Spatial agreement for VV determined using the Dice coefficient (D) was also high for all disease states (asthma, D = 0.95; COPD, D = 0.88; CF, D = 0.90).

CONCLUSIONS

Semiautomated segmentation (3)He MRI provides excellent inter- and intraobserver precision with high spatial and quantitative agreement with manual measurements enabling its use in longitudinal studies.

Pulmonary tumor measurements from x-ray computed tomography in one, two, and three dimensions

RATIONALE AND OBJECTIVES

We evaluated the accuracy and reproducibility of three-dimensional (3D) measurements of lung phantoms and patient tumors from x-ray computed tomography (CT) and compared these to one-dimensional (1D) and two-dimensional (2D) measurements.

MATERIALS AND METHODS

CT images of three spherical and three irregularly shaped tumor phantoms were evaluated by three observers who performed five repeated measurements. Additionally, three observers manually segmented 29 patient lung tumors five times each. Follow-up imaging was performed for 23 tumors and response criteria were compared. For a single subject, imaging was performed on nine occasions over 2 years to evaluate multidimensional tumor response. To evaluate measurement accuracy, we compared imaging measurements to ground truth using analysis of variance. For estimates of precision, intraobserver and interobserver coefficients of variation and intraclass correlations (ICC) were used. Linear regression and Pearson correlations were used to evaluate agreement and tumor response was descriptively compared.

RESULTS

For spherical shaped phantoms, all measurements were highly accurate, but for irregularly shaped phantoms, only 3D measurements were in high agreement with ground truth measurements. All phantom and patient measurements showed high intra- and interobserver reproducibility (ICC >0.900). Over a 2-year period for a single patient, there was disagreement between tumor response classifications based on 3D measurements and those generated using 1D and 2D measurements.

CONCLUSION

Tumor volume measurements were highly reproducible and accurate for irregular, spherical phantoms and patient tumors with nonuniform dimensions. Response classifications obtained from multidimensional measurements suggest that 3D measurements provide higher sensitivity to tumor response.

Three-dimensional ultrasound scanning

The past two decades have witnessed developments of new imaging techniques that provide three-dimensional images about the interior of the human body in a manner never before available. Ultrasound (US) imaging is an important cost-effective technique used routinely in the management of a number of diseases. However, two-dimensional viewing of three-dimensional anatomy, using conventional two-dimensional US, limits our ability to quantify and visualize the anatomy and guide therapy, because multiple two-dimensional images must be integrated mentally. This practice is inefficient, and may lead to variability and incorrect diagnoses. Investigators and companies have addressed these limitations by developing three-dimensional US techniques. Thus, in this paper, we review the various techniques that are in current use in three-dimensional US imaging systems, with a particular emphasis placed on the geometric accuracy of the generation of three-dimensional images. The principles involved in three-dimensional US imaging are then illustrated with a diagnostic and an interventional application: (i) three-dimensional carotid US imaging for quantification and monitoring of carotid atherosclerosis and (ii) three-dimensional US-guided prostate biopsy.

Texture analysis of carotid artery atherosclerosis from three-dimensional ultrasound images

PURPOSE

To quantitatively evaluate local carotid arterial statin effects in 3D US images using multiclassifier image texture analysis tools.

METHODS

Texture analysis tools were used to evaluate the effect of 80 mg atorvastatin administered daily to patients with carotid stenosis compared to those treated with placebo. Using three-dimensional carotid ultrasound images, 270 texture features from seven texture techniques were extracted from manually segmented carotid arteries based on the intima-media boundary [vessel wall (VW)]. Individual texture features were compared to the previously determined changes in VW volume (VWV) using the distance between classes, the Wilcoxon rank sum test, and accuracy of the classifiers. Texture features that resulted in maximal classification accuracy from each texture technique were selected using Pudil's sequential floating forward selection (SFFS) as a method of ranking each technique. Finally, SFFS-selected texture features from all texture techniques were used in combination with 24 classifier fusion techniques to improve classification accuracy.

