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Mathias Prokop

Publications and source records attributed to Mathias Prokop.

29 records · Page 2Linked to original sources
PubMed2003

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↗
PubMed2003

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↗
PubMed2003

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↗
PubMed2003

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↗
PubMed2003

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↗
PubMed2002

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↗
PubMed2002

Traumatic injuries: imaging and intervention of large arterial trauma.

Traumatic vessel injury can cause bleeding, thrombosis, embolization, or malperfusion due to external compression and spasm. Non-traumatic causes of acute large arterial emergencies include rupture of an aneurysm and pseudoaneurysm, dissection, embolization, and thrombosis in hypercoagulability syndromes. Ultrasonography is, of course, the imaging modality of choice in emergency cases; however, in central vascular injuries, spiral CT with contrast enhancement is the imaging modality that provides the most information. Angiography may be necessary for detailed information and before intervention. Stent-grafts are used to close large vascular lacerations, ruptured aortic aneurysms, and the entry tear of dissections. Interventional radiology methods play a major role in managing vascular emergencies.

Angiography↗
PubMed2002

Single- and multi-slice spiral computed tomography of the paediatric kidney.

Single- and multi-slice computed tomography (CT) is regarded as the primary imaging tool in traumatology, both in adults and children. For complicated infectious disease and renal tumours, these techniques are recommended only as secondary diagnostic tools. Specifically, multi-slice CT (MSCT) provides excellent spatial resolution, which is a particular advantage for the evaluation of small structures as they are typical in children. However, MSCT offers more information than is required for diagnosis. Therefore, low-dose protocols are necessary for paediatric examinations. The CT dose-index (CTDI(vol)) should not exceed 2 mGy for newborns, 4 mGy for toddlers, 5 mGy for elementary school children, and 8 mGy for adolescents.

Adolescent↗
PubMedDate not supplied

High-resolution CT and CT angiography of peripheral pulmonary vascular disorders.

Peripheral pulmonary vascular disorders that can be evaluated with computed tomography (CT) include various disease entities with overlapping imaging features and a wide range of clinical manifestations. The overall accuracy of CT in the diagnosis of pulmonary vascular disorders increases with improved spatial resolution, administration of a high-flow contrast material bolus, and the use of cardiac gating. The integration of high-resolution CT and CT angiographic techniques into one scanning protocol has important clinical implications for multisection CT and makes it the imaging modality of choice in the evaluation of this complex group of disorders.

Angiography↗
PubMedDate not supplied

Dedicated multidetector CT of the stomach: spectrum of diseases.

Multidetector computed tomography (CT) offers new opportunities in imaging of the gastrointestinal tract. When thin collimation is used, near-isotropic imaging of the stomach is possible, allowing high-quality multiplanar reformation and three-dimensional reconstruction of gastric images. Proper distention of the stomach and optimally timed administration of intravenous contrast material are required to detect and characterize disease. In contrast to gastroscopy and double-contrast studies of the stomach, CT provides information about both the gastric wall and the extragastric extent of disease. Preoperative staging of gastric carcinoma appears to be the main clinical indication for multidetector CT. In addition, multidetector CT allows detection of other gastric malignancies (lymphoma, carcinoid tumors, metastases, gastrointestinal stromal tumors) and benign gastric tumors (neural tumors, polyps). Gastric inflammation (gastritis, ulcers, Ménétrier disease) and miscellaneous gastric conditions (emphysema, gastric outlet obstruction, varices) can also be visualized with multidetector CT. Multidetector CT is a valuable tool for the evaluation of gastric wall disease and serves as an adjunct to endoscopy.

Diagnosis, Differential↗