Pulmonary embolism: is multislice CT the method of choice? For.
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Angiography↗
Biomedical subjects
Mathias Prokop
Publications and source records attributed to Mathias Prokop.
Contrast-enhanced MR Angiography of the renal arteries: blinded multicenter crossover comparison of gadobenate dimeglumine and gadopentetate dimeglumine.
PURPOSE: To prospectively and intraindividually compare 0.1 mmol/kg gadobenate dimeglumine with 0.2 mmol/kg gadopentetate dimeglumine for contrast material-enhanced magnetic resonance (MR) angiography of the renal arteries. MATERIALS AND METHODS: Institutional review board approval was granted by each of three participating centers. The study accorded with international standards for good clinical practice and Declaration of Helsinki and subsequent amendments. Patients gave written informed consent before enrollment. Patients (n = 34) underwent two MR angiographic examinations more than 48 hours but less than 12 days apart. Gadobenate dimeglumine followed by gadopentetate dimeglumine was administered in 18 patients; the order of administration was reversed in 16 patients. A 1.5-T MR imager was used with a phase-encoded three-dimensional spoiled breath-hold pulse sequence. Two blinded independent readers qualitatively assessed randomized subtracted maximum intensity projection images. A three-point scale for diagnostic quality (0, poor; 1a or 1p, moderate; and 2a or 2p, adequate [a and p refer, respectively, to absence and presence of vascular lesions]) was used to score each of nine segments of the abdominal aorta and both renal arteries (possible overall score, 18). Quantitative assessment (vessel signal-to-noise ratio [SNR], vessel-muscle contrast-to-noise ratio [CNR]) of source images was performed for regions of interest in supra-, juxta-, and infrarenal aorta segments and psoas muscle. Data were tested with analysis of variance for two-period crossover design. Interreader agreement was evaluated with Cohen kappa statistics. RESULTS: No difference in mean image quality between the two contrast agents was observed; scores for gadobenate dimeglumine and gadopentetate dimeglumine were 15.15 and 15.23 for reader 1 and 16.77 and 17.01 for reader 2. The order of contrast material administration likewise produced no quality differences: readers 1 and 2 reported scores of 14.4 +/- 4.2 (standard deviation) and 16.7 +/- 2.3, respectively, when gadobenate dimeglumine was given first, and 15.2 +/- 1.8 and 16.6 +/- 1.6, respectively, when gadopentetate dimeglumine was given first. Results of quantitative evaluation showed increasing SNR and CNR with gadobenate dimeglumine in segments at progressively lower levels of the aorta, but increases in SNR and CNR at the infrarenal aorta (48.3 vs 40.6 and 44.2 vs 36.4, respectively) were not significant (P = .05 for both). CONCLUSION: Gadobenate dimeglumine at a dose of 0.1 mmol/kg is comparable to gadopentetate dimeglumine at 0.2 mmol/kg for contrast-enhanced renal MR angiography.
Adult↗
Detectability of catheters on bedside chest radiographs: comparison between liquid crystal display and high-resolution cathode-ray tube monitors.
PURPOSE: To compare observer performance with a flat-panel liquid crystal display (LCD) monitor and with a high-resolution gray-scale cathode-ray tube (CRT) monitor in the detection of simulated support catheters on bedside chest radiographs. MATERIALS AND METHODS: The ethics committee did not require approval or patient informed consent when this study began. Because of a change in regulations, before images were acquired the nature of the study and procedures were explained to patients or their relatives, and consent was then obtained. A total of 131 catheter fragments (12-14 per radiograph) were superimposed over 10 anteroposterior bedside chest radiographs obtained with storage phosphor technology. Images were displayed on an LCD monitor (1536 x 2048 matrix) and a CRT monitor (2048 x 2560 matrix). Five radiologists independently located the catheter fragments and rated their confidence in detection with bright and subdued ambient light. A two-way analysis of variance and the Friedman test were used for statistical analysis. RESULTS: There was no significant difference for either display type with respect to correctly detected catheter fragments (mean sensitivity, 56.6% and 56.0% for the CRT and the LCD monitors, respectively, with bright light and 61.2% for both monitors with subdued light). With both display types, detection rate with bright light decreased significantly (P < .05). False-positive rates and confidence ratings were not significantly affected by monitor type or ambient light. CONCLUSION: In a study with simulation of clinical conditions, performance of the LCD monitor and high-resolution CRT monitor for detection of support catheters on bedside chest radiographs was equivalent. With both displays, detection performance was equally reduced with bright ambient light.
