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M Prokop

Publications and source records attributed to M Prokop.

At least 19 recordsLinked to original sources
PubMed1999

[The value of CT in classification and decision making in acetabulum fractures. A systematic analysis].

UNLABELLED: The classification of acetabular fractures and especially the diagnosis of additional lesions can be misleading, when the personal experience is limited and the decisions are based only on conventional radiographs. The introduction of Spiral-CT with multiplanar reformations and 3-D views has improved the quality of visualization. Due to their higher costs, the need of these additional diagnostic tools is frequently questioned. This paper discusses the relevance of plain radiographs, 2-D-CTs, 3-D-CTs and Femursubtraction-CTs (FsCT) for the classification of acetabular fractures, based on a controlled study. METHODS: Thirty physicians with different levels of experience in acetabular surgery were divided in three groups of 10 each: group I comprised residents without operative experience in acetabular surgery, group II was physicians with 3-10 years of operative experience, and group III was experts in acetabular surgery. A total of 10 complete radiographic cases of high quality providing all levels of preoperative diagnostics (plain radiographs, 2-D-CT, CT with multiplanar reformation, 3-D-CT, Fs-CT) of different acetabular fracture types were prepared. The task for each candidate was to classify the fracture according to Letournel and to identify all additional injuries within the hip joint (e.g. marginal impaction, head fractures, etc.). The different diagnostic "levels" could be ordered stepwise according to personal need and no time limit was given. The case was finished when the candidate presented his final diagnosis. The use of the different radiographs, the preliminary diagnosis, the changes in diagnosis, and the final decisions were recorded. These findings were correlated with the different levels of experience and against a "consensus classification" which was generated by thorough discussion, and the use of intraoperative information and postoperative radiographs not accessible to the candidates. RESULTS: The "correct" fracture classification based on plain radiographs was: group I, 11%; group II, 32%; group III, 61%. Based on 2-D-CT a "correct" diagnosis was reached by 30% in group I, by 55% in group II, and by 76% in group III. With consideration of the "transient forms" in acetabular fractures based on Letournel and the 3-D-CT used mainly by group I, the rate of "correct" classifications rose to 65% in group I, 64% in group II and 83% in group III. The modifiers were diagnosed "correctly" in group I by 37%, in group II by 56%, and in group III by 73%. The use of the 3-D-CT and especially the Fs-CT by group I resulted in an improvement in the rate of correct classifications to 61%, whereas in group II the Fs-Ct was used only exceptionally. The 2-D-CT was the basis for the diagnosis of the additional lesions in acetabular fractures within all groups resulting in 73% complete diagnoses in group III. This study showed the importance of CT for the exact analysis and classification of acetabular fractures. In particular, the secondary reformations in CT and the 3-D-views dramatically improved the rate of "correct" classifications in the group of surgeons with limited personal experience in acetabular surgery. This allows the less experienced an acceptable level of "correct" diagnoses, so that the treatment options can be weighed correctly. Among the "experts" a rate of divergent classifications of approximately 20% was observed, especially in "transient" forms of acetabular fractures.

Acetabulum↗
PubMed1998

Volume measurements of localized hepatic lesions using three-dimensional sonography in comparison with three-dimensional computed tomography.

Three-dimensional (3D) sonography represents a further development of non-invasive, diagnostic sonographic imaging techniques. The clinical use of this technique in the hepatobiliary system reveals its possible applications, especially in the case of localized lesions. The goal of this study was to evaluate the accuracy of in vivo, three-dimensional ultrasonography with a freely moveable transducer as compared with a computerized tomographic arterial portography using the spiral technique (S-CTAP). A total of 42 patients with localized hepatic lesions (1.5 to 1231 cm3, mean 155 cm3) standard deviation (SD) 231 cm3 were examined using conventional (2D) and 3D ultrasonography (US). Eleven of these patients additionally underwent spiral CTAP. The volumes were calculated using the ellipsoid formula (2D US and 3D US) and were also reconstructed planimetrically with the aid of work stations (3D US and 3D CT). Furthermore, the intra and inter-investigator variability of the 3D planimetry was determined. The conformity of US methods with those using S-CTAP was determined with Bland and Altman s limits of agreement. Inter-rater agreement was calculated using Cohen s concordance index kappa. The deviation of 2D US from 3D CT was -62% to +68% and that of 3D US (ellipsoid) from 3D CT was -28% to +9%. Between 3D US (planimetry) and S-CTAP the deviation was -21% to 9%. The kappa value was 0.886. The intra-investigator variability was 5%. Our results show that the planimetric 3D US is independent of the investigator and, with regard to the volume determinations, is substantially more accurate than measurements with conventional sonography and comparable with those measurements made using CT investigations. 3D sonography may be applied complementarily to CT as an economical procedure for the follow-up of tumor disease.

