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M Scholz

Publications and source records attributed to M Scholz.

At least 19 recordsLinked to original sources
PubMed2006

[Radiation exposure in full-field digital mammography with a selenium flat-panel detector].

PURPOSE: Calculation of the average glandular dose for mammography on a full-field digital mammography system using a selenium flat-panel detector. MATERIALS AND METHODS: Mammographic examinations were carried out using the Selenia digital mammographic system from Lorad/Hologic. 1992 mammographies of 500 patients in cranio-caudal and medio-lateral projections were evaluated. Based on the recorded exposure conditions (tube voltage, tube loading, filtration, compressed breast thickness), the entrance surface air kerma was calculated by multiplying the tube loading by the measured tube output and was corrected according to the inverse square law. The average glandular dose was determined for each exposure by multiplying the entrance surface air kerma value by the relevant conversion factor for a breast composition of 50 % adipose tissue and 50 % glandular tissue by weight. RESULTS: The mean values for patient age and compressed breast thickness were 61 years and 58 mm, respectively. The average glandular dose was 1.57 mGy for a single view (1.46 mGy for cranio-caudal view images and 1.68 mGy for medio-lateral view images). CONCLUSION: Full-field digital mammography with a selenium flat-panel detector requires a dose similar to that of units with a flat-panel detector based on amorphous silicon and a dose approximately 20 % lower than that of conventional screen/film mammography.

Body Burden↗
PubMed2006

Deutsch-jozsa algorithm using triggered single photons from a single quantum dot.

We demonstrate a two-qubit Deutsch-Jozsa algorithm with single photons from a single InP quantum dot. The qubits are implemented via the spatial mode and the polarization of a single photon. Our photon source is operated both under continuous and pulsed excitation, the latter allowing deterministic quantum logic by generating photons on demand with a strong suppression of two-photon events. The computation reached a success probability of up to 79%. We also exploit the concept of decoherence-free subspaces that helps to make our experimental setup robust against sources of phase noise.

Journal Article↗
PubMed2006

Rapid calculation of biological effects in ion radiotherapy.

We describe a method for fast calculation of biological effects after ion irradiation. It is an alternative derivative of the established local effect model (LEM) and has been integrated into GSI's TRiP98 treatment planning system. We show that deviations from our classic approach for treatment planning are less than 5% for therapeutical doses, but calculational speed can be improved by one to two orders of magnitude. This will allow sophisticated methods of treatment planning for ion irradiation, taking biological effects fully into account.

Body Burden↗
PubMed2006

Neurosurgical operations with the patient in sitting position: analysis of risk factors using transcranial Doppler sonography.

BACKGROUND: One major risk factor of the sitting position for neurosurgery is air embolism, especially in patients with persistent foramen ovale (PFO). The first aim of this prospective study was to evaluate a bedside method for detecting PFO using transcranial Doppler sonography (TCD) with contrast medium. A second aim was to address intraoperative monitoring, patient positioning and the occurrence and clinical relevance of air embolism. METHODS: Ninety patients with a mean age of 56.5 yr (range 14-81 yr) undergoing surgery in sitting position were investigated by TCD with contrast agent to detect functional PFO, that is PFO that can be provoked with a Valsalva manoeuvre. In patients in whom TCD was not possible, transcranial duplex sonography, duplex sonography of the carotid artery at the neck or transoesophageal ECG was performed. RESULTS: In 26 patients PFO was detected. Thirteen of them presented a persistent PFO with high-intensity transient signal in both middle cerebral arteries without Valsalva manoeuvre. The intraoperative positioning in these patients was adapted to the risk for a paradoxical air embolism, although, after surgical recommendations, three patients with a persistent PFO underwent surgery in sitting position. Intraoperative air embolisms were seen in 8 of 80 patients in sitting or semi-sitting position with air aspirable through the central venous catheter. CONCLUSION: To address the risk of a paradoxical air embolism, especially in patients undergoing surgery in sitting position, preoperative detection of PFO is advisable. If surgery is performed in seated PFO patients, additional monitoring and special care are warranted.

Adolescent↗
PubMed2006

[Influence of ML-1 standardized mistletoe extract on the quality of life in head and neck cancer patients].

