Spiral versus electron-beam CT for coronary artery calcium scoring.

PURPOSE: To determine differences in coronary artery calcium detection, quantification, and reproducibility, as measured at electron-beam computed tomography (CT) and subsecond spiral CT with retrospective electrocardiogram gating in an asymptomatic adult population. MATERIALS AND METHODS: Seventy subjects asymptomatic for coronary heart disease underwent both electron-beam CT and subsecond spiral CT. In all subjects, two images each were obtained with both scanners. Two experienced readers using three different algorithms scored each of the four scans: one score for the electron-beam CT images and two scores for the spiral CT images. RESULTS: With a 130-HU threshold for the quantification of calcium, there were no significant differences in interscan and interobserver variation in calcium scores between the electron-beam CT and spiral CT images. There was greater interobserver (P <.001) and interscan (P <.03) variation in scores when a 90-HU threshold was used for spiral CT images. With a 130-HU threshold, when calcium scores were used for clinical risk stratification, there was a significant difference between the results obtained with electron-beam CT and those obtained with spiral CT (P <.05). CONCLUSION: Spiral CT has not yet proved to be a feasible alternative to electron-beam CT for coronary artery calcium quantification. There are systematic differences between calcium scores obtained with single-detector array subsecond spiral CT and those obtained with electron-beam CT.

Knowledge-based segmentation of thoracic computed tomography images for assessment of split lung function.

The assessment of differential left and right lung function is important for patients under consideration for lung resection procedures such as single lung transplantation. We developed an automated, knowledge-based segmentation algorithm for purposes of deriving functional information from dynamic computed tomography (CT) image data. Median lung attenuation (HU) and area measurements were automatically calculated for each lung from thoracic CT images acquired during a forced expiratory maneuver as indicators of the amount and rate of airflow. The accuracy of these derived measures from fully automated segmentation was validated against those from segmentation using manual editing by an expert observer. A total of 1313 axial images were analyzed from 49 patients. The images were segmented using our knowledge-based system that identifies the chest wall, mediastinum, trachea, large airways and lung parenchyma on CT images. The key components of the system are an anatomical model, an inference engine and image processing routines, and segmentation involves matching objects extracted from the image to anatomical objects described in the model. The segmentation results from all images were inspected by the expert observer. Manual editing was required to correct 183 (13.94%) of the images, and the sensitivity, specificity, and accuracy of the knowledge-based segmentation were greater than 98.55% in classifying pixels as lung or nonlung. There was no significant difference between median lung attenuation or area values from automated and edited segmentations (p > 0.70). Using the knowledge-based segmentation method we can automatically derive indirect quantitative measures of single lung function that cannot be obtained using conventional pulmonary function tests.

Interscan variation in coronary artery calcium quantification in a large asymptomatic patient population.

OBJECTIVE: We evaluated interscan variation in coronary artery calcium scores in a large screening population as determined by electron beam CT. MATERIALS AND METHODS: One thousand patients (average age, 53 years; age range, 18-85 years) who were asymptomatic for coronary artery disease underwent two consecutive scans of the heart on an electron beam CT scanner. Scans were performed with ECG gating, breath-hold, 3-mm collimation, and 100-msec exposure. Two contiguous pixels with density values greater than 130 H were used as the minimum criterion for a calcific lesion. The calcium score was determined on a vessel-by-vessel basis for both scans of each patient. Interscan variation in calcium and vessels involved with calcification was evaluated on the basis of age, sex, and average calcium score. RESULTS: The percentage of difference between calcium scores in scans was 28.4% and 43.0% for women and men, respectively. For the individual epicardial arteries (left main, left anterior descending, circumflex, and right coronary), the percentage of difference for calcium scores was 20.2-24.2% for women and 30.5-44.9% for men. A difference between the two scans in at least one vessel of the total coronary arteries identified with calcium was noted in 31% of patients. CONCLUSION: Interscan variability in calcium scores may be important in the determination of risk stratification. Subjects with a nonzero calcium score may benefit from undergoing two scans at the time of initial imaging.

Comparative effects of hydrofluoroalkane and chlorofluorocarbon beclomethasone dipropionate inhalation on small airways: assessment with functional helical thin-section computed tomography.