Aged↗
Comparison of liquid crystal versus cathode ray tube display for the detection of simulated chest lesions.
The purpose of the study was to compare the detection performance of a cathode ray tube (CRT) monitor versus a liquid crystal display (LCD) monitor for simulated subtle pulmonary lesions. Ten templates containing simulated lung lesions were superimposed on an anthropomorphic chest phantom. Posteroanterior radiographs were obtained using flat panel technology and were displayed on a CRT and an LCD monitor. Image processing and reading conditions were equivalent for both softcopy displays. Five observers assessed lesion detectability using receiver-operating characteristic (ROC) methodology. A multivariate test (Pillai trace) was used to test the significance of differences (P<0.05). The multivariate test revealed significantly different detection rates for the lesion types, but no significant difference between the two display modes. Detection performance for both monitors was higher for nodules and micro-nodules and lower for lines and patchy opacities. Analysis of lesion subgroups according to their location in lucent/obscured lung areas was also not statistically significant. Under ideal reading conditions, CRT and LCD displays perform equivalently for the detection of simulated subtle pulmonary lesions.
Data Display↗
In vivo 3D analysis of the adipose tissue in the orbital apex and the compartments of the parasellar region.
As tissue dissections carried out on formaldehyde-fixed anatomical specimens demonstrate, the parasellar region (PSR), traditionally referred to as the cavernous sinus, is composed of three distinct compartments: orbital, pterygopalatine, and lateral sellar. The aim of our study was to identify and measure these compartments in the living and to describe the topography of their adipose body tissues. For this purpose data sets of 35 patients, who had undergone thin-section multislice computed tomography (CT), were examined using 3D-reconstruction software. The pterygopalatine and orbital compartments of the PSR could be identified in the images by their adipose bodies. We provide more exacting measurements of their size than have been presented in earlier studies. Furthermore, we include data about the uni- and bilateral presence of the single compartments and analyze the topography of the adipose tissue bodies in the orbital apex region. Our quantitative data and topographical descriptions confirm the compartmentalization concept of the PSR, allow for correct interpretation of CT scans of the orbital apex and anterior PSR, and provide baseline information for individual planning of surgical and radiological interventions.
Adipose Tissue↗
Comparison of an automatic versus a semiautomatic mode for gray-scale adaptation for digital chest radiography.
PURPOSE: To compare image quality of digital chest radiographs using 2 modes of gradation adjustment. METHODS: We compared image quality and visualization of anatomic landmarks of 50 chest radiographs after digital processing using a semiautomatic mode with a fixed gamma of 2.6 and an automatic mode with individual gamma adaptation. RESULTS: The mean gamma was significantly higher (P < 0.001) with the automatic mode (3.0 vs. 2.6, respectively). Patient constitution had no impact on the automatically adapted gamma for PA but showed a significant correlation (P < 0.001) for lateral images. For PA, there was a preference (P < 0.016) of the semiautomatic mode in heavier patients whereas no difference was seen in slim patients. For the lateral projection, there was a general preference (P = 0.001) of the automatic mode. CONCLUSION: For PA radiographs, the semiautomatic mode provides superior results for heavier patients without compromising the quality in slim patients. For lateral radiographs, the automatic mode provides generally superior results.
Adult↗
Skeletal applications for flat-panel versus storage-phosphor radiography: effect of exposure on detection of low-contrast details.
PURPOSE: To compare exposure requirements for similar detection performance with flat-panel detectors and the most recent generation of storage-phosphor plates in the simulated scatter of typical skeletal radiographic examinations. MATERIALS AND METHODS: A contrast-detail test object was covered with varying thicknesses of acrylic to simulate skeletal exposure conditions in the wrist, knee, and pelvis. Three series were obtained with increasing thicknesses of a simulated soft-tissue layer (5, 10, and 20 cm) and increasing tube voltage (50, 70, and 90 kVp). A fourth series was obtained with exposure conditions adapted to the phantom instructions (75 kVp). Images were acquired with a flat-panel detector (cesium iodide scintillator) and storage-phosphor plates at five exposure levels (speed class range, 100-1,600). Five readers evaluated 84 images to determine the threshold contrast of 12 lesion diameters (range, 0.25-11.1 mm). Statistical significance of differences between the two digital systems was assessed with two-way analysis of variance. RESULTS: A linear relationship was found between the number of detected lesions and the logarithm of exposure (R(2) > 0.98 for all series). On average, the flat-panel system required 45% less exposure than did the phosphor plates when 20-cm-thick acrylic was superimposed on the test object. Differences in exposure requirements were smaller with decreasing thicknesses of simulated soft-tissue layers and lower tube voltages (39% at 10 cm and 70 kVp, and 17% at 5 cm and 50 kVp). All differences were statistically significant. CONCLUSION: Flat-panel radiography provides improved contrast detectability and a potential for exposure reduction compared with those with storage-phosphor radiography. The best performance was achieved with conditions comparable to those for radiography of the trunk and lowest for conditions that simulate radiography of the extremities.