BACKGROUND: ML-1 standardized mistletoe extracts have been recommended for increasing the health-related quality of life in cancer patients. PATIENTS AND METHODS: The EORTC questionnaire QLQ-C30((V2)) was given to a randomly chosen subgroup of 399 patients of a prospective, randomized, open, multi-center trial. A total of 200 patients from this trial were randomized for ML-1 treatment (1 ng/kg body weight ML-1 was injected subcutaneously twice weekly over a 60-week period. Treatment cycles of 12 weeks were followed by a break of 4 weeks (between weeks 12-16, 28-32, and 44-48)). The remaining 199 patients formed the control group. RESULTS: Patients completed questionnaires before the start of their treatments at week 0 and continued until week 156. The compliance rate was high: 3611 questionnaires were available, which equals a median of nine longitudinal measurements per patient between weeks 0 and 156. Analysis did not indicate any improvement in the quality of life for either group. A significant decrease in quality of life, however, was seen in patients undergoing radiotherapy. In these patients, the global state of health was reduced and four symptom scales were significantly worse. CONCLUSION: Our results demonstrated no improvement in the quality of life in head and neck cancer patients when treated with ML-1 extract.

Adult↗
PubMed2006

Intra- and extravascular volume status in patients undergoing mitral valve replacement: crystalloid vs. colloid priming of cardiopulmonary bypass.

BACKGROUND AND OBJECTIVE: Cardiopulmonary bypass is associated with changes of intra- and extravascular volume status often resulting in cardiopulmonary dysfunction. The purpose of this prospective double-blind study was to evaluate the influence of different priming solutions of the extracorporeal circuit on intra- and extravascular volume status and haemodynamics in patients undergoing elective mitral valve replacement. METHODS: Twenty-two patients with mitral valve insufficiency were randomly allocated into two equal groups. In Group 1 cardiopulmonary bypass was primed with a nearly isooncotic solution consisting of 4% albumin. The second group received a pure crystalloid priming solution. The thermo-dye indicator dilution technique was used for the assessment of cardiac output, central and pulmonary blood volume, right ventricular end-diastolic volume and total blood volume. RESULTS: Patients in the crystalloid group showed increased intraoperative fluid requirements. Significantly more fluid was accumulated in the extravascular space whereas total blood volume was decreased after surgery. Stroke volume index (SVI) was significantly decreased in the immediate postoperative period when compared to baseline. As indicated by the increase in extravascular fluid content after surgery, both colloid and crystalloid priming volumes were transferred to the extravascular space. CONCLUSION: The use of colloid priming solutions in patients with mitral valve insufficiency leads to less fluid requirements and significantly reduced fluid shift in the interstitium. However, these changes are not associated with changes in haemodynamic parameters or short term outcome.

Adrenergic beta-Agonists↗
PubMed2006

Analysis of surgical management of calvarial tumours and first results of a newly designed robotic trepanation system.

This study was performed to evaluate the surgical strategy in patients with calvarial tumours, in order to design and modify a robot-assisted trepanation system. A total of 75 patients underwent craniectomy for the treatment of calvarial tumours during the 10-year period from 1993 to 2002. The patients' complaints, the size, location and histology of the tumour, and the various cranioplasty techniques used were analysed retrospectively. In a second procedure several craniectomies at typical locations according to the study's results were performed in a laboratory setting using a hexapod robotic tool, constructed at the Helmholtz-Institute, RWTH Aachen University, and plastic model heads. The workflow was documented and the reproducibility and the accuracy of the procedure were registered. A total of 83 surgical procedures were performed on 75 patients. The majority (87 %) of lesions treated surgically were located in the frontal, temporal and anterior parts of the parietal region. Histological examination revealed benign lesions in 66 % of the patients and dural involvement in 46 %. According to these results craniectomies were performed using the robotic system. Mean positioning accuracy of the robotic system while milling was 0.24 mm, with a standard deviation of 0.04 mm, and maximum error under 1 mm. Craniectomies leaving a 1-mm layer of the tabula interna intact to ensure a healthy dura were performed in several regions successfully. The majority of calvarial tumours, requiring surgical treatment in our patients, were located in cosmetically relevant areas in which drilling can be carried out with the robotic trepanation system. Consequently, the surgical approach had to be planned carefully in order to achieve a good cosmetic outcome.