A double-blind, randomized, parallel-group pilot study compared the relative efficacy of hydrofluoroalkane-134a beclomethasone dipropionate (HFA-BDP [QVAR]; mass median aerodynamic diameter, 0. 8-1.2 m) versus cholorofluorocarbon-11/12 BDP (CFC-BDP [Beclovent]; mass median aerodynamic diameter, 3.5-4.0 m) in 31 steroid naive patients with mild to moderate asthma (PC(20,) 4 mg/mL). Functional high-resolution computed tomography was used to assess the relative efficacy of HFA-BDP and CFC-BDP on regional air trapping, as an indirect measure of small airways function and on regional hyperreactivity. Pretreatment functional computed tomography was performed at residual volume before and after methacholine challenge. After 4 weeks of treatment, functional imaging was repeated before and after the same concentration of methacholine that was administered before the treatment (n = 19 patients). Quantitative assessment of changes in distribution of lung attenuation was performed. After 4 weeks of treatment, the HFA-BDP group showed significantly more improvement in air trapping overall (a shift in the lung attenuation curve at residual volume toward more attenuation) on the posttreatment computed tomography scan (P <.05; Fisher's Exact Test). After an equal constrictor stimulus (methacholine concentration), subjects treated with HFA-BDP (n = 10 patients) showed less increase in air trapping overall than subjects treated with CFC-BDP (n = 9 patients) on the posttreatment scans compared with the pretreatment scans (P <.001; Fisher's Exact Test). No significant difference was demonstrated between the 2 treatment groups with respect to improvement in symptoms, spirometry, or methacholine responsiveness assessed by FEV(1), except for a greater reduction in breathlessness in the HFA-BDP group (P <.05). We conclude that HFA-BDP may have greater efficacy in the peripheral airways and that this effect is better assessed with functional imaging computed tomography techniques than with conventional physiologic tests.

Automated measurement of single and total lung volume from CT.

PURPOSE: The goal of this work was to develop an automated method for calculating single (SLV) and total (TLV) lung volumes from CT images. METHOD: Patients underwent volumetric CT scanning through the entire chest in a single breath-hold, as well as pulmonary function tests. An automated, knowledge-based system was developed to segment the lungs in the CT images. Image-processing routines were used to extract sets of voxels from the image data that were identified by matching them to anatomical objects defined in a model. SLV and TLV were calculated by summing included voxels. RESULTS: For 43 patients analyzed, TLV from CT and total lung capacity from body plethysmography were strongly correlated (r = 0.90). On average, the CT-derived volume of the left lung accounted for 47.2% of the total. CONCLUSION: A knowledge-based approach to segmentation of the lungs in CT can be used to automatically estimate SLV and TLV.

Electron-beam CT: the effect of using a correction function on coronary artery calcium quantitation.

PURPOSE: The purpose of the study was to determine if use of a correction function derived from a phantom with known calcium density reduces variation in coronary artery calcium scores measured with electron-beam computed tomography (CT) and to evaluate the influence of body girth, as measured by body mass index (BMI), on coronary artery calcium-score variability in a clinical screening cohort. MATERIALS AND METHODS: Two hundred fifty consecutive patients underwent two electron-beam CT examinations with a standardized phantom. Region-of-interest (ROI) measurements of the phantom were correlated with the patient BMI. In a subset of 28 patients with low but positive coronary artery calcium scores, ROI values of the phantom were used as a correction for signal attenuation. RESULTS: Patient BMI was not significantly correlated to signal attenuation. Application of a correction function resulted in a small but insignificant decrease in interscan coronary artery calcium-score variation. The interscan coronary artery calcium score variation was 24.5% +/- 23.9; it decreased to 24.3% +/- 21.6 with use of the 75 mg/cm3 portion of the phantom and to 22.2% +/- 21.4 with use of the 150 mg/cm3 portion of the phantom. CONCLUSION: The use of a coronary artery calcium phantom does not reduce interscan variation sufficiently to warrant regular clinical usage. Interscan variation in the coronary artery calcium score is not significantly influenced by patient BMI.

Detection of pulmonary emboli at the segmental and subsegmental level with electron-beam CT: validation in a porcine model.