Bone and Bones↗
Misdiagnosis of pulmonary embolism in patients with allergic reaction--the importance of prior probability of disease.
Because pulmonary embolism (PE) and its treatment carry substantial risk of morbidity and mortality, accurate diagnosis is essential. We report two cases with allergic reactions, in which PE was suggested by routine ECG and D-dimer elevation and strengthened by spiral CT. Therapy with low-molecular-weight heparin was initiated and long-term anticoagulation was considered. As their histories did not reveal any predisposing factor to PE, the cases were re-evaluated. Elevation of D-dimer was now attributed to allergic reaction, ECG abnormalities were considered as constitutional, and findings from spiral CT attributed to breathing artifacts and partial-volume effects. The diagnosis of PE was therefore rejected and anticoagulant treatment discontinued without sequelae. These cases show the importance of determining clinical probability before ordering further diagnostic tests and critical interpretation of test results suggestive of PE, based on prior probability of the disease.
Adult↗
Alveolar recruitment of atelectasis under combined high-frequency jet ventilation: a computed tomography study.
OBJECTIVE: To quantify the effect of superimposed high-frequency jet ventilation on lung recruitment in adult patients with acute lung injury. DESIGN AND SETTING: Prospective clinical study in the intensive care unit of a university teaching hospital. PATIENTS: Eight adults suffering from acute lung injury with a mean lung injury score of 2.6+/-0.6 and pronounced atelectasis in at least two lung quadrants. The cause was either pneumonia ( n=5) or postoperative sepsis ( n=3). INTERVENTIONS: Superimposed high-frequency jet ventilation was initiated in patients following a mean of 4.4+/-1.7 days of conventional ventilation. Before and 4 h after the start of superimposed high-frequency jet ventilation differential lung volumes were determined by volumetry using computed tomography. MEASUREMENTS AND RESULTS: Superimposed high-frequency jet ventilation significantly increased the lung volume of every patient due to alveolar recruitment. This was achieved despite lower peak inspiratory pressures and higher PaO(2)/FIO(2) ratios than with conventional ventilation. CONCLUSIONS: Treatment with superimposed high-frequency jet ventilation for 4 h resulted in rapid alveolar recruitment in dependent lung areas, improved gas exchange, and better arterial oxygenation. It offers an effective and advantageous alternative to conventional ventilation for ventilatory management of respiratory insufficient patients.
Adult↗
Diagnostic management of patients with SAPHO syndrome: use of MR imaging to guide bone biopsy at CT for microbiological and histological work-up.
Propionibacterium acnes (P. acnes) is suspected to be involved in the pathophysiology of SAPHO syndrome, since it has been isolated repeatedly through open surgical bone biopsy. This study demonstrates the role of MRI in identifying inflamed bone areas in patients with SAPHO syndrome and the role of CT-guided bone biopsies in obtaining samples from these areas for microbiological and histopathological investigations, thus obviating open surgery. Fourteen consecutive patients with SAPHO syndrome were investigated by MRI to identify acute inflammatory changes in hyperostotic periarticular bone. The CT-guided biopsies for microbiological investigations were taken from the areas identified. Patients positive for P. acnes were started on long-term antibiotic therapy according to antibiotic susceptibility. On MRI the inflammatory changes appeared as hyperintense areas on fat-saturated T2 fast-spin-echo (FSE) images and showed signal increase on fat-saturated T1 SE images after Gd-DTPA. With MR localization CT-guided bone biopsies yielded P. acnes in 8 patients. No bacteria could be isolated from the remaining 6 patients. Acute inflammatory bone changes in SAPHO syndrome are well localized by MRI. With MR localization, CT-guided bone biopsies offer a minimally invasive alternative to open surgery in the detection of. P. acnes leading to the institution of a specific antibiotic therapy.
Acquired Hyperostosis Syndrome↗
Multislice CT: technical principles and future trends.