Adolescent↗
PubMed2006

Dynamic cerebral autoregulation in patients with ruptured and unruptured aneurysms after induction of general anesthesia.

INTRODUCTION: Blood pressure management in patients undergoing surgery for clipping of aneurysms is demanding. More information about the ability of cerebral vessels to normally regulate cerebral blood flow may have a direct influence on the intraoperative management. In patients with subarachnoid hemorrhage (SAH) a disturbance of cerebral autoregulation has been reported and it correlated with the severity of the bleeding in these studies. The impairment of autoregulation was demonstrated using static measurements of cerebral pressure autoregulation. However, the dynamic component of the autoregulatory capacity seems to be of importance in the acute setting after SAH. The aim of this study was to evaluate dynamic pressure autoregulation in patients undergoing surgery for intracranial aneurysms. PATIENTS/MATERIAL AND METHODS: 36 patients with a mean age of 45 years were evaluated, 26 patients with acute SAH, 10 patients with unruptured aneurysms. Cerebral autoregulation in normocapnia was tested using thigh cuffs to alter arterial blood pressure and continuous registration of the blood flow velocities with transcranial Doppler sonography. After the induction of general anesthesia under normocapnia the autoregulatory index (ARI) was calculated (values between 0-9). Patient groups were compared using Wilcoxon- and Spearman's rank test. RESULTS: The two patient groups were comparable with regard to gender, age, PaCO(2), blood flow velocities and blood pressure. In patients with SAH mean ARI was 3.1/3.3 (right/left side) compared to 4.7/4.6 (right/left side) in patients without SAH. The difference was statistically significant (Wilcoxon p = 0.0399). The degree of impairment of the autoregulatory capacity increased significantly (p = 0.006) with the severity of the SAH (Hunt&Hess and Fisher scale). CONCLUSION: Dynamic pressure autoregulation is impaired in patients after SAH compared to patients without SAH and correlates with the severity of the SAH. We propose that autoregulation should be measured in all patients with SAH or that an impaired autoregulation should be taken into account in patients with SAH undergoing surgery in the acute phase.

Adult↗
PubMed2005

Quantile estimation to derive optimized test thresholds for random field statistics.

We present a numerical method to estimate the true threshold values in random fields needed to determine the significance of apparent signals observed in noisy images. To accomplish this, a quantile estimation algorithm is applied to derive the threshold with a predefined confidence interval from a large number of simulated random fields. Also, a computationally efficient method for generating a random field simulation is presented using resampling techniques. Applying these techniques, thresholds have been determined for a large variety of parameter settings (smoothness, voxel size, brain shape, type of statistics). By means of interpolation techniques, thresholds for additional arbitrary settings can be quickly derived without the need to run individual simulations. Compared to the parametric approach of Worsley et al. (1996) (Worsley, K.J., Marrett, S., Neelin P., Vandal, A.C., Friston, K.J., Evans, A.C., 1996. A unified statistical approach for determining significant signals in images of cerebral activation. Hum. Brain Mapp. 4, 58-73) and Friston et al. (1991) (Friston, K.J., Frith, C.D., Liddle, P.F., Frackowiak, R.S. 1991. Comparing functional (PET) images: the assessment of significant change. J. Cereb. Blood Flow Metab. 11(4), 690-699), and to the Bonferroni approach, these optimized thresholds lead to higher levels of significance (i.e., lower p values) with a specific amount of activation especially with fields of moderate smoothness (i.e., with a relative full width half maximum between 2 and 6). Alternatively, the threshold for a specified level of significance can be lowered. This improved statistical sensitivity is illustrated by the analysis of an actual event related functional magnetic resonance data set, and its limitations are tested by determining the false positive rate with experimental MR noise data. The grid of estimated threshold values as well as the interpolation algorithm to derive thresholds for arbitrary parameter settings are made available over the internet (http://neuro2.med.uni-magdeburg.de/quantile_estimation).

Algorithms↗
PubMed2005

3-Dimensional computed tomographic angiography for use of surgery planning in patients with intracranial aneurysms.

