Biomedical subjects

Thomas G Flohr

Publications and source records attributed to Thomas G Flohr.

15 recordsLinked to original sources

PubMed2006

Variability of aortic valve calcification measurement with multislice spiral computed tomography.

OBJECTIVES: We sought to assess the variability of aortic valve calcifications (AVCs) regarding the reconstruction window at different heart phases using multislice-spiral computed tomography. MATERIALS AND METHODS: A total of 46 patients (26 men; mean age. 65 years) underwent AVC scoring with multislice-spiral computed tomography (12 x 0.75 mm, 120 kV, 133 mAseff). Image reconstruction was performed every 10% of the RR-interval (0-90%). AVC was quantified using Agatston score, calcium volume, and calcium mass. Images were assessed for least motion artifacts. Coefficients of variation and Wilcoxon test were calculated. RESULTS: AVC scores are lowest at 60% and highest at 0% of the RR-interval (P < 0.001). Mean coefficients of variation were 36.2% (Agatston score), 38.7% (calcium volume), and 32.9% (calcium mass). At 60% (50-70%). minimal motion artifacts and the lowest variability of the scores were found. CONCLUSIONS: AVC scores show large variability depending on the point of image reconstruction. Diastolic image reconstruction at 60% of the RR-interval is recommended.

Adult↗

PubMed2006

Thick maximum intensity projections for the assessment of left ventricular function with 64-slice computed tomography.

OBJECTIVE: The objective of this study was to assess the accuracy of thick maximum intensity projections (MIP) from computed tomography (CT) data sets mimicking projection images from biplane ventriculography for evaluation of left ventricular (LV) parameters. MATERIALS AND METHODS: Fifty-eight patients underwent 64-slice CT. Multiphase images were reconstructed in 10% steps of the RR interval. MIP images (70-mm thickness) of the contrast-enhanced LV in fixed 30 degrees right anterior oblique (RAO)/60 degrees left anterior oblique (LAO) and in adapted short-/long-axis planes were reconstructed. LV parameters were calculated using the area-length method formula. Three-dimensional assessment with semiautomated software served as reference standard. RESULTS: Use of thick MIP reconstructions had a high intermethod reliability (86-94%) compared with the 3-dimensional approach. Smaller measurement errors were found for thick MIP reconstructions in adapted short-/long-axis planes. A significant projection error (3.0%, P < 0.001) of thick MIP reconstructions was found using fixed 30 degrees RAO/60 degrees LAO compared with adapted short-/long-axis reconstructions. CONCLUSION: Thick MIP reconstructions with adapted short-/long-axis planes allow an accurate assessment of LV parameters compared with the established 3-dimensional method.

Adult↗

PubMed2006

Small pulmonary nodules: effect of two computer-aided detection systems on radiologist performance.

PURPOSE: To prospectively compare the effects of two computer-aided detection (CAD) systems on the detection of small pulmonary nodules at multi-detector row computed tomography (CT) by using a consensus panel decision as the reference standard. MATERIALS AND METHODS: Institutional review board approval and informed consent were obtained. Multi-detector row CT scans were randomly chosen and prospectively evaluated in 25 patients. Two dedicated CAD systems-ImageChecker CT (R2 Technologies, Sunnyvale, Calif) and Nodule Enhanced Viewing (NEV) (Siemens Medical Solutions, Forchheim, Germany)-were used. Results were interpreted by three radiologists with 1, 3, and 6 years of experience. Images were evaluated without and with CAD software. The reference standard was assessed by a consensus panel consisting of all three radiologists and an adjudicator with 8 years of experience. RESULTS: A total of 116 pulmonary nodules (average diameter, 3.4 mm; average volume, 32.05 mm3) were found in all data sets during consensus interpretation, which included findings from the CAD software and all radiologists. Overall sensitivity was 73% with ImageChecker CT and 75% with NEV. Overall sensitivity without CAD was 68% for radiologist 1, 78% for radiologist 2, and 82% for radiologist 3. With ImageChecker CT, sensitivity increased to 79% for radiologist 1, 90% for radiologist 2, and 84% for radiologist 3. With NEV, sensitivity increased to 79% for radiologist 1, 90% for radiologist 2, and 86% for radiologist 3. The average number of false-positive findings was six (range, 0-14) with ImageChecker CT and eight (range, 0-22) with NEV. CONCLUSION: Radiologist performance in the interpretation of multi-detector row CT scans can be improved by using CAD systems, with a reduction in the number of false-negative diagnoses. No statistically significant difference in sensitivity was found between the two CAD systems.