Adult↗
PubMed1998

CT and MR to assess the response of liver tumors to hepatic perfusion.

Assessment of the response of liver tumors to hepatic perfusion is strongly based on cross-sectional imaging. CT and MRI have gained considerably in diagnostic accuracy with the introduction of new, fast acquisition techniques such as spiral CT or breath-hold techniques in MRI. In addition, the administration of contrast agents has improved and has led to new injection protocols in spiral CT and the development of liver-specific contrast agents in MRI. Imaging techniques, however, strongly rely on changes in morphology such as size, vascularization and signs of necrosis. Functional signs of tumor metabolism cannot be visualized directly. While most functional imaging techniques at present are based on nuclear medicine, MR spectroscopy (MRS) offers the potential to assess tumor metabolism. Its promise is a direct match between the morphologic information of MRI and the metabolic information provided by MRS. The application of MRS to the liver, however, is still in this infancy. This article will give an overview of the multitude of CT and MR techniques that can be used to monitor tumor response. It will discuss the various signs of tumor regression and some typical complications of hepatic perfusion therapy. In particular, the influence of tumor characteristics-tics on the optimum choice of imaging technique will be demonstrated.

Chemotherapy, Cancer, Regional Perfusion↗
PubMed1998

Increasing spiral CT benefits with postprocessing applications.

This paper reviews the current and future role of various postprocessing tools for epidemiologically important diseases. It introduces a generic business system for diagnosis and treatment using Spiral CT. Postprocessing of Spiral CT data should become a routine part of radiological practice. As viewing moves from film to monitor displays, interactive postprocessing tools support evaluation of CT studies and will in some cases also improve diagnostic accuracy. Track-ball controlled browsing through the volume data may be performed on axial images or on multiplanar reformats (MPR). These tools can be expected to become an integral part of most CT evaluations in the near future. Already now, MPR are important adjuncts for most orthopaedic applications. Presently, three-dimensional (3D) displays are used mainly in orthopaedic and trauma patients. In CT angiography, 3D surface displays and maximum intensity projections are routine display modalities. New volume rendering techniques (VRT) with interactive parameter changes will make 3D imaging of soft tissues feasible as well. The key input factor for many postprocessing applications will be Spiral CT data sets with high z-axis resolution (subsecond scanning, thin collimation, overlapping image reconstruction) and optimised application of contrast media. The most important benefit of postprocessing is the communication with the referring physician since 3D representations are becoming increasingly important for treatment planning and control. Postprocessing services will become a key ingredient of a successful radiological practice. If radiology does not provide it, the other physicians will do it themselves. For treatment simulation, virtual surgical instruments and tissue motion models are still in their infancy and will keep software architects and physicians busy for the next decade of Spiral-CT.

Humans↗
PubMed1998

[Window width as a dosage-relevant factor in high-contrast structures in CT].

PURPOSE: To establish the relationship between window width and dose to be applied in low-dose high-resolution (HR) computed tomography (CT). MATERIAL AND METHODS: Low-dose HR CT-scans of the petrous bone displayed with different window values were analyzed for identification of osseous details. For two homogeneous phantoms, standard deviation of CT-numbers were measured in order to calculate the fraction of pixels not displayed within the correct grey level. RESULTS: The broadest window used (4000 HU) allowed the best distinction of osseous structures. Standard deviation of CT-numbers in the phantoms varied between 28.5 and 43.2 (mean = 33.6) HU. Thus, only 26.6% of all pixels are displayed in the correct grey level for a 1000 HU-window, but 82.3% for a 4000 HU-window. CONCLUSION: When using low doses and HR-reconstruction algorithms, large window widths allow for an optimal assessment of high-contrast structures. Under these conditions, even high standard deviations of the CT-numbers will not compromise image evaluation. Due to the restricted number of grey-levels that can be distinguished by the human eye, image noise is compressed into a smaller number of discernable grey-levels. Because of the inverse square root function between dose to be applied and window width used (derived in the article), an even minor enlargement of window permits considerable reductions of patient exposure while the discernable image noise remains constant.

Artifacts↗
PubMed1998

Computational site-directed mutagenesis of haloalkane dehalogenase in position 172.