BACKGROUND: After subarachnoid haemorrhage (SAH) diagnostic evaluation of the underlying cause is warranted since the rebleeding rate is high. The objective of the study was to answer the question, whether 3-Dimensional computed tomographic angiography (3D-CTA) is able to accurately determine the surgical indications in patients with intracranial aneurysms. METHODS: After performing 3D-CTA the size of the aneurysm, direction of the aneurysmal dome, neck position and variants of the circle of Willis were analysed. Surgery was performed solely on CTA data in those cases, where the aneurysm was clearly visible. If the findings were negative or inconclusive, intra-arterial digital subtraction angiography (DSA) was also done. FINDINGS: Between January 2001 and December 2002 100 patients (68 F, 32 M) were examined and 123 aneurysms (86 ruptured and 37 unruptured) were diagnosed. All patients received CTA preoperatively and in 27 patients selective DSA was additionally performed. Postoperatively in 34 patients the operative result was checked by DSA. A good correlation between CTA and the intra-operative findings was present in 92 of 100 patients. One aneurysm was not seen on CTA, but was on DSA. In four cases we could confirm DSA findings in CTA after re-evaluation of the data. In three cases neither CTA nor DSA clearly showed an aneurysm, but it was confirmed during surgery. A good correlation between CTA and DSA was found in 60 of 61 patients (98%). The correlation between CTA and intra-operative findings was good as expected in 92 patients, in 5 patients an aneurysm was detected on re-evaluation. Only one aneurysm could not be demonstrated by CTA but in DSA. CONCLUSION: CTA is less invasive, less time consuming, cheaper and easier to demonstrate the essential information regarding the aneurysm than DSA. We therefore recommend that following a careful analysis most aneurysms - 92% - can be operated solely on CTA data.

Adult↗
PubMed2005

Hereditary non-polyposis colorectal cancer: clinical and molecular evidence for a new entity of hereditary colorectal cancer.

BACKGROUND: Hereditary non-polyposis colorectal cancer (HNPCC) is clinically defined by familial clustering of colorectal cancer and other associated tumours. METHODS: By thorough molecular and clinical evaluation of 41 families, two different groups were characterised: group 1, 25 families with truncating mutations in MLH1 or MSH2 (12 novel mutations); and group 2, 16 Amsterdam positive families without mutations in these genes and without microsatellite instability in their corresponding tumours. RESULTS: Significant clinical differences between these two groups were found. Firstly, earlier age of onset for all colorectal cancers (median 41 v 55 years; p < 0.001) and all tumours (median 43 v 56 years; p = 0.022) was observed, comparing groups 1 and 2. Secondly, 68% of the index colorectal cancers were localised proximally of the splenic flexure in group 1 compared with 14% in group 2 (p < 0.010). Thirdly, more synchronous and metachronous colorectal (p = 0.017) and extracolorectal tumours (p < 0.001) were found in group 1. Fourthly, a higher colorectal adenoma/carcinoma ratio (p = 0.030) and a tendency towards more synchronous or metachronous adenomas in group 2 (p = 0.084) was observed, indicating a slower progression of adenomas to carcinomas. As three mutation negative tumours revealed chromosomal instability after comparative genomic hybridisation, these tumours may be caused by one or more highly penetrant disease alleles from the chromosomal instability pathway. CONCLUSION: These data show that HNPCC includes at least two entities with clinical and molecular differences. This will have implications for surveillance programmes and for cancer research.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Application of a newly developed visual navigation system in humans. First results.

A visual navigation system (VN) was developed which uses intraoperatively stored endoscopic images together with their specific 3D-address. A special calibration enables one to recalculate the distortion of the endoscopic images. Several modules (e. g., landmark tracking, virtual back-movement) are offered to the neurosurgeon. The system was tested in 12 human subjects during neuroendoscopic interventions and worked without problems in nearly all cases. The possibilities of digital image navigation can be used especially for control of instrument movement in case of red-out situations or blurred vision. Many further developments of the VN system are possible in order to increase the safety of neuroendoscopic interventions.

Adolescent↗
PubMed2005

Accidental dural tears occurring during supratentorial craniotomy -- a prospective analysis of predisposing factors in 100 patients.