Adult↗

PubMed2006

Improving diagnostic accuracy of MDCT coronary angiography in patients with mild heart rhythm irregularities using ECG editing.

OBJECTIVE: The objective of our study was to compare diagnostic accuracy of MDCT coronary angiography in a population of patients with mild heart rhythm irregularities before and after editing the ECG. SUBJECTS AND METHODS: Thirty-eight patients who underwent MDCT coronary angiography and conventional coronary angiography were enrolled in the study. The inclusion criterion was the presence of mild heart rhythm irregularities (i.e., premature beats; atrial fibrillation; mistriggering; or low heart rate, defined as 40 beats per minute or less) during the scan. All patients underwent MDCT with the following parameters: 16 detectors; collimation, 0.75 mm; gantry rotation time, 375 msec; 120 kV; and effective milliampere-second setting, 500-600. Images were reconstructed in two settings: before ECG editing and after ECG editing (i.e., arbitrary modification of temporal windows within the cardiac cycle at the site of mild heart rhythm irregularities). Data sets were scored for the presence of significant stenoses (> or = 50% lumen reduction) in coronary segments > or = 2 mm diameter. The results of the two groups were compared with a McNemar test, and a p value of less than 0.05 was considered significant. RESULTS: The sensitivity, specificity, and negative and positive predictive values of MDCT coronary angiography for the detection of significant stenoses before and after ECG editing were 63% (41/65) and 92% (78/85); 97% (251/260) and 96% (305/317); 87% (62/71) and 87% (81/93); 91% (251/275) and 97% (305/313), respectively (p < 0.05). The proportion of nonassessable segments was reduced from 17% (70/416) before ECG editing to 2% (10/416) after. CONCLUSION: ECG editing significantly improves diagnostic accuracy in a selected population of patients with mild heart rate irregularities.

Atrial Fibrillation↗

PubMed2005

Global left ventricular function in cardiac CT. Evaluation of an automated 3D region-growing segmentation algorithm.

The purpose was to evaluate a new semi-automated 3D region-growing segmentation algorithm for functional analysis of the left ventricle in multislice CT (MSCT) of the heart. Twenty patients underwent contrast-enhanced MSCT of the heart (collimation 16 x 0.75 mm; 120 kV; 550 mAseff). Multiphase image reconstructions with 1-mm axial slices and 8-mm short-axis slices were performed. Left ventricular volume measurements (end-diastolic volume, end-systolic volume, ejection fraction and stroke volume) from manually drawn endocardial contours in the short axis slices were compared to semi-automated region-growing segmentation of the left ventricle from the 1-mm axial slices. The post-processing-time for both methods was recorded. Applying the new region-growing algorithm in 13/20 patients (65%), proper segmentation of the left ventricle was feasible. In these patients, the signal-to-noise ratio was higher than in the remaining patients (3.2+/-1.0 vs. 2.6+/-0.6). Volume measurements of both segmentation algorithms showed an excellent correlation (all P<or=0.0001); the limits of agreement for the ejection fraction were 2.3+/-8.3 ml. In the patients with proper segmentation the mean post-processing time using the region-growing algorithm was diminished by 44.2%. On the basis of a good contrast-enhanced data set, a left ventricular volume analysis using the new semi-automated region-growing segmentation algorithm is technically feasible, accurate and more time-effective.

Aged↗

PubMed2005

First performance evaluation of a dual-source CT (DSCT) system.

We present a performance evaluation of a recently introduced dual-source computed tomography (DSCT) system equipped with two X-ray tubes and two corresponding detectors, mounted onto the rotating gantry with an angular offset of 90 degrees . We introduce the system concept and derive its consequences and potential benefits for electrocardiograph [corrected] (ECG)-controlled cardiac CT and for general radiology applications. We evaluate both temporal and spatial resolution by means of phantom scans. We present first patient scans to illustrate the performance of DSCT for ECG-gated cardiac imaging, and we demonstrate first results using a dual-energy acquisition mode. Using ECG-gated single-segment reconstruction, the DSCT system provides 83 ms temporal resolution independent of the patient's heart rate for coronary CT angiography (CTA) and evaluation of basic functional parameters. With dual-segment reconstruction, the mean temporal resolution is 60 ms (minimum temporal resolution 42 ms) for advanced functional evaluation. The z-flying focal spot technique implemented in the evaluated DSCT system allows 0.4 mm cylinders to be resolved at all heart rates. First clinical experience shows a considerably increased robustness for the imaging of patients with high heart rates. As a potential application of the dual-energy acquisition mode, the automatic separation of bones and iodine-filled vessels is demonstrated.