RESULTS

Using the measurement of change in VWV, the distance between classes (DBC), Wilcoxon rank sum (WRS) p-value, and median accuracy measures (ACC) were 0.3798, 0.076, and 54.50%, respectively. Texture features improved the detection of statin-related changes using DBC to 0.5199, using WRS to 0.002, and ACC to 63.87%, respectively. The texture techniques that most differentiated between atorvastatin and placebo classes were Fourier power spectrum and Laws texture energy measures. The average classification accuracy between atorvastatin and placebo classes was improved from 57.22 +/- 12.11% using VWV to 97.87 +/- 3.93% using specific texture features. Furthermore, the use of specific texture features resulted in the average area under the receiver-operator characteristic curve (AUC) a value of 0.9988 +/- 0.0069 compared to 0.617 +/- 0.15 using carotid VWV.

CONCLUSIONS

Based on DBC, WRS, ACC, and AUC texture features derived from 3D carotid ultrasound were observed to be more sensitive in detecting statin-related changes in carotid atherosclerosis than VWV suggesting that texture classifiers can be used to detect changes in carotid atherosclerosis after therapy.

Three-dimensional ultrasound imaging

This review is about the development of three-dimensional (3D) ultrasonic medical imaging, how it works, and where its future lies. It assumes knowledge of two-dimensional (2D) ultrasound, which is covered elsewhere in this issue. The three main ways in which 3D ultrasound may be acquired are described: the mechanically swept 3D probe, the 2D transducer array that can acquire intrinsically 3D data, and the freehand 3D ultrasound. This provides an appreciation of the constraints implicit in each of these approaches together with their strengths and weaknesses. Then some of the techniques that are used for processing the 3D data and the way this can lead to information of clinical value are discussed. A table is provided to show the range of clinical applications reported in the literature. Finally, the discussion relating to the technology and its clinical applications to explain why 3D ultrasound has been relatively slow to be adopted in routine clinics is drawn together and the issues that will govern its development in the future explored.

Three-dimensional carotid ultrasound segmentation variability dependence on signal difference and boundary orientation

Quantitative measurements of the progression (or regression) of carotid plaque burden are important in monitoring patients and evaluating new treatment options. We previously developed a quantitative metric to analyze changes in carotid plaque morphology from 3-D ultrasound (US) on a point-by-point basis. This method requires multiple segmentations of the arterial wall and lumen boundaries to obtain the local standard deviation (SD) of vessel-wall-plus-plaque thickness (VWT) so that t-tests could be used to determine whether a change in VWT is statistically significant. However, the requirement for multiple segmentations makes clinical trials laborious and time-consuming. Therefore, this study was designed to establish the relationship between local segmentation SD and local signal difference on the arterial wall and lumen boundaries. We propose metrics to quantify segmentation SD and signal difference on a point-by-point basis, and studied whether the signal difference at arterial wall or lumen boundaries could be used to predict local segmentation SD. The ability to predict the local segmentation SD could eliminate the need of repeated segmentations of a 2-D transverse image to obtain the local segmentation standard deviation, thereby making clinical trials less laborious and saving time. Six subjects involved in this study were associated with different degrees of atherosclerosis: three carotid stenosis subjects with mean plaque area >3 cm(2) and >60% carotid stenosis were involved in a clinical study evaluating the effect of atorvastatin, a cholesterol-lowering and plaque-stabilizing drug; and three subjects with carotid plaque area >0.5 cm(2) were subjects with moderate atherosclerosis. Our results suggest that when local signal difference is higher than 8 greyscale value (GSV), the local segmentation SD stabilizes at 0.05 mm and is thus predictable. This information provides a target value of local signal difference on the arterial boundaries that should be achieved to obtain an accurate prediction of local segmentation SD. (E-mail: bcychiu@alumni.uwo.ca).

Computer-assisted venous thrombosis volume quantification

Venous thrombosis (VT) volume assessment, by verifying its risk of progression when anticoagulant or thrombolytic therapies are prescribed, is often necessary to screen life-threatening complications. Commonly, VT volume estimation is done by manual delineation of few contours in the ultrasound (US) image sequence, assuming that the VT has a regular shape and constant radius, thus producing significant errors. This paper presents and evaluates a comprehensive functional approach based on the combination of robust anisotropic diffusion and deformable contours to calculate VT volume in a more accurate manner when applied to freehand 2-D US image sequences. Robust anisotropic filtering reduces image speckle noise without generating incoherent edge discontinuities. Prior knowledge of the VT shape allows initializing the deformable contour, which is then guided by the noise-filtering outcome. Segmented contours are subsequently used to calculate VT volume. The proposed approach is integrated into a system prototype compatible with existing clinical US machines that additionally tracks the acquired images 3-D position and provides a dense Delaunay triangulation required for volume calculation. A predefined robust anisotropic diffusion and deformable contour parameter set enhances the system usability. Experimental results pertinence is assessed by comparison with manual and tetrahedron-based volume computations, using images acquired by two medical experts of eight plastic phantoms and eight in vitro VTs, whose independently measured volume is the reference ground truth. Results show a mean difference between 16 and 35 mm(3) for volumes that vary from 655 to 2826 mm(3). Two in vivo VT volumes are also calculated to illustrate how this approach could be applied in clinical conditions when the real value is unknown. Comparative results for the two experts differ from 1.2% to 10.08% of the smallest estimated value when the image acquisition cadences are similar.

