Ulrich Baum

Detection of Coronary Artery Stenoses With Thin-Slice Multi-Detector Row Spiral Computed Tomography and Multiplanar Reconstruction

Background—We analyzed the accuracy of multi-detector row spiral computed tomography (MDCT) using a 16-slice CT scanner with improved spatial and temporal resolution, as well as routine premedication with &bgr;-blockers for detection of coronary stenoses. Methods and Results—Seventy-seven patients with suspected coronary disease were studied by MDCT (12×0.75-mm cross-sections, 420 ms rotation, 100 mL contrast agent IV at 5 mL/s). Patients with a heart rate above 60/min received 50 mg atenolol before the scan. In axial MDCT images and multiplanar reconstructions, all coronary arteries and side branches with a diameter of 1.5 mm or more were assessed for the presence of stenoses exceeding 50% diameter reduction. In comparison to invasive coronary angiography, MDCT correctly classified 35 of 41 patients (85%) as having at least 1 coronary stenosis and correctly detected 57 of 78 coronary lesions (73%). After excluding 38 of 308 coronary arteries (left main, left anterior descending, left circumflex, and right coronary artery in 77 patients) classified as unevaluable by MDCT (12%), 57 of 62 lesions were detected, and absence of stenosis was correctly identified in 194 of 208 arteries (sensitivity: 92%; specificity: 93%; accuracy: 93%; positive and negative predictive values: 79% and 97%). Conclusions—MDCT coronary angiography with improved spatial resolution and premedication with oral &bgr;-blockade permits detection of coronary artery stenoses with high accuracy and a low rate of unevaluable arteries.

Detection of Calcified and Noncalcified Coronary Atherosclerotic Plaque by Contrast-Enhanced, Submillimeter Multidetector Spiral Computed Tomography A Segment-Based Comparison With Intravascular Ultrasound

Background—We investigated the ability of multidetector spiral computed tomography (MDCT) to detect atherosclerotic plaque in nonstenotic coronary arteries. Methods and Results—In 22 patients without significant coronary stenoses, contrast-enhanced MDCT (0.75-mm collimation, 420-ms rotation) and intravascular ultrasound (IVUS) of one coronary artery were performed. A total of 83 coronary segments were imaged by IVUS (left main, 19; left anterior descending, 51; left circumflex, 4; right coronary, 9). MDCT data sets were evaluated for the presence and volume of plaque in the coronary artery segments. Results were compared with IVUS in a blinded fashion. For the detection of segments with any plaque, MDCT had a sensitivity of 82% (41 of 50) and specificity of 88% (29 of 33). For calcified plaque, sensitivity was 94% (33 of 36) and specificity 94% (45 of 47). Coronary segments containing noncalcified plaque were detected with a sensitivity of 78% (35 of 45) and specificity of 87% (33 of 38), but presence of exclusively noncalcified plaque was detected with only 53% sensitivity (8 of 15). If analysis was limited to the 41 proximal segments (segments 1, 5, 6, and 11 according to American Heart Association classification), sensitivity and specificity were 92% and 88% for any plaque, 95% and 91% for calcified plaque, and 91% and 89% for noncalcified plaque. MDCT substantially underestimated plaque volume per segment as compared with IVUS (24±35 mm3 versus 43±60 mm3, P <0.001). Conclusions—The results indicate the potential of MDCT to detect coronary atherosclerotic plaque in patients without significant coronary stenoses. However, further improvements in image quality will be necessary to achieve reliable assessment, especially of noncalcified plaque throughout the coronary tree.

Detection of Coronary Artery Stenoses by Contrast-Enhanced, Retrospectively Electrocardiographically-Gated, Multislice Spiral Computed Tomography

Background—Multislice spiral computed tomography (MSCT) with retrospectively ECG-gated image reconstruction permits coronary artery visualization. We investigated the method’s ability to identify high-grade coronary artery stenoses and occlusions. Methods and Results—A total of 64 consecutive patients were studied by MSCT (4×1 mm cross-sections, 500-ms rotation, table feed 1.5 mm/rotation, intravenous contrast agent, retrospectively ECG-gated image reconstruction). All coronary arteries and side branches with a luminal diameter ≥2.0 mm were assessed concerning evaluability and the presence of high-grade stenoses (>70% diameter stenosis) or occlusions. Results were compared with quantitative coronary angiography. Of 256 coronary arteries (left main, left anterior descending, left circumflex and right coronary artery, including their respective side branches), 174 could be evaluated (68%). In 19 patients (30%), all arteries were evaluable. Artifacts caused by coronary motion were the most frequent reason for unevaluable arteries. Overall, 32 of 58 high-grade stenoses and occlusions were detected by MSCT (58%). In evaluable arteries, 32 of 35 lesions were detected, and the absence of stenosis was correctly identified in 117 of 139 arteries (sensitivity, 91%; specificity, 84%). If analysis was extended to all stenoses with >50% diameter reduction, sensitivity was 85% (40 of 47) and specificity was 76% (96 of 127). Conclusions—MSCT with retrospective ECG gating permits the detection of coronary artery stenoses with high accuracy if image quality is sufficient, but its clinical use may presently be limited due to degraded image quality in a substantial number of cases, mainly due to rapid coronary motion.

