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K P Hermann

Publications and source records attributed to K P Hermann.

33 records · Page 2Linked to original sources
PubMed1997

[Digital storage phosphor mammography in a magnification technic: experimental studies for spatial resolution and for detection of microcalcifications].

PURPOSE: Since the routine use of storage phosphor systems for mammography has been limited by its inadequate spatial resolution of 5 linepairs/mm, a combination of a magnification mammography technique with storage phosphor plates was investigated to detect microcalcifications. MATERIAL AND METHODS: A new mammography system with a microfocus tube using an anode of 0.05-0.12 mm allowed to obtain survey views of the breast with 1.7x magnification (m), and spot views with 4x magnification. The digital image receptor comprised a high resolution storage phosphor plate. To determine spatial resolution, contrast transfer curves were obtained, and the detection of microcalcifications was investigated by ROC (receiver operating characteristic) analysis. RESULTS: Spatial resolution for digital survey views (m = 1.7) was 8 linepairs/mm and for spot views (m = 4) was 18 linepairs/mm. ROC analysis demonstrated a significantly higher performance of the digital magnification technique compared to the conventional screen-film mammography technique. CONCLUSIONS: The limitations of digital mammography with respect to spatial resolution can be overcome by using a high magnification technique.

Breast Diseases↗
PubMed1997

[DIMA-magnification mammography. Phantom studies on image quality and radiation exposure of the patient].

PURPOSE: A mammographic system has been developed to provide direct radiographic magnification; investigation of image quality and radiation exposure for surveys and aimed exposures were carried out on phantoms and the results compared with two modern screen methods. MATERIAL AND METHOD: Image quality was defined by contrast transfer function, resolution of low contrast, contrast of large areas and recognition of low contrast detail, using suitable phantoms. Measurements of entrance surface dose were made with a 1 cm3 flat chamber. RESULTS: For survey examinations, the new mammographic system provided image quality equal to a screen system but using 50% radiation dose. For localised views, the new system used similar radiation dose but provided significantly better demonstration of diagnostic detail. CONCLUSION: Using a focal spot of 40-120 microns, the new mammographic system provides markedly improved direct radiographic magnification. With reduced radiation exposure at times, there is a significant gain in diagnostic information compared with current standard systems.

Female↗
PubMed1997

[Digital image magnification mammography with the storage-screen technique. Standardized and findings-oriented image processing parameters].

Present day mammography has not been able to make use of the advantages of digital luminescence radiography because of the limited spatial resolution. The recent development of electromagnetic focusing x-ray tube with effective focal spot sizes from 0.04 to 0.12 mm allows radiographic direct magnification with less geometric blur. It is now possible to combine direct magnification mammography with digital luminescence radiography. By combining high quality storage phosphor screens with an HQ-workstation a spatial resolution of 8 lp/mm is possible for 1.7-fold magnification. For 4-fold spot magnification views spatial resolution can be theoretically increased to approx. 20 lp/mm. One important advantage of digital radiography is the possibility of image-post-processing. This article presents two sets of standard parameters and three sets of image dependent parameters for better imaging of specific lesions, such as microcalcifications. The introduction of the the storage phosphor screen technique in mammography is one step in the development of direct digital radiography. Further interesting perspectives for the future include post-processing programs for detecting suspicious lesions which are already being clinical tested.

Breast Neoplasms↗
PubMed1996

Must radiation dose for CT of the maxilla and mandible be higher than that for conventional panoramic radiography?

We evaluated the feasibility of performing preoperative spiral CT of the maxilla and mandible with a radiation dose similar to that used for conventional panoramic radiography. The skin entrance doses of radiation used for spiral CT (collimation, 1 mm; pitch, 2; tube voltage, 80 kV; tube current, 40 mA) and for panoramic radiography (75 kV, 8 mA, 15 seconds) were measured in one patient by using thermoluminescent dosimeter chips. Results were 0.56 +/- 0.06 mGy for CT and 0.59 +/- 0.04 mGy for radiography. Image quality was adequate for preoperative implant planning. Spiral CT of the mandible and maxilla may therefore be feasible with a radiation dose of similar magnitude as that used for conventional panoramic radiography.