Longitudinal ultrasound evaluation of carotid atherosclerosis in one, two and three dimensions

The aim of this study was to compare the sensitivity of three ultrasound phenotypes of carotid atherosclerosis in a longitudinal study of patients with diabetic nephropathy. B-mode ultrasound-derived intima-media thickness (IMT), total plaque area (TPA) as well as three-dimensional ultrasound (3DUS) vessel wall volume (VWV) of the common carotid artery (CCA) (VWV(CCA)) and internal carotid artery (ICA). (VWV(CCA+ICA)) were all evaluated in subjects enrolled in a randomized placebo-controlled double blind study of vitamin B therapy. Of 106 subjects randomized, 77 subjects were scanned at baseline and 2.3 +/- 1 y later (range: 0.5 to 4.5 y); of these subjects, 71 had images of sufficient quality for complete analysis of all three measurements. Subjects were analyzed according to the two treatment groups (A and B) and the analysis was performed blinded to treatment group description to prevent any potential for bias in future analyses. There were differences in sensitivity to longitudinal changes observed in all the ultrasound measurements. Specifically, there was no difference in IMT change between treatment groups (0.02 +/- 0.07 mm/y and 0.02 +/- 0.1 mm/y p = 0.15, group A and B, respectively, rates not different from zero [p > 0.05]) or TPA rate between treatment groups (0.09 +/- 0.2 cm(2)/y, significantly different from 0, p = 0.013 and -0.02 +/- 0.3 cm(2)/y in group A and B, respectively). However, the VWV(CCA+ICA) rate of change was significantly greater than 0 for group B (53 +/- 110 mm(3)/y) (p = 0.008), which was significantly (p = 0.034) higher than the rate of change of VWV(CCA+ICA) (nonsignificant, p = 0.6) for group A (-12 +/- 137 mm(3)/y). The relationship between DeltaVWV and DeltaIMT was significant, such that in group A, DeltaVWV(CCA) was positively associated with DeltaIMT (r = 0.44, p < 0.05), and in group B, DeltaVWV(CCA) was negatively correlated with DeltaIMT (r = -0.44, p < 0.01). These results suggest that 3DUS-derived VWV provides necessary and sufficient sensitivity and specificity to measure longitudinal changes in small numbers of carotid atherosclerosis patients at risk of disease progression and over short periods of time.

Scan-rescan and intra-observer variability of magnetic resonance imaging of carotid atherosclerosis at 1.5 T and 3.0 T

Carotid atherosclerosis measurements for eight subjects at baseline and 14 +/- 2 days later were examined using 1.5 T and 3.0 T magnetic resonance imaging (MRI). A single observer blinded to field strength, subject and timepoint manually segmented carotid artery wall and lumen boundaries in randomized images in five measurement trials. Mean increases in the signal-to-noise ratios (SNR) for T1-weighted images acquired at 3.0 T compared to 1.5 T were 90% (scan) and 80% (rescan). Despite significantly improved SNR and contrast-to-noise ratios (CNR) for images acquired at 3.0 T, vessel wall volume (VWV) intra-observer variability was not significantly different using coefficients of variation (COV), and intraclass correlation coefficients (ICC). VWV interscan variability and consistency at both field strengths were not statistically different (1.5 T/3.0 T COV = 5.7%/7.8%, R(2) = 0.96 for 1.5 T and R(2) = 0.87 for 3.0 T). A two-way analysis of variance showed a VWV dependence on field strength but not scan timepoint. In addition, a paired t-test showed significant differences in VWV measured at 3.0 T as compared to 1.5 T. These results suggest that although images acquired at 1.5 T have lower SNR and CNR VWV, measurement variability was not significantly different from 3.0 T VWV and that VWV is field-strength dependent which may be an important consideration for longitudinal studies.