The application of molecular modelling and quantum-chemistry calculations for the 'computational site-directed mutagenesis' of haloalkane dehalogenase is described here. The exhaustive set of single point mutants of haloalkane dehalogenase in position 172 was constructed by homology modelling. The ability of substituting residues to stabilize the halide ion formed during the dehalogenation reaction in the enzyme active site was probed by quantum-chemical calculations. A simplified modelling procedure was adopted to obtain informative results on the potential activity of mutant proteins in a sufficiently short period of time, which, in the future, could be applicable for making bona fide predictions of mutants' activity prior to their preparation in the laboratory. The reaction pathways for the carbon-halide bond cleavage were calculated using microscopic models of wild type and mutant proteins. The theoretical parameters derived from the calculation, i.e. relative energies and selected atomic charges of educt, product and transition state structures, were statistically correlated with experimentally determined activities. The charge difference of educt and product on the halide-stabilizing hydrogen atom of residue 172 was the best parameter to distinguish protein variants with high activity from mutant proteins displaying a low activity. All mutants with significant activity in the experiment were found to have this parameter one order of magnitude higher than mutants with low activity. The results obtained are discussed in the light of the practical application of this methodology for the prediction of potentially active protein variants. Further automation of the modelling procedure is suggested for combinatorial screening of the large number of protein variants. Coupling of the dehalogenation reaction with hydrogenation of the halide ion formed during the reaction in the enzyme active site was proposed as a possible way to improve the catalytic activity of the haloalkane dehalogenase of Xanthobacter autotrophicus GJ10.

Amino Acid Substitution↗
PubMed1998

Two-step procedure in Budd-Chiari syndrome with severe intrahepatic vena cava stenosis: vena cava stenting and portocaval shunt.

Budd-Chiari syndrome is characterized by hepatic venous outflow obstruction, which often leads to death as a result of portal hypertension and liver failure. Venous decompressive shunt surgery and liver transplantation represent efficient surgical treatments of Budd-Chiari syndrome. In the case presented here, severe intrahepatic compression of the inferior vena cava (IVC) was caused by the hypertrophic caudate lobe. A mere portocaval shunt was not feasible because of a large pressure gradient across the intrahepatic stenosis. A two-step procedure with preoperative radiological dilation and stenting of the intrahepatic IVC followed by a portocaval shunt was successfully performed. Consequently, liver transplantation and its subsequent immunosuppression could be avoided.

Adult↗
PubMed1998

[Volumetry of circumscribed liver changes with 3-D ultrasound in comparison with 3-D computerized tomography].

The accuracy of volume measurement using three-dimensional ultrasound (3D-US) in comparison to three-dimensional computer tomography (3D-CT) was evaluated in 11 patients. The deviation of tumor volumes measured with 3D-US (ellipsoid formula) from 3D-CT was -28% to +9% and for 3D-US (planimetry reconstruction) from 3D-CT was -21% to +9%. These data show that volume measurement using 3D-US provides comparable results to 3D-CT. Clinically, 3D-US could be helpful in the follow-up of patients with non-resectable tumors or in planning liver resections by assessing the volume of liver tissue remaining after resection or by a better visualization of the topography of liver tumors and major hepatic structures.

Follow-Up Studies↗
PubMed1997

Storage phosphor radiography

LANGUAGE="EN">Summary. Storage phosphor radiography is a digital technique that uses photo-stimulable phosphor screens to substitute for conventional screen-film combinations. While the technique is more than 15 years old, it is only recently that technological and economic aspects of these systems have become favourable enough to envisage a more widespread clinical application.

Journal Article↗
PubMed1997

Digital image processing

LANGUAGE="EN">Summary. The image quality of a radiograph is determined by the local contrast, spatial resolution, latitude and the image noise. The goal of digital processing is to improve the visualisation of pathology by optimising these physical parameters. Processing parameters need to be chosen correctly in order to overcome the inverse relationship between contrast and latitude while producing images that retain a conventional appearance. Unsharp mask filtering (UMF) is a simple technique for improving image quality. This technique, however, suffers from serious drawbacks, such as the suppression of pathologic lesions or artifacts that may simulate pathology. Manufacturers have developed different approaches in order to overcome problems and artifacts derived from this technique.

Journal Article↗
PubMed1997

MRI contrast media - new developments and trends. CTA vs. MRA.

Recent developments in the non-invasive techniques of magnetic resonance angiography (MRA) and computerised tomographic angiography (CTA) are challenging conventional catheter angiography. Current indications for both techniques are discussed, such as their ability to diagnose aortic, pulmonary, renal, carotid and peripheral vascular diseases. Both tools provide almost identical clinical results, although each has their own advantages and disadvantages. MRA should be the technique of choice in young patients or those with real impairment since the gadolinium-based contrast agents are non-ionising and do not cause nephrotoxicity. On the other hand, MRA examination times are longer than those typically required for CTA, and therefore MRA is less suited to examinations of acute conditions.

Angiography↗
PubMed1997

Accuracy of single-energy quantitative computed tomography in the assessment of bone mineral density of cervical vertebrae.