Coronary Angiography↗

PubMed2005

Multi-detector row CT systems and image-reconstruction techniques.

The introduction in 1998 of multi-detector row computed tomography (CT) by the major CT vendors was a milestone with regard to increased scan speed, improved z-axis spatial resolution, and better utilization of the available x-ray power. In this review, the general technical principles of multi-detector row CT are reviewed as they apply to the established four- and eight-section systems, the most recent 16-section scanners, and future generations of multi-detector row CT systems. Clinical examples are used to demonstrate both the potential and the limitations of the different scanner types. When necessary, standard single-section CT is referred to as a common basis and starting point for further developments. Another focus is the increasingly important topic of patient radiation exposure, successful dose management, and strategies for dose reduction. Finally, the evolutionary steps from traditional single-section spiral image-reconstruction algorithms to the most recent approaches toward multisection spiral reconstruction are traced.

Electrocardiography↗

PubMed2005

CT for imaging coronary artery disease: defining the paradigm for its application.

Current generation multidetector-row CT (MDCT) enables high-resolution, motion-free imaging of the heart within a single, short breath-hold. MDCT allows highly accurate and reproducible quantification of coronary artery calcium, a marker that has been used for the detection, exclusion and monitoring of coronary atherosclerosis. The exact role of coronary calcium measurements for cardiac risk stratification remains unclear to date. At contrast enhanced MDCT coronary angiography coronary arteries can be visualized with unprecedented detail. The accurate non-invasive assessment of the presence and degree of coronary artery stenosis appears within reach. With increasing accuracy MDCT enables non-invasive patency evaluation of coronary artery bypass grafts and coronary stents. The cross-sectional nature of contrast enhanced MDCT coronary angiography allows assessment of the vessel wall and may permit more accurate quantification of total atherosclerotic plaque burden than measuring calcified components alone. For a limited time, future technical improvement will be pursued mainly by accelerated gantry rotation speed and additional detector rows. However, novel concepts of CT image acquisition are already under investigation and may bring about yet another quantum leap for medical CT. This communication discusses potential approaches for the beneficial utilization of MDCT for the assessment of patients with known or suspected coronary heart disease.

Coronary Angiography↗

PubMed2005

Coronary calcium scoring using 16-row multislice computed tomography: nonenhanced versus contrast-enhanced studies in vitro and in vivo.

OBJECTIVES: We sought to assess the agreement of coronary artery calcium score in nonenhanced and contrast-enhanced multislice-spiral computed tomography. MATERIALS AND METHODS: Vessel phantoms and 36 patients underwent nonenhanced and contrast-enhanced cardiac multislice-spiral computed tomography (Sensation 16; Siemens, Germany). Reconstruction-parameters: slice thickness 3 mm, increment 2 mm, kernels B35f and B30f. The Agatston score, calcium mass, and number of lesions were calculated. Images were scored using detection thresholds of 130 Hounsfield units (HU) and 350 HU. Based on the Agatston score, risk stratification was performed. RESULTS: In the phantom and patient study, altering the threshold from 130 to 350 HU led to a significant decrease in the mean Agatston score (phantom: 54.6%, patients: 66.7%) and calcium mass (33.0%, 47.0%) (B35f). Contrast-enhanced studies (threshold: 350 HU) showed an increase of the mean Agatston score (71.0%, 20.7%) and calcium mass (81.0%, 16.0%) when compared with nonenhanced scans (threshold: 350 HU). A total of 57% of all patients were assigned to different risk groups. CONCLUSIONS: Contrast material may simulate calcification; therefore, calculation of the coronary calcium score from contrast-enhanced images is not reliable.

Calcinosis↗

PubMed2005

Individually adapted examination protocols for reduction of radiation exposure for 16-MDCT chest examinations.