Subsecond multi-slice computed tomography: basics and applications

The recent advent of multislice-scanning is the first real quantum leap in computed tomography since the introduction of spiral CT in the early 90s. We discuss basic theoretical considerations important for the design of multislice scanners. Then, specific issues, like the design of the detector and spiral interpolation schemes are addressed briefly for the SOMATOM PLUS 4 Volume Zoom. The theoretical concepts are validated with phantom measurements. We finally show the large potential of the new technology for clinical applications. The concurrent acquisition of multiple slices results in a dramatic reduction of scan time for a given scan technique. This allows scanning volumes previously inaccessible. Similarly, given volumes can be scanned at narrower collimation, i.e. higher axial resolution in a given time. From data acquired at narrow collimation, both high-resolution studies and standard images can be reconstructed in the so-called Combi-Mode. This on the one hand reduces dose exposure to the patient because repeated scanning of a patient is no longer required. On the other hand, standard reconstructions benefit from narrow collimation as Partial Volume Artifacts are drastically suppressed. The rotational speed of 0.5 s of the SOMATOM PLUS 4 Volume Zoom furthermore opens up a whole range of new applications in cardiac CT. For the first time, virtually motion-free images can be acquired even for large volumes in a single breathhold by the combination of fast rotation and ECG triggering, respectively gating. We explain the underlying concepts and present initial results. The paper concludes with a brief discussion of the impact of the new technique on image display and postprocessing.

Diagnostic accuracy of noninvasive coronary angiography in patients after bypass surgery using 64-slice spiral computed tomography with 330-ms gantry rotation

Background— Multidetector computed tomographic angiography (MDCT) has been shown to allow detection of coronary artery bypass graft (CABG) occlusions and stenoses. However, the assessment of native coronary arteries in addition to CABG has thus far not been sufficiently validated. Methods and Results— Fifty patients with a total of 138 CABG (34 mammary grafts, 3 radial grafts, 101 venous grafts) were investigated by MDCT (0.6-mm collimation, 32 detector rows, 2 focal points, 330-ms rotation) 9 to 252 months (mean, 106 months) after surgery. CABG and all native coronary arteries with a diameter of >1.5 mm were evaluated for the presence of significant stenoses (≥50% diameter reduction). Results were compared with quantitative coronary angiography. By MDCT, all CABG were evaluable and were correctly classified as occluded (n=38) or patent (n=100). Sensitivity for stenosis detection in patent grafts was 100% (16/16) with a specificity of 94% (79/84). For the per-segment evaluation of native coronary arteries and distal runoff vessels, sensitivity in evaluable segments (91%) was 86% (87/101) with a specificity of 76% (354/465). If evaluation was restricted to nongrafted arteries and distal runoff vessels, sensitivity was 86% (38/44) with a specificity of 90% (302/334). On a per-patient basis, classifying patients with at least 1 detected stenosis in a CABG, a distal runoff vessel, or a nongrafted artery or with at least 1 unevaluable segment as “positive,” MDCT yielded a sensitivity of 97% (35/36) and specificity of 86% (12/14). Conclusions— We found that 64-slice MDCT permits the evaluation of bypass grafts and the assessment of the native coronary arteries for the presence of stenosis.

Dose reduction in computed tomography by attenuation-based on-line modulation of tube current: evaluation of six anatomical regions.

Abstract. This study investigated the potential of attenuation-based on-line modulation of tube current to reduce the dose of computed tomography (in milliamperes) without loss in image quality. The dose can be reduced for non-circular patient cross-sections by reducing the tube current at the angular positions at which the diameter through the patient diameter is smallest. We investigated a new technical approach with attenuation-based on-line modulation of tube current. Computed tomographic projection data were analyzed to determine the optimal milliampere values for each projection angle in real time, instead of performing prior measurements with localizer radiographs. We compared image quality, noise pattern, and dose for standard scans and for scans with attenuation-based on-line modulation of tube current in a group of 30 radiation therapy patients. Six different anatomical regions were examined: head, shoulder, thorax, abdomen, pelvis, and extremities (knee). Image quality was evaluated by four radiologists in a blinded fashion. We found the dose to be reduced typically by 15–50 %. In general, no deterioration in image quality was observed. Thus the dose in computed tomography be reduced substantially by technical measures without sacrificing image quality. Attenuation-based on-line modulation of tube current is an efficient and practical means for this.

Investigation of Aortocoronary Artery Bypass Grafts by Multislice Spiral Computed Tomography With Electrocardiographic-Gated Image Reconstruction

MK, Popma JJ, Leon MB. Increased restenosis in diabetes mellitus after coronary interventions is due to exaggerated intimal hyperplasia: a serial intravascular ultrasound study. Circulation 1997;95:1366–1369. 17. Kastrati A, Shoming A, Elezi S, Shuhlen H, Dirschinger J, Hadamitzky M, Wehinger A, Hausleiter J, Walter H, Neumann FJ. Predictive factors of restenosis after coronary stent placement. J Am Coll Cardiol 1997;30:1428–1436. 18. Akiyama T, Moussa I, Reimers B, Ferraro M, Kobayashi Y, Blengino S, Di Francesco L, Finci L, Di Mario C, Colombo A. Angiographic and clinical outcome following coronary stenting of small vessels. A comparison with coronary stenting of large vessels. J Am Coll Cardiol 1998;32:1610–1618. 19. Lau KW, Ding ZP, Sim LL, Sigwart U. Clinical and angiographic outcome after angiographically-guided stent placement in small coronary vessels. Am Heart J 2000;139:830–839.