Earlier studies have shown that single-energy quantitative computed tomography (SEQCT) is a reliable method for bone mineral density (BMD) measurements in thoracic and lumbar vertebrae. Moreover, SEQCT has proved to be a useful parameter in the selection of appropriate implants in cervical spondylodesis. The aim of this study was to determine the accuracy of SEQCT in cervical vertebrae BMD measurement. BMD with reference to calcium hydroxyapatite (Ca10[PO4]6[OH]2) was assessed by SEQCT in 100 human vertebral bodies of the cervical spine. Bone cylinders were then cut from the appropriate region of interest. The cylinder volume was determined by the liquid displacement technique. The density of the mineral component was measured following incineration at 1100 degrees C for 24 h. The calculated BMD was correlated with the SEQCT values, resulting in a coefficient of r = 0.79 (P < 0.01). Mean SEQCT values were significantly lower than those determined by direct density assessment (t-test for coupled sampling, P < 0.02). This result was in agreement with studies on thoracic and lumbar vertebrae. These data suggest that SEQCT can reliably measure BMD in the cervical spine.

Bone Density↗
PubMed1997

[Evaluation of congenital vena cava anomalies and acquired vena cava obstructions after atrial switch operation using spiral computerized tomography and 3-dimensional reconstruction].

We report spiral-CT findings in adult patients with congenital abnormalities of the vena cava and systemic venous obstructions after atrial switch operation. Especially systemic venous obstruction is a well-known complication following Mustard procedure for transposition of the great arteries. The results demonstrate that computed tomography, particularly with the use of 3-dimensional surface reconstruction, is very useful as a highly sensitive procedure for the detailed depiction of abnormalities of the vena cava or of residua and sequelae after inflow correction for complete transposition. Demonstration of such abnormalities or obstructions after atrial switch operation is important, since the recognition and quantitation of caval anomalies by clinical techniques is unreliable and indeed often impossible. Imaging procedures such as spiral computed tomography are important for this purpose. Advantages of spiral computed tomography, particularly with 3-dimensional reconstruction, are discussed.

Adolescent↗
PubMed1997

Storage phosphor radiography.

Storage phosphor radiography is a digital technique that uses photo-stimulable, phosphor screens to substitute for conventional screen-film combinations. While the technique is more than 15 years old, it is only recently that technological and economic aspects of these systems have become favourable enough to envisage a more widespread clinical application.

Equipment Design↗
PubMed1997

Digital image processing.

The image quality of a radiograph is determined by the local contrast, spatial resolution, latitude and the image noise. The goal of digital processing is to improve the visualisation of pathology by optimising these physical parameters. Processing parameters need to be chosen correctly in order to overcome the inverse relationship between contrast and latitude while producing images that retain a conventional appearance. Unsharp mask filtering (UMF) is a simple technique for improving image quality. This technique, however, suffers from serious drawbacks, such as the suppression of pathologic lesions or artifacts that may simulate pathology. Manufacturers have developed different approaches in order to overcome problems and artifacts derived from this technique.

Artifacts↗
PubMed1996

[Spiral CT of the lung. Technique, findings, value].

Spiral CT allows for examination of the whole chest within a single breathhold. As compared to standard CT, spiral CT has an increased sensitivity for the detection of pulmonary nodules, of small mediastinal and bronchopulmonary lymph nodes, and of pleural plaques improves characterization of lesion morphology. New diagnostic applications include the detection of very subtle diffuse lung disease and the diagnosis of pulmonary embolism and vascular malformations. For the diagnosis of tracheobronchial pathology, spiral CT is an ideal supplement to bronchoscopy.

Bronchial Diseases↗
PubMed1996

Selenium radiography versus storage phosphor and conventional radiography in the detection of simulated chest lesions.

PURPOSE: To compare selenium detectors with three conventional and digital detector systems for the detection of simulated pulmonary lesions. MATERIALS AND METHODS: Templates containing nodules, linear structures, and micronodular opacities were superimposed over an anthropomorphic chest phantom. The authors compared lesion detection with use of storage phosphor radiography (250 speed), selenium radiography (250 speed) with an antiscatter grid, selenium radiography (450 speed) without an antiscatter grid, an asymmetric screen-film system (400 speed), and a conventional screen-film system (250 speed). Detection performance of 10 radiologists was compared by using a multireader-multicase receiver operating characteristic analysis of variance. RESULTS: For the detection of nodules, no statistically significant differences between imaging modes were seen. For the detection of micronodules and linear lesions, both selenium techniques were superior to all other modes (P < .05). In addition, the asymmetric screen-film radiographs were inferior (P < .05) to the conventional screen-film radiographs and to storage phosphor radiographs for the detection of micronodules. CONCLUSION: The selenium detector improves detection of simulated fine linear and low-contrast micronodular details and appears to be superior to other detector systems for chest radiography.

Humans↗