Dental Implants↗
PubMed1995

[An anatomically adapted variation of the tube current in CT. Studies on radiation dosage reduction and image quality].

PURPOSE: To assess the impact of a method for anatomically adapted tube current variation. The resulting CT image quality was evaluated quantitatively and qualitatively. METHODS: CT scans of 100 patients were performed with a constant tube current (Group 1) and another 100 patients with an anatomically adapted tube current (Group 2). The CT tube current was varied during a 360 degrees tube rotation reflecting the measured density values extracted from two perpendicular scout views. The standard deviation of densities of defined regions was measured. The image quality was ranked (1 = non-diagnostic-5 = excellent) by three radiologists. RESULTS: The effective tube current could be reduced by an average of 8.9% (0-20.4%). The mean tube current reduction depended on the body region: pelvis (13.2%), abdomen (8.4%) and thorax (3.3%). The image quality was not significantly reduced in Group 2. CONCLUSION: The method for anatomically adapted tube current variation leads especially in the pelvis to a significant mAs reduction without considerable loss of image quality.

Aged↗
PubMed1995

[A bimetal anode with tungsten or rhodium? Comparative studies on image quality and dosage requirement in mammography].

PURPOSE: The impact of different anode materials (tungsten and rhodium) on spatial resolution, image contrast and radiation exposure was studied. MATERIALS AND METHODS: Two mammographic systems providing bimetal x-ray tubes (Mo/W and Mo/Rh) were compared by imaging a breast radiography phantom with additional acrylic plates from 3 to 8 cm thickness. Spatial resolution was evaluated using a line bar pattern. Image contrast was assessed by measuring the ratio of optical densities in a acrylic step-wedge. The entrance dose was measured with a low energy ionisation chamber. RESULTS: The spatial resolution was about 13 lp/mm regardless of the beam quality. The image contrast depended substantially on the thickness. A similar image contrast was found with Mo/Mo, Mo/Rh and Rh/Rh for simulated breast thicknesses of 4 to 6 cm and with Rh/Rh and W/Rh for 7 cm. In comparison to Mo/Mo the dose reduction was significant for Mo/Rh (35%), Rh/Rh (50%) and W/Rh (60%). CONCLUSIONS: Bimetal x-ray tubes provide optimal conditions for screen film mammography of both normal and dense breasts, allowing good contrast and dose reduction by using the adequate anode/filter-combination.

Electrodes↗
PubMed1995

An anthropomorphic phantom for periodontal radiography.

OBJECTIVE: To construct an anthropomorphic phantom for periodontal radiography. METHODS: The phantom material for the spongiosa was produced by melting polyethylene with calcium hydroxyapatite. Compact bone and teeth were simulated by mixing silicone rubber with calcium hydroxyapatite and calcium carbonate respectively. RESULTS: Radiographs of the phantom show nearly all the structures relevant for periodontal radiography. Measurements of X-ray attenuation and optical density correspond to those of the human mandible. Any defect in the periodontal bone can be reproduced. CONCLUSION: The new phantom will be useful for research and education.

Alveolar Bone Loss↗
PubMed1993

Solid phantom material for the dosimetry of iodine-125 seed ophthalmic plaques.

PURPOSE: A tissue-equivalent solid phantom material, RE-1, closely simulating the radiological attenuation and scattering properties of the human eye for the iodine-125 photon spectrum and their Compton-scattered secondary photons, was fabricated on a polyethylene base with CaCO3 and MgO as inorganic additives. METHODS AND MATERIALS: A 24 mm diameter spherical phantom was made from 1.1 mm thick sheets of RE-1, and holes were drilled in which 1 mm3 TLD cubes were placed. RESULTS: The radial dose function g(r), which determines the dose profile on the transverse axis, was measured in a quasi-infinite phantom of RE-1. CONCLUSION: The values obtained deviate only slightly from those for a quasi-infinite phantom made from water-equivalent material.

Brachytherapy↗
PubMed1993

Autoradiography for iodine-125 seeds.