RATIONALE AND OBJECTIVES: The authors evaluated the sensitivity of electron-beam computed tomography (CT) in the detection of segmental and subsegmental pulmonary artery emboli in a porcine model. MATERIALS AND METHODS: Twenty-one segmental and subsegmental branch pulmonary arteries in five swine were selectively catheterized and embolized with gelatin sponge pledgets. The presence of emboli was confirmed by means of contrast material-enhanced angiography. Contrast-enhanced CT scans of the pulmonary arteries were then obtained with 3-mm collimation, 2-mm table travel between sections, and an imaging time of 100 msec per section. Contrast material was injected at a rate of 2-3 mL/sec, depending on the animal's weight, with a total dose of 60 mL for each scan. Cardiac-gated and nongated scans were obtained, but breath holding was not possible in these animals. RESULTS: Contrast-enhanced electron-beam CT scanning allowed correct prospective identification of 18 of 21 emboli in the segmental and subsegmental branches of the pulmonary arteries. The overall sensitivity was 86%. Cardiac gating subjectively improved image quality but did not result in greater sensitivity in the detection of emboli. The level of sensitivity was not affected by the use of breath holding. CONCLUSION: Contrast-enhanced electron-beam CT is a sensitive method for the detection of embolism in the segmental and subsegmental pulmonary arteries.

Coronary artery calcium: alternate methods for accurate and reproducible quantitation.

RATIONALE AND OBJECTIVES: The aim of this study was to determine a more precise and accurate method of quantitating coronary artery calcium (CAC) detected with electron-beam computed tomography (CT) in patients with low CAC scores. MATERIALS AND METHODS: Two 40-section, 3-mm-collimation, electrocardiographically gated electron-beam CT examinations of the heart were performed in each patient. Fifty patients with average scores between 2 and 100, as determined with the conventional scoring algorithm, were selected. The modified conventional scoring algorithm was compared with two techniques: calculated calcium volume and approximated calcium mass. RESULTS: The percentage difference between scans ranged from 37.2% for the conventional scoring method to 28.2% and 28.4% for volume- and mass-based methods, respectively. Increasing lesion size thresholds does not improve quantitative precision and reduces accuracy in patients with small amounts of CAC. CONCLUSION: Quantification methods based on calcification volume or mass decrease score variation compared with the conventional scoring method, and increased size threshold does not improve accuracy.

Prevention of hemobilia during percutaneous biliary drainage: long-term follow-up.

PURPOSE: The authors evaluated a technique for the prevention of hemobilia when placing transhepatic biliary drainage catheters (THBDCs). MATERIALS AND METHODS: Initially, 20 patients were randomized into two groups. In the control group, a THBDC was placed after blind needle passage without contrast material opacification of the needle tract. In the experimental group, the tract was studied and then abandoned if a major vascular structure was encountered. Once a tract was found that did not traverse a major vascular structure, a THBDC was placed. An additional 35 patients undergoing 40 procedures were studied with use of the technique as outlined for the original experimental group. The original experimental group patients and the additional 35 patients were followed for up to 3 years. RESULTS: There were three cases of hemobilia in the initial control group. None of the patients in the initial experimental group experienced hemobilia. In the additional 35 patients, there were three cases of bloody drainage from the THBDC; however, the etiology of hemobilia was not secondary to transgression of a vascular structure. CONCLUSION: Visualization of the tract prevents the usage of tracts that communicate with large vascular structures. This technique reduces the incidence of hemobilia when placing THBDCs.

Clinical and angiographic selection factors for thrombolysis as initial therapy for acute lower limb ischemia.

The purpose of this study was to determine whether angiographic patterns correlate with the clinical severity of acute lower limb ischemia (ALLI) and with the outcome of treatment with percutaneous intraarterial thrombolysis (PIAT). A retrospective analysis was conducted of angiograms and case records of 186 consecutive PIAT infusions in 160 patients with ALLI. The number of segments of occlusions; associated stenoses of inflow, outflow, and collateral vessels; and the demonstration of patent distal vessels were correlated with severity of ischemia and outcome of PIAT. Occlusions requiring flow to traverse one collateral bed to supply patent distal vessels (angiographic category I) correlated with the "viable" clinical classification of ALLI. Those requiring blood to flow through two contiguous collateral beds to supply patent distal vessels (category II) correlated with the "threatened" clinical classification. Occlusions with distal propagation that occluded the distal vascular bed (category III) correlated with the "irreversible" clinical category. Rates at 30 days for patency, amputation, and mortality were as follows for category I: 100%, 0%, and 0%; category II: 90%, 8.6%, and 0.7%; and category III: 55%, 19%, and 5%, respectively. Angiographic patterns correlate well with clinical severity of ischemia and predict the outcome from PIAT as initial therapy of ALLI. Amputation and mortality rates are less than those reported for emergency surgical treatment of ALLI.