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Biomedical subjects

K J Lehmann

Publications and source records attributed to K J Lehmann.

13 recordsLinked to original sources
PubMed1992

[Thoracic radiographs with the AMBER system. A comparison of the diagnostic image quality of film-screen and storage-phosphor radiographs on the grid-partition stand and the AMBER system].

Since April 1990, chest radiographs in the Mannheim clinic have been performed with a slit technique (Kodak AMBER System). In this study, image quality from conventional film/screen combination and from storage phosphor radiography was compared with that from the AMBER system. Phantoms were used to measure spatial resolution and to determine the detectability of nodules. Image quality affecting various structures within the thorax was evaluated on 200 p.a. and 48 lateral radiographs by three radiologists from Mannheim and four from Berlin. In the retrocardiac, retrodiaphragmatic, mediastinal and peripheral portions the best image quality was obtained by film/screen with the AMBER system. Compared with conventional film/screen images, there was no improvement from the AMBER system within the lung parenchyma. The use of storage phosphor plates with the AMBER system did not lead to any further improvement in image quality.

Evaluation Studies as Topic↗
PubMed1992

[Do the obstetrically relevant bony pelvic measurements change? A retrospective analysis of computed tomographic pelvic x-rays].

The important dimensions of pelvimetry were evaluated from 467 CT studies of the pelvis by trigonometric deduction. The age of the women was between 18 and 88 years. In addition to the diameters, which are routinely used for pelvimetry, transverse and sagittal diameters, pelvic angles and areas of pelvic planes were calculated. On condition that the pelvic dimensions do not depend on age the parameters can be regarded as representative of sexual maturity. 5 parameters showed highly significant and 7 parameters showed significant differences between the age-classes 1901-1920 and 1950-1971. An increase of pelvic dimensions (1950-1971) was found at the planes of the pelvic inlet and outlet in contrast to the dimensions of the pelvic center. The results confirm the importance of the bispinous diameter for pelvimetry as well as the demand for a revision of the standard values of the first half of the century.

Adolescent↗
PubMed1992

[Magnetic resonance tomography as the basis for biomechanical analysis. The simulation of the birth process as an example of the expanded information potentials of segmental imaging procedures].

A method is presented that enables the use of (static) informations from magnetic resonance imaging (MRI) for (dynamic) biomechanical analysis. Using a specially developed software MRI pixel matrices are colour-coded and--according to the principle of same density--line data are created. After sectional attribution of the resulting polygons a three-dimensional mesh of so-called finite elements is created which can then be used in deformation analysis. This method is exemplified by a project dealing with the simulation of birth mechanics, which is finally aimed at validating the results from radiologic pelvimetry. First analyses show that even under foetal head moulding conditions, being considered as normal, such sensitive structures as the cerebellum, brain stem as well as the ventricles with the plexus chorioidei are to be found within the maximum isobars within a range of 104-140 N(10.6-14.3 kp).

Adult↗
PubMed1992

[Digital image intensifier radiography--what dose for what clinical problem?].

Due to a wide dynamic range it is possible to vary the dose of DIIR for each type of examination according to the required image quality. To define the possible decrease of dose compared to film-screen radiography (speed 200) the dependence of spatial resolution and contrast detectability upon dose was evaluated. We used a Polytron 1000 which was connected to a Siregraph D and an Optilux 57 (Siemens). Acquisition parameters were fixed for different types of examination and tested by imaging anthropomorphic phantoms as well as patients (n = 114). Our results demonstrate that the dose can be reduced by 60% for double-contrast examinations and by 85% for mono-contrast studies. Although DIIR is less suited for chest and skeletal imaging, a 14 cm image intensifier can be used for imaging small lesions. If poor image quality is acceptable (e. g. pelvimetry, sometimes in paediatrics), a maximum reduction of 95% is possible.

Humans↗
PubMed1991

[The value of digital imaging techniques in skeletal imaging].

The clinical value and the imaging characteristics of digital radiography systems (image intensifier (I.I.) radiography: Polytron/Siemens, storage phosphor radiography: PCR/Philipps) in skeletal imaging were compared with film-screen radiography and 100 mm technique. The influence of spatial and contrast resolution, entrance dose and detectability of lytic, osteoblastic and cortical lesions were studied as well as the images of 25 parallel examined patients. Only with the small image intensifier (diameter 14 cm) the quality of 100 mm technique and digital I.I. radiography was equivalent to storage phosphor and film-screen radiography. Storage phosphor radiography seems to be better qualified than I.I. radiography to replace conventional techniques in skeletal imaging.

Bone Neoplasms↗
PubMed1989

[Digital image intensifier radiography--one year's experience with a Polytron system].

Since January 1988, digital image intensifier radiography has been used in the Clinic in Mannheim for DSA examinations and also in place of conventional screen/film examinations. Measurements have shown that compared with 100 mm and film/screen formats, digital radiography has poorer spatial resolution, but improved contrast resolution. The most common use of digital radiography was for examinations of the gastrointestinal tract. Using the demonstration of the mucosal fine relief pattern as a criterion of image quality, digital image intensifier radiography was able to achieve this satisfactorily. Comparison with film/screen examinations showed no loss of diagnostic information. Advantages of image intensifier radiography are reduced radiation dose, the possibility of postprocessing and economy. On the basis of 399 examinations, digital image intensifier radiography is now firmly established as part of the daily routine of the Mannheim Clinic.

Evaluation Studies as Topic↗
PubMed1989

[Obstetric pelvimetry using digital image intensifier radiography].