To study the interior design of model 6702 and 6711 iodine-125 seeds contact autoradiographs were performed using mammography film. Improved resolution was obtained using a pin-hole camera with a hole of 0.1 mm x 0.1 mm. With these techniques, qualitative determination of the relative activity distribution within each seed was possible. The number of the activated resin spheres and the positions of the centers of these spheres can be exactly determined. A model calculation shows, that variations in the arrangement of the activated spheres within a seed have a moderate influence on the dose distribution at source distances below 10 mm. Knowing the exact source configuration may be useful when comparing dose calculations with measured data for model 6702 125I seeds which are currently employed in ophthalmic plaque and implant therapy of other tumors.

Autoradiography↗
PubMed1991

Dosimetry and physical treatment planning for iodine eye plaque therapy.

The dosimetry of eye plaques loaded with iodine-125 seeds (type 6702) was performed by means of computer calculations and measurements with thermoluminescent dosimeters (TLD). Measurements of the depth dose distribution (2-25.5 mm) along the transverse axis of a single seed were performed in water equivalent phantom material. The transverse axis attenuation and geometry factor F(r) was obtained by applying a least squares fit to the measured data. Based on the resulting radial dose function, a computer program was developed which calculates dose distributions within the eye for arbitrary loading and placement of the eye plaque. The computational results were verified by TLD measurements in an eye phantom.

Brachytherapy↗
PubMed1990

[Development and dosimetry of a 125 iodine applicator for brachytherapy of intraocular tumors].

Due to the low gamma energy (27-35 ke V), iodine 125 is especially suitable for brachytherapy of intraocular tumors. 125I is available as encapsulated seeds. Applicators can be individually loaded with these seeds to accommodate the shape of the tumor as much as possible. To measure the depth-dose distribution LiF thermoluminence detectors (TLDs, 1 mm3) are embedded in an RW-1 eye phantom at various distances and directions from the high active plaque positioned at the top of the phantom. To obtain the three-dimensional dose distribution, the TLDs are read after exposure for the appropriate time period. Based on experimental measurements of the 125I plaque, a computer program is developed to calculate the dose distribution within the eye and the radiation time for intraocular tumors. These results are very similar to those obtained when using mathematical equations published in the literature. In summary, three-dimensional dose distribution at various distances from an 125I eye plaque has been experimentally determined using a new method. This is an important prerequisite for introducing 125I plaques into the treatment of intraocular tumors.

Brachytherapy↗
PubMed1989

[Dosimetry of ruthenium applicators with an eye phantom and small volume thermoluminescence detectors].

Even though 106Ru/106Rh applicators have been in clinical use over more than two decades for the radiotherapy of malignant uveal melanomas, the dosimetry of emitted beta radiation is still a physical problem. The dose rate at the applicator surface and the depth dose in tissue equivalent material can be determined only within +/- 30% error. Using new cubic-shaped thermoluminescence detectors (TLD) with small volume the dose distribution is examined in water equivalent material (RW-1). The spatial resolution is 14 times better compared to the previous technique. From dose measurements in an eye phantom the homogeneity of nuclide deposition and the depth dose distribution of a 106Ru/106Rh applicator are determined.

Brachytherapy↗
PubMed1987

[Measures for reducing exposure to scattered radiation in urologic roentgen diagnosis].

A simple device to reduce the urologic examiner's exposure to radiation is presented. The doses the examiner and his assistant staff are exposed to performing various methods of urologic radiodiagnosis were measured and the following exposure to radiation determined with and without radioprotective device. The measurements demonstrate, that already by simple measures considerable reduction of the exposure to radiation can be obtained for examiner and assistant personnel. The frequently neglected importance of scattered radiation resulting from urologic radiography is discussed.

Humans↗
PubMed1985

Polyethylene-based water-equivalent phantom material for x-ray dosimetry at tube voltages from 10 to 100 kV.

A water-equivalent plastic material RW-1, in the form of thin foils as well as of thicker sheets, has been produced by melting powdered polyethylene together with CaCO3 and MgO. The mixture has been developed in a three-step procedure, starting with provisional mixtures and using data from their measured attenuation curves to determine the final composition. The attenuation curves of RW-1 and of water, as well as their backscatter factors, are in excellent agreement for x-ray tube voltages from 10 to 100 kV.

Humans↗