OBJECTIVE: The purpose of our study was to develop a simple protocol for reduction of radiation exposure without loss of diagnostic information in chest 16-MDCT. MATERIALS AND METHODS: Two hundred and four patients underwent MDCT of the thorax (Somatom Sensation 16, Siemens). Group 1 was scanned using a standard protocol with 100 mAs(effective) (mAs(eff)). Group 2 was scanned using a dose modulation template (CareDose). Group 3 was scanned with mAs(eff) = body weight (kg). Group 4 was scanned with a combination of weight-adapted mAs(eff) and dose modulation. All other parameters were kept constant. Signal-to-noise ratio was assessed as an objective measurement for image quality, and subjective image quality was rated by three experienced radiologists on a 4-point scale. Effective dose was calculated using dedicated software. RESULTS: The mean noise measurement values were 8.31 H for the 100 mAs(eff) protocol for the regression between weight and signal-to-noise (p < 0.0001), 9.08 H for group 2 (p < 0.0001), 9.0 H for group 3 (p = 0.5051), and 9.98 H for group 4 (p = 0.0152). The median image quality was 1 (1 = highest quality) in all subgroups. The mean effective dose was 6.83 mSv, 5.92 mSv, 4.73 mSv, and 3.97 mSv, respectively. The least correlation between weight and image noise was achieved for the individually weight-adapted protocol and in the weight-adapted with CareDose combination. CONCLUSION: By tube current time product adaptation (kg = mAs(eff)) combined with an online tube current modulation template, a well-balanced examination without significant loss of information was achieved for this specific scanner. Thus, individually adapted protocols for chest 16-MDCT can be recommended.

Algorithms↗

PubMed2003

Advances in cardiac imaging with 16-section CT systems.

RATIONALE AND OBJECTIVES: The authors present advances in electrocardiographically (ECG) gated cardiac spiral scanning with recently introduced 16-section computed tomographic (CT) equipment. MATERIALS AND METHODS: The authors discuss the technical principles of ECG-gated cardiac scanning. They give an overview on system properties and on the detector design. They describe ECG-gated scan- and image-reconstruction techniques and ECG-controlled dose modulation ("ECG pulsing") for a reduction of the patient dose. They discuss key parameters for image quality and present simulation and phantom studies and they give preliminary values for the patient dose. RESULTS: An extension of the adaptive cardiac volume reconstruction for ECG-gated spiral CT provides adequate image quality for up to 16 sections. With the smallest reconstructed section width (about 0.83 mm) and overlapping image reconstruction, cylindrical holes 0.6-0.7 mm in diameter can be resolved in a transverse resolution phantom independent of the heart rate. For coronary CT angiography, the influence of transverse resolution is most pronounced for coronary segments that are only slightly tilted relative to the scan plane. In this case, visualization of stents and plaques is considerably improved with 1.0-mm or smaller section width. For 0.42-second gantry rotation time, temporal resolution reaches its optimum (105 msec) at a heart rate of 81 beats per minute. Effective patient dose for the standard protocols recommended by the manufacturer ranges from 0.45 mSv (male) for ECG-triggered calcium scoring to 7.1 mSv (male) for high-resolution ECG-gated coronary CT angiography. With ECG pulsing, the dose is reduced by 30%-50% depending on the patient's heart rate. CONCLUSION: Clinical experience will be needed to evaluate fully the potential of 16-section technology for cardiac imaging.

Artifacts↗

PubMed2003

A new algorithm for metal artifact reduction in computed tomography: in vitro and in vivo evaluation after total hip replacement.

RATIONALE AND OBJECTIVES: To evaluate a newly developed algorithm for metal artifact reduction (MAR) in Computed Tomography (CT). METHODS: A projection interpolation algorithm for MAR with threshold-based metal segmentation was developed. First, the algorithm was tested with a simulated hip phantom. On demand, the presence of metallic inserts was simulated, representing total hip endoprostheses. Second, CT data of 20 patient with total hip endoprosthesis were reconstructed with and without application of the MAR algorithm. Image quality was independently assessed by 2 experienced radiologists using a qualitative score. The results of the in vitro study were evaluated with the Student's t test. Results of the in vivo study were analyzed using a repeated-measure analysis of variance. RESULTS: Applying the MAR algorithm the phantom study showed no significant difference between images with and without simulated metal contributions. The patient study revealed improved image quality using the MAR algorithm. Results were statistically significant for fat (P=0.0097), vessels (P=0.0091), and bone (P=0.0005). Improvement of the image quality for muscle was not statistically significant (P=0.0287). CONCLUSIONS: A new algorithm for metal artifact reduction was successfully introduced into clinical routine. The algorithm led to a robust reduction of metal artifacts. The MAR algorithm may serve for an improvement in image quality in patients with metallic implants.