Dose reduction in CT examination of children by an attenuation-based on-line modulation of tube current (CARE Dose)

Abstract. In a controlled patient study we investigated the potential of attenuation-based on-line modulation of the tube current to reduce milliampere values (mAs) in CT examinations of children without loss of image quality. mAs can be reduced for non-circular patient cross sections without an increase in noise if tube current is reduced at those angular positions where the patient diameter and, consequently, attenuation are small. We investigated a technical approach with an attenuation-based on-line control for the tube current realised as a work-in-progress implementation. The CT projection data are analysed in real time to determine optimal mAs values for each projection angle. We evaluated mAs reduction for 100 spiral CT examinations with attenuation-based on-line modulation of the tube current in a group of children. Two radiologists evaluated image quality by visual interpretation in consensus. We compared the mAs values read from the CT scanner with preset mAs of a standard protocol. Four different scan regions were examined in spiral technique (neck, thorax, abdomen, thorax and abdomen). We found the mAs product to be reduced typically by 10–60% depending on patient geometry and anatomical regions. The mean reduction was 22.3% (neck 20%, thorax 23%, abdomen 23%, thorax and abdomen 22%). In general, no deterioration of image quality was observed. There was no correlation between the age and the mean mAs reduction in the different anatomical regions. By classifying the children respectively to their weight, there is a positive trend between increasing weight and mAs reduction. We conclude that mAs in spiral CT examinations of children can be reduced substantially by attenuation-based on-line modulation of the tube current without deterioration of image quality. Attenuation-based on-line modulation of tube current is efficient and practical for reducing dose exposure to children.

Head and neck tumors: imaging recurrent tumor and post-therapeutic changes with CT and MRI.

OBJECTIVE To evaluate criteria for detection of tumor recurrence and post-treatment changes in patients with head and neck malignancies in computed tomography (CT) and magnetic resonance imaging (MRI). METHODS AND MATERIALS Thirty-nine patients with head and neck carcinoma receiving radiochemotherapy were examined before, during and after therapy with MRI. Changes in signal intensity were correlated to histology or clinical course. Three hundred and thirty-one patients with head and neck malignancies were examined with CT after therapy. CT diagnoses were correlated with histology or clinical course. RESULTS Main criteria for recurrent/residual tumor in MRI was infiltrative mass with high signal intensity in T2-weighted images and enhancement after Gd-DTPA in T1-weighted images. Radiation-induced changes led to false positive diagnosis in 46% in the interval up to 3 months after therapy and in 58% in the interval 3-6 months after therapy. The combination of a circumscribed, infiltrative mass with contrast enhancement in CT had a sensitivity of 86% and a specificity of 80%. CONCLUSION CT could accurately demonstrate postoperative changes and tumor recurrence. MRI had advantages in differentiation of tumor and scar, but edema after radiation therapy can spoil diagnosis.

Phase I trial of strictly time-scheduled gemcitabine and cisplatin with concurrent radiotherapy in patients with locally advanced pancreatic cancer

PURPOSE Maximal therapeutic gain in xenograft sarcoma and toxicity for jejunal mucosa is time dependent for concurrent gemcitabine and radiotherapy (RT). We used a time-dependent schedule to determine the maximal-tolerated dose and dose-limiting toxicities (DLTs; Grade 4 hematologic or Grade 3 other toxicity). METHODS AND MATERIALS Patients with pancreatic cancer (n = 33), periampullary carcinoma (n = 1), or bile duct cancer (n = 2) were treated with 3-day conformal RT with 50.4 Gy (tumor, lymphatics) plus a 5.4-Gy boost. Concurrent cisplatin (20 mg/m(2)/d on Days 1-5 and 29-33) and gemcitabine (initially 600 mg/m(2), weekly on Fridays 68 h before RT) were administered. Because of DLT, the doses were reduced to 500 mg/m(2) weekly and then 500, 400, or 300 mg/m(2) on Days 2, 5, 26, 33. RESULTS DLT occurred at all dose levels of gemcitabine >300 mg/m(2). Fourteen patients were treated at the recommended Phase II dose of gemcitabine (300 mg/m(2)) without DLT. The response to chemoradiation allowed 10 of 30 initially unresectable patients with primary pancreatic carcinoma to undergo radical surgery, including a complete response in 2 cases. CONCLUSIONS At the recommended Phase II dose, chemoradiation with gemcitabine and cisplatin can be administered safely in pancreatic carcinoma. However, at higher dose levels, toxicity is severe and frequent. Patients with a chance for conversion to resection could benefit from this schedule.