OBJECT: Accidental dural tears during craniotomy constitute a possible source of CSF leakage and wound infection. This can turn an elective procedure into a complicated and cost-intensive problem. Only a few studies have addressed the incidence of dural tears, but there have been many studies dealing with various techniques that can be employed to repair dural tears. The present study was carried out to analyze predisposing factors for dural tears during trepanation in order to optimize the design of a robot-assisted trepanation system. PATIENTS: 100 patients were analyzed prospectively. An evaluation sheet was designed to document size and location of the lesion and the craniotomy, the geometry and number of burr holes, and the auxiliary tools used during bone flap removal. Furthermore, the suspected histology was noted and anatomical facts, including cranial vault thickness and the presence of hyperostosis frontalis interna, were documented. RESULTS: In 100 craniotomies performed, in the majority of cases (64 %), in order to gain access to intracerebral lesions, 30 dural tears were seen, involving both dural layers in 26 cases. There were 26 tears located under the margins of the craniotomy; the length was 0-3 cm in 18 patients (69 %). Significant predisposing factors were the thickness of the cranial vault and the presence of a hyperostosis frontalis. Furthermore, the location (frontal) and the diagnosis of an extracerebral pathology, including meningiomas, were significant factors for dural tears. Elderly patients and the use of the drill to complete the trepanation were also significant predisposing factors. Dural repair was done using suturing, in most of the cases combined with a free periostal flap. Central dural tears were integrated into the planned dural opening. A vascularized flap or muscle was used in the minority of cases. Postoperative cerebral fluid leakage was seen in two patients, wound infections in three. CONCLUSIONS: Dural tears occurring during craniotomy cannot be prevented, when predisposing factors are taken into account. The absence of brain damage may due to two factors: 1) in elderly patients with hyperostosis, an additional atrophy of the brain is present; 2) extracerebral tumors, with their space-occupying growth, shift the underlying brain away from the calvaria. Considering the design of a robot-assisted trepanation system, the following conclusions seem possible: dural tears cannot be avoided because predisposing factors are overriding. For improved safety, additional, specialized instrumentation is required.

Adolescent↗
PubMed2005

[Vertebroplasty and kyphoplasty in osteoporotic fractures of vertebral bodies -- a prospective 1-year follow-up analysis].

PURPOSE: Kyphoplasty and vertebroplasty offer two minimally invasive operative stabilization procedures for vertebral compression fractures. The purpose of this prospective study was to investigate whether both procedures are able to reduce pain and to preserve postoperative vertebral height during a 1-year follow up. MATERIALS AND METHODS: Osteoporotic vertebral fractures were treated in 42 cases, 20 patients (15 female, 5 male) underwent vertebroplasty, 22 patients (14 female, 8 male) underwent kyphoplasty. 32 vertebral fractures were treated with vertebroplasty and 35 vertebral fractures were treated with kyphoplasty. Symptomatic levels were identified by correlating the clinical presentation with conventional radiographs, CT or/and MRI. During the follow up reduction of pain was determined. Radiographic scans were performed pre- and postoperatively and after 3, 6 and 12 months. The vertebral height and endplate angles were measured to assess the restoration of the sagittal alignment. The effects on pain symptoms were measured on a self-reported Visual Analog Scale (VAS) and the Oswestry score was documented. RESULTS: The median pain scores (VAS) decreased significantly for kyphoplasty and vertebroplasty from pre- to post-treatment, as did the Oswestry score (p < 0.05). No significant differences could be found between both groups for the median pain score (VAS) and the Oswestry score. Kyphoplsty led to a significant restoration of the vertebral height and reduction of kyphosis (p < 0.05). During the 1-year follow up both operation techniques were able to stabilize the height of the vertebral body. CONCLUSION: Kyphoplasty and vertebroplasty are effective minimally invasive procedures for the stabilization of osteoporotic vertebral fractures leading to a statistically significant reduction in pain. Kyphoplasty restores significantly vertebral body height in fresh fractures. The restoration of vertebral height and reduction of kyphosis may have an influence on the long term clinical outcome. This has to be evaluated in a long term prospective study.

Aged↗
PubMed2005

Consideration of ergonomic aspects in the development of a new endoscopic navigation system.

During the