Multislice scanning has substantially improved the performance of CT scanners, and thus the relation between scan duration, available scan length, and spatial resolution along the patient axis (z-axis). Near-isotropic imaging of whole organ systems is already possible with 4-slice scanners, but only with 8- to 16-slice scanners can the scan duration be shortened as well. Reconstructing overlapping thin-section data ("secondary raw data set") provides the basis for image reconstruction in any desired plane. By using thick multiplanar reformation (MPR) techniques, image quality can be improved while keeping patient dose low. Using unfavorable scanning parameters, exposure dose can be substantially increased compared with single-slice scanning, but thick MPR and individual-dose modulation techniques can provide the basis for dose reduction. Low-kVp scanning, in particular, is useful in children and slim adults and is an excellent technique to improve image contrast in CT angiographic studies. Short spiral scans should be avoided with multislice CT since overranging (extra rotations at the beginning and end of the scan, used for data interpolation) can substantially increase patient dose. Future trends include the introduction of thinner detector rows, wider detector arrays, faster tube rotation, and area detectors than can also be used for fluoroscopy. Noise-reduction techniques and individual dose modulation will gain importance with higher isotropic resolution. Functional and perfusion imaging, as well as advanced image processing and computer-aided diagnosis programs, will add to the possibilities of the next generation of multislice CT scanners.
Forecasting↗
General principles of MDCT.
Multidetector CT (MDCT, multislice CT, multidetector-row CT, multisection CT) represents a breakthrough in CT technology. It has transformed CT from an transaxial cross-sectional technique into a true 3D imaging modality that allows for arbitrary cut planes as well as excellent 3D displays of the data volume. Multislice CT scanners provide a huge gain in performance that can be used to reduce scan time, to reduce section collimation, or to increase scan length substantially. The following article will provide an overview of the principles of multislice CT scanning. It describes the various detector systems and gives an introduction to the most important acquisition and reconstruction parameters. The article describes how reconstruction of thick multiplanar reformations can be used to take advantage of the 3D capabilities of multislice CT while keep radiation exposure to a minimum.
Humans↗
Digital radiography of the chest: detector techniques and performance parameters.
Substantial advances in detector technology characterize digital chest radiography. This article compares the various systems from a radiologist's point of view. Computed radiography (CR) is a well-established system that is robust, has good reproducibility, and is relatively inexpensive. Image quality has been continuously improved in recent years while the physical size of the readout units has been reduced and the throughput increased. CR is the only digital system that can be used for bedside chest radiographs. Improved detector properties and dual reading have made it a dose-efficient system. Although now widely available, a 4K image matrix does not appear to offer a general diagnostic improvement for imaging the chest. New developments with respect to detector composition and readout process can be expected in the future. Direct radiography (DR) is the common name for different technologies that are characterized by a direct readout matrix that covers the whole exposure area. Conversion of x-ray intensity into electric signals can either be direct (selenium-based systems) or indirect (scintillator/photodiode systems). Advantages of DR systems are a high image quality and the potential for dose reduction. The role of selenium radiography (Thoravision) has decreased after the advent of DR systems although this dedicated chest unit offers high image quality at 400 speed acquisition dose. Especially in a PACS environment, CR and DR systems will increasingly substitute for conventional radiography with advantages for CR for bedside chest radiographs and for DR for high-end chest stands.
Humans↗
Principles of image processing in digital chest radiography.
Image processing has a major impact on image quality and diagnostic performance of digital chest radiographs. Goals of processing are to reduce the dynamic range of the image data to capture the full range of attenuation differences between lungs and mediastinum, to improve the modulation transfer function to optimize spatial resolution, to enhance structural contrast, and to suppress image noise. Image processing comprises look-up table operations and spatial filtering. Look-up table operations allow for automated signal normalization and arbitrary choice of image gradation. The most simple and still widely applied spatial filtering algorithms are based on unsharp masking. Various modifications were introduced for dynamic range reduction and MTF restoration. More elaborate and more effective are multi-scale frequency processing algorithms. They are based on the subdivision of an image in multiple frequency bands according to its structural composition. This allows for a wide range of image manipulations including a size-independent enhancement of low-contrast structures. Principles of the various algorithms will be explained and their impact on image appearance will be illustrated by clinical examples. Optimum and sub-optimum parameter settings are discussed and pitfalls will be explained.
Humans↗
US as a primary diagnostic tool in relation to negative appendectomy: six years experience.