Aged↗

PubMed2003

Multi-detector row CT versus coronary angiography: preoperative evaluation before totally endoscopic coronary artery bypass grafting.

PURPOSE: To assess multi-detector row spiral computed tomography (CT) for preoperative evaluation of patients undergoing totally endoscopic coronary artery bypass grafting and to correlate the data with coronary angiographic and intraoperative findings. MATERIALS AND METHODS: Thirty-six patients preoperatively underwent multi-detector row CT (4 x 1-mm collimation, pitch of 1.5, 500-msec rotation time, retrospective electrocardiographic gating, 1.25-mm effective section thickness) and coronary angiography. Assessment criteria for both techniques were visibility and cardiac course of coronary arteries, localization and degree of stenoses, composition of atherosclerotic plaques, and vascular diameter at anastomosis site. Site for distal bypass anastomosis was recommended. Results at multi-detector row CT were calculated relative to results at coronary angiography and surgery. RESULTS: Multi-detector row CT properly displayed 79.4% (154 of 194) of all surgical relevant coronary segments and 80.4% (434 of 540) of all coronary segments. For coronary angiography, ratios of 88.7% (172 of 194) and 94.6% (511 of 540), respectively, were observed. For detection of calcified plaques, multi-detector row CT results exceeded those at coronary angiography by a difference of 17% (18 of 18 [100%] compared with 15 of 18 [83%]). Hemodynamically relevant stenoses were identified with multi-detector row CT in 76% (42 of 55) of cases. Bridging of coronary segments through either myocardium (four of five) or epicardial fat (two of three) was better identified at multi-detector row CT than it was at coronary angiography (one of five compared with zero of three, respectively). At multi-detector row CT, 76% (28 of 37) of all distal bypass touchdown segments were identified, but at coronary angiography, only 70% (26 of 37) were identified. CONCLUSION: Multi-detector row CT provides extended information about coronary target site and therefore should be regarded as an ideal additive planning tool for complex minimally invasive procedures such as totally endoscopic coronary artery bypass grafting or minimally invasive direct coronary artery bypass grafting.

Adult↗

PubMed2003

Current concepts in multi-detector row CT evaluation of the coronary arteries: principles, techniques, and anatomy.

Cardiac imaging is becoming a practical application of mechanical computed tomography (CT) with the availability of four, eight, and 16 detector row scanners. The role of imaging is progressing from simple determination of the presence of arterial calcifications on nonenhanced scans to demonstration of vascular stenoses on coronary CT angiograms. Optimization of the imaging technique and knowledge of coronary artery anatomy are both important for the development of CT of the heart. Technical factors such as a slow heart rate, a short scanning time, subcentimeter spatial resolution, high temporal resolution, and reconstruction of multiple image data sets at various intervals in the cardiac cycle result in optimal visualization of the coronary arteries. Axial, thin-slab maximum intensity projection, and volume-rendered images are used to display the normal anatomy and anomalies of the coronary arteries. The challenges of CT angiography of the coronary arteries have been partially met and will likely be overcome with continued evolution of the technology.

Artifacts↗

PubMed2003

[Non-invasive 16-row spiral multislice computed tomography coronary angiography after one year of experience].

The gold standard for direct diagnostic imaging of coronary arteries is still conventional X-ray coronary angiography, even though for several other applications, noninvasive techniques substituted invasive ones. In the last 10 years several techniques (magnetic resonance, electron beam tomography, spiral computed tomography) attempted to emerge as noninvasive modality for the study of coronary arteries. The introduction of multislice computed tomography (MSCT) with retrospectively gated ECG reconstructions has substantially modified the coronary imaging scenario. In fact, the results have been promising since the beginning with 4-row MSCT. Currently the results reported with 16-row MSCT allow to question which role can the noninvasive coronary angiography play in clinical settings. With a scan of < 20 s after intravenous administration of iodinated contrast material it is possible to obtain information similar to conventional coronary angiography. Moreover, together with vascular patency, also atherosclerotic plaques are well visualized and characterized (type: calcified, soft, mixed). Ongoing studies are validating MSCT in the assessment of plaque vulnerability. The same technique allows to evaluate left ventricular function and myocardial wall motion impairment. Still with a few major limitations related to the heart rate, MSCT will broaden the noninvasive capability of evaluating coronary arteries in patients where conventional coronary angiography is exceeding the actual clinical question or considered as premature.

Algorithms↗