Quantification of carotid vessel wall and plaque thickness change using 3D ultrasound images

Quantitative measurements of carotid plaque burden progression or regression are important in monitoring patients and in evaluation of new treatment options. 3D ultrasound (US) has been used to monitor the progression or regression of carotid artery plaques. This paper reports on the development and application of a method used to analyze changes in carotid plaque morphology from 3D US. The technique used is evaluated using manual segmentations of the arterial wall and lumen from 3D US images acquired in two imaging sessions. To reduce the effect of segmentation variability, segmentation was performed five times each for the wall and lumen. The mean wall and lumen surfaces, computed from this set of five segmentations, were matched on a point-by-point basis, and the distance between each pair of corresponding points served as an estimate of the combined thickness of the plaque, intima, and media (vessel-wall-plus-plaque thickness or VWT). The VWT maps associated with the first and the second US images were compared and the differences of VWT were obtained at each vertex. The 3D VWT and VWT-Change maps may provide important information for evaluating the location of plaque progression in relation to the localized disturbances of flow pattern, such as oscillatory shear, and regression in response to medical treatments.

Measurement of intima-media thickness vs. carotid plaque: uses in patient care, genetic research and evaluation of new therapies

Intima-media thickness (IMT) has been measured for over 20 years, and is widely regarded as a surrogate for atherosclerosis. However, in the carotid arteries atherosclerosis is focal, manifesting as plaques. IMT is often measured deliberately where no plaque exists, or multiple measurements may be averaged, including only one or two that intersect plaque. IMT and plaque are biologically and genetically distinct, so they can be expected to respond differentially to therapies for atherosclerosis. Furthermore, because plaques grow along the carotid arteries 2.4 times faster than they thicken, progression or regression of total plaque area is more sensitive to effects of therapy than IMT. Because plaques also grow and regress circumferentially, three-dimensional (3-D) plaque volume is two orders of magnitude more sensitive to effects of therapy than is IMT. While 3-D ultrasound requires special equipment, total plaque area can be measured using the same equipment as IMT. Because plaque and IMT are biologically and genetically distinct entities, representing different phenotypes of atherosclerosis, both should be measured in any situation where IMT is measured, with the exception of studies in children too young for the occurrence of plaque. IMT should not be called 'atherosclerosis': the phenotype being assessed should be specified.

Hyperpolarized 3He magnetic resonance imaging of chronic obstructive pulmonary disease: reproducibility at 3.0 tesla

RATIONALE AND OBJECTIVES

We assessed subjects with stage II and stage III chronic obstructive pulmonary disease (COPD) and age-matched healthy volunteers at a single center using (3)He magnetic resonance imaging (MRI) at 3.0 T. Measurements of the (3)He apparent diffusion coefficient (ADC) and center coronal slice (3)He ventilation defect volume (VDV) were examined for same-day and 7-day reproducibility as well as subgroup comparisons.

MATERIALS AND METHODS

Twenty-four subjects who provided written informed consent (15 males; mean age 67 +/-7 years) with stage II (n = 9), stage III COPD (n = 7), and age-matched healthy volunteers (n = 8) were enrolled based on their age and pulmonary function test results. All subjects underwent plethysmography, spirometry, and MRI at 3.0 T. The time frame between scans was 7 +/- 2 minutes (same-day rescan) and again 7 +/- 2 days later (7-day rescan). (3)He ADC and VDV reproducibility was evaluated using linear regression, intraclass correlation coefficients (ICC) and Lin's concordance correlation coefficients (CCC).

RESULTS

ADC reproducibility was high for same-day rescan (r(2) = 0.934) and 7-day rescan (r(2) = 0.960, ICC and CCC of 0.96 and 0.98, respectively). Same-day rescan VDV reproducibility evaluated using the ICC and CCC (0.97 and 0.98, respectively) as well as linear regression (r(2) = 0.941) was also high, but VDV 7-day rescan reproducibility was lower and significantly different (r(2) = 0.576, P < .001, ICC 0.74, CCC 0.75, P < .01).

CONCLUSIONS

Hyperpolarized (3)He MRI was well-tolerated in subjects with stage II and stage III COPD. Seven-day repeated scanning was highly reproducible for ADC and moderately reproducible for VDV.