PURPOSE: To evaluate the effect of ultrasonography (US) on the rate of appendectomy after false-positive diagnosis of acute appendicitis (negative appendectomy). MATERIALS AND METHODS: Data were analyzed in 736 pediatric patients (mean age, 13.2 years) who had undergone appendectomy between 1995 and 2000. Histologic data were compared in patients who underwent US with those who did not undergo imaging prior to surgery. US was performed by a radiologist or a pediatric surgeon or both. RESULTS: A total of 643 (87.4%) of the 736 pediatric patients underwent preoperative US, and 93 (12.6%) of the 736 did not undergo preoperative US. Of the 736 patients, 97 (13.2%) underwent negative appendectomy. Thirty-four (36.6%) of the 93 patients who underwent appendectomy with no preoperative US and 63 (9.8%) of the 643 patients who underwent preoperative US underwent negative appendectomy. There was a significant association between US and positive appendectomy (P <.001). CONCLUSION: US in pediatric patients suspected of having appendicitis can significantly lower the negative appendectomy rate.
Adolescent↗
Detection of monitoring materials on bedside chest radiographs with the most recent generation of storage phosphor plates: dose increase does not improve detection performance.
PURPOSE: To evaluate the performance of the most recent generation of storage phosphor plates for the detection of low-contrast catheter material on bedside chest radiographs. MATERIALS AND METHODS: In 10 patients in the intensive care unit, bedside chest radiographs were obtained with a 400-speed conventional screen-film system and with storage phosphor plates with exposure levels comparable to a 200-, 400-, or 800-speed conventional system. The chest radiograph was divided into 20 regions, 60% of which were superimposed with low-contrast catheter fragments. Six observers independently assessed the presence of catheter fragments by using a receiver operating characteristic (ROC) methodology. RESULTS: Detection performance (mean area under the ROC curve [Az]) with the storage phosphor plates was significantly superior to that with the screen-film system (Az = 0.76) at all three dose levels (Az = 0.88, 0.87, and 0.83 for 200-, 400-, and 800-speed doses, respectively; P <.05). Increasing the dose to a 200-speed system did not significantly increase detection performance compared with that with the 400-speed digital radiographs (Az = 0.88 vs 0.87). Dose reduction to 800 speed significantly deteriorated the detection performance (Az = 0.83) compared with that with the 400- and 200-speed digital radiographs, respectively. CONCLUSION: The most recent generation of storage phosphor plates is superior to a 400-speed screen-film system for the detection of catheter material, even at an exposure level of 800 speed.
Adult↗
Impact of ambient light and window settings on the detectability of catheters on soft-copy display of chest radiographs at bedside.
OBJECTIVE: The aim of this study was to evaluate how ambient light and interactive adjustment of density and contrast affect the detection of catheter fragments when interpreting bedside chest radiographs on soft-copy displays. MATERIALS AND METHODS: A total of 131 catheter fragments were superimposed over 10 bedside chest radiographs obtained with storage phosphor technology. Images were displayed on a clinical intensive care unit viewing station (color cathode-ray tube monitor, 21 inch [53 cm], 1280 x 1024 matrix) and were independently evaluated by five radiologists. The number of catheter fragments per image varied between 12 and 14, with an approximately equal distribution in high- and low-absorption areas. Detectability of catheter fragments was assessed under subdued and bright ambient light conditions with and without interactive adjustment of window width and level. RESULTS: Under subdued light, the detection rate of catheter fragments was significantly higher than under bright light (51.8% vs 56.6%, p < 0.05). Interactive window setting adjustment significantly increased the detection rate from 52.5% to 60.8% (p < 0.05) under subdued light and from 47.9% to 55.6% (p < 0.05) under bright light. With adjustment of window settings, the difference between the detection rates under subdued light (60.8%) and under bright light (55.6%) did not reach statistical significance. CONCLUSION: Detection of catheters on soft-copy display is significantly decreased by bright ambient light, an effect that can be largely compensated for by means of interactive adjustment of window settings.
Analysis of Variance↗
Posterior "Nutcracker" phenomenon in a patient with abdominal aortic aneurysm.
We report on a posterior "nutcracker" phenomenon due to an abdominal aortic aneurysm in a patient with a retro-aortic left renal vein. A 71-year-old man with a known abdominal aortic aneurysm presented in the emergency room with mild hematuria and flank pain. Computed tomography angiography revealed an aortic aneurysm, which compressed the left renal vein between the aorta and the vertebral column. Compression of the left renal vein, due to the aorta with consecutive congestion and hematuria as well as flank pain, was previously described as nutcracker phenomenon. In case of a retro-aortic left renal vein, increase of the aortic diameter can lead to compression of the renal vein and furthermore to the classical signs and symptoms of the "nutcracker" phenomenon, even though the aneurysm is not ruptured or there are no aorto-caval or aorto-left renal vein fistulas.
Aged↗