Biomedical subjects

M Prokop

Publications and source records attributed to M Prokop.

At least 37 records · Page 2Linked to original sources

PubMed2000

Low-dose high-resolution CT of the petrous bone.

PURPOSE: To show that CT of the petrous bone can be realized using a low-dose technique. MATERIAL: and methods: A high-contrast phantom was scanned with 1.5 mm slice thickness and 60-510 mAs using the reconstruction algorithms standard, bone and edge. In 50 patients, the petrous bone was examined using the standard protocol at 510 mAS. Additionally, selected slices were made at 120 or 210 mAs. The resolution of relevant structures was compared. Phantom studies were repeated on a second CT-device; images of patients scanned with 80 mAs were analyzed in regard to resolution of osseous details. RESULTS: With the first CT-device structures of the phantom up to 0. 5 mm were depicted using 510 mAs and the edge kernel. With 120 mAs and the bone kernel structures of 0.6 mm could be distinguished. Although the same resolution was achieved with 60 mAs and the edge kernel, patient examinations showed a profound image noise. The results achieved with 120 mAs and the bone algorithm, however, were equal to that of 510 mAs. With the second device the same image quality was realized with only 80 mAs. CONCLUSION: CT-examinations of the petrous bone can be effected without loss of diagnostic information using only 15% of the radiation dose used for a standard brain examination.

Humans↗

PubMed1999

Unilateral osseous bridging between the arches of atlas and axis after trauma.

STUDY DESIGN: This is a case report. OBJECTIVE: To present a case of osseous bridging between C1 and C2 of posttraumatic origin and with an associated closed head injury and to discuss its pathogenesis and clinical outcome after surgical resection. SUMMARY OF BACKGROUND DATA: Heterotopic ossifications of posttraumatic origin in the spine are rare. To the authors' knowledge, no cases have been reported of spontaneous bony bridging between C1 and C2 with a posttraumatic origin. METHODS: Heterotopic ossifications were detected when pain and limited axial rotation (left/right 10 degrees/0 degree/20 degrees) were persistent, despite intensive physical therapy. Because heterotopic ossifications were ankylosing C1 and C2, the decision was to resect the osseous bridge in combination with a careful mobilization of the cervical spine. Functional computed tomography was performed for analysis of the postoperative results. RESULTS: Four months after surgery, clinical examination showed asymptomatic increased axial rotation. Functional computed tomography indicated that left C1-C2 axial rotation was reduced, possibly related to impingement caused by residual bony spurs. Pathologic changes in the surrounding soft tissue may be another important factor in the persistent limitation of rotation. CONCLUSIONS: Osseous bridging between C1 and C2 may be considered when persistent pain and limited axial rotation are observed after trauma. Operative resection, together with careful intraoperative and postoperative mobilization, may be the treatment of choice.

Abdominal Injuries↗

PubMed1999

[3-dimensional sonography for volume determination of liver tumors--report of initial experiences].

In a clinical trial the accuracy of volumetry by use of three-dimensional ultrasound (3-D-US) in comparison to three-dimensional computer tomography (3-D-CT) was evaluated. Overall, 42 patients with focal hepatic lesions were investigated with 2-D- and 3-D ultrasound. In 11 patients additional computerized tomographic arterial portography using spiral technique was performed. The volumes of the lesions were calculated using the ellipsoid formula (for 2-D- and 3-D-US) as well as with a planimetric reconstruction for 3-D-US and 3-D-CT. In addition the intra- and inter-investigator variability of 3-D ultrasound was determined. The volume of the investigated liver lesions (planimetric reconstruction with 3-D ultrasound) ranged between 1.5 cm3 and 1231 cm3 with a mean volume of 155 cm3 and a median volume of 68 cm3. The deviation of 2-D-US vs 3-D-CT was -62% to +68%, in the case of 3-D-US (ellipsoid) vs 3-D-CT it was -28% to +9%, and for 3-D-US (planimetry) vs 3-D-CT it was -21% to +9%. The concordance index kappa was 0.886, showing very good agreement between the two investigators. The intra-investigator variability was 5%. Our data show that volume measurement by use of 3-D-US in independent of the investigator. With regard to accuracy of volume measurements 3-D-US is comparable to 3-D-CT but more precise than 2-D-US. These results indicate that 3-D-US may be applied in the follow-up of tumor patients as an alternative diagnostic procedure to computer tomography. In addition 3-D-US might be useful in planning liver resections by virtue of better evaluation of the volume of the liver tissue remaining after resection and better visualization of the topography of liver tumors and major hepatic vessels.

Artificial Intelligence↗

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↗

PubMed1999

[Atypical gallstone ileus: radiologic and sonographic findings].

We report on a case of an atypically located gallstone ileus as a rare complication of cholecystolithiasis. A 61-year old lady with a history of diabetes type II and nephrolitiasis presented with abdominal pain lasting for 8 days and with vomiting and diarrhoea. Physical examination revealed a palpable tumour and pain in the left lower abdomen. An extensive elevation of blood sugar, CRP and leukocytosis was found. Initially X-ray of the abdomen and sonography showed signs of a subileus. Additionally a 5 x 2 cm mass with dorsal shadowing was detected by ultrasound. Gallbladder and the biliary system were normal. The sonographic suspicion of a gallstone ileus was confirmed by a subsequent CT scan. Under operation the gallstone was found in the distal Jejunum. A gallstone ileus must be included in the differential diagnosis of a tumour in the left lower abdomen. A tumour with dorsal shadowing and signs of a subileus may be the only sonographic findings of a gallstone ileus.

Cholelithiasis↗

PubMed1999

Protocols and future directions in imaging of renal artery stenosis: CT angiography.

Computed tomographic angiography (CTA) has become an established technique for minimally invasive imaging of renal artery stenosis. This article describes in detail the current scan protocols suggested for renal artery stenosis and explains the rationale behind the choice of such parameters as collimation, pitch, reconstruction interval, scan duration and scan length. It discusses the optimized use of contrast agents including bolus triggering and a saline flush to improve contrast agent utilization. Examples of optimized scan protocols are given for various scanner types including subsecond scanners and multislice computed tomography. With standard 1-s scanners, a slice collimation of 2 mm is recommended. A pitch factor of 1.5-2 is important for optimum volume coverage. Smoothing reconstruction kernels improve signal-to-noise ratio and allow for dose reduction. For optimum results, the plateau phase of contrast enhancement has to be matched as precisely as possible. Thus, a test bolus injection or an automated bolus triggering technique should be employed. Axial CT images remain the basis for making the diagnosis but require interactive viewing on a monitor display. Image processing (multiplanar reformats; maximum intensity projections; shaded surface displays) is employed to display the renal arteries. Given optimized examination protocols, high sensitivity and specificity can be achieved (90-98%) with negative predictive values of greater than 95%. Thus, a normal CT angiogram virtually rules out renal artery stenosis.

Angiography↗

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↗