Obstetric pelvimetry can be performed by digital image intensifier radiography using very low exposure doses. Comparative measurements show a reduction of the entrance dose to 5% of conventional respectively 15% of high speed film-screen radiography. Phantom measurements have shown an accuracy of +/- 5 mm. In 30 patients the transverse diameter of the pelvic entrance, of the interspinous and of the intertuberous level as well as the sagittal diameter of the pelvic entrance and outlet were measured. Pelvimetry is indicated for the early recognition of certain risks if anamnestic (previous Caesarean section), clinical (eg. external pelvimetry) or fetometric features indicate the evidence of disproportion. As a radiological method the image intensifier radiography appears particularly recommendable in respect of its low exposure dose and the possibility of interactive measurements with subsequent documentation of the diameters and values.

Female↗
PubMed1989

[Hysterosalpingography with digital image intensification radiography].

Digital image intensifier radiography (Siemens/Polytron) offers the chance to reduce patient exposure dose in hysterosalpingography (HSG) by 85% compared with conventional film/screen radiography and by 11% compared with the 100 mm technique. By appropriate choice of the parameters the signal-to-noise ratio was adapted to the detectability of the diagnostic information (variation of the dose). Thirty patients were examined with the 28 cm image intensifier and an image intensifier input dose of 50 microR. The diagnostic image quality was assessed being aware of the results of laparoscopy or surgery; in 29 cases the quality was classified very good without any limitations. Digital image intensifier radiography offers additional advantages over conventional x-ray units: the images are directly available on the monitor and offer the possibility of post-processing.

Adult↗
PubMed1988

[Documentation of digital image information--video or laser imager?].

The quality of hardcopies produced by a video- or laser imager was compared. Laser printing could be performed after analogue or digital data transmission, whereas the video imager allowed only analogue data transfer. Evaluation of CT-, MR-, DSA- and radiographic images showed no difference in diagnostic information between video and laser-produced hardcopies. For large formats (35 X 35 cm.), laser images produced by digital transmission were considerably superior to video signals and analogue transmission. There were advantages and disadvantages of both types of imaging, depending on the size of the matrix, the type of image produced, ease of use and capital cost.

Copying Processes↗
PubMedDate not supplied

[Does the "fatty pelvis" exist? Quantitative computer tomography studies].

50 Patients weighing between 45 and 114 kg underwent standardized computed tomography of the pelvis. Fat compartments from inside and outside of the small pelvis were assessed quantitatively by means of tracing the fat tissue borders and planimetry. Fat compartments within the small pelvis showed a rather weak correlation with body weight and the so called Rohrer-Index as a weight/height-Index, correlations with the latter being slightly better. From the fat compartments within the single levels the functional reduction of birth channel diameters caused by fat tissue was calculated for. The weight/height-index dependent increase of space demand within the birth channel was rather pronounced at the pelvic brim becoming slighter when reaching mid-pelvis or even pelvic outlet. Hence, the common assumption can no longer be maintained, that adiposity necessarily causes soft tissue dystokia due to larger fat compartments within the small pelvis.

Adipose Tissue↗
PubMedDate not supplied

[Changes in pelvic anatomy in 8 decades--computerized tomography study of obstetrically relevant pelvic measurements].

An increasing proportion of obstetric operative procedures due to cephalopelvic disproportion gave raise to the question, whether there has been a change in pelvic anatomy during the past decades. In a retrospective evaluation of 467 computerized pelvic tomograms of patients aged between 18 and 88 years relevant parameters of pelvic proportion were determined. As these parameters are not subject to age-conditioned changes, the values may be viewed as representative for the time of patients' birth or fertility period respectively. Changes in pelvic anatomy turned out to be complex: The transverse elliptic shape of pelvic inlet changed into sagittal elliptic form, the pelvic midplane is contracted progressively, sacral concavity is reduced. Obviously, this obstetrically adverse development is influenced by the fact, that unfavourable pelvic conformation can be transmitted more intensively by the generous indication for cesarean section. This development is contrasted by the circumstance of fetal acceleration. Therefore, an increase in cephalopelvic disproportion has to be expected. For the sake of a safe obstetrical management in these situations the generous use of ante partum pelvimetric diagnosis seems to be advisable.

Adolescent↗
PubMedDate not supplied

[New aspects of radiologic pelvimetry. Digital image intensification radiography: preliminary results of validation possibilities and results in various types of pelvic disproportion].

Within 1 year with 1325 births 54 cases necessitated operative obstetric intervention due to a disproportion between fetal head and maternal pelvis. In 40 cases radiologic pelvimetry was performed, using the conventional technique. 75% of cases turned out to be due to a midplane or outlet contraction. As, on the one hand, this type of pelvic disproportion seems to be of increasing importance, on the other hand generously adoperated radiologic diagnosis is not well accepted by the patients due to X-ray burden, Digital Image Intensifier Radiography (DIR) has been introduced for pelvimetry. X-ray burden amounts to only 5% of that of the conventional technique. Enhanced postprocessing and interactive measurement possibilities are further advantages of DIR. Using the appropriate softwear, interactive measurement results are characterized by the lack of mistakes due to X-ray divergence, if only the distance between measurement level and desk surface is known. By analyzing 30 computer tomograms measurement levels of the most important pelvic distances could be calculated in relation to the position of the anterior iliac spine. These relations show a very low interindividual variation. Thus, possible errors in measurement amount to a maximum of only 3.5%. The evaluation of our cases reveals the necessity to reassess the normal ranges for pelvic parameters, for the use of those deriving from conventional pelvimetry failed to describe correctly the anatomy of birth channel. For this sake, additional measurements, esp. of sacral and pelvic outlet anatomy have to be performed. Based upon these measurements, a computer aided modelling of the birth channel and a simulation of the birth could be achieved.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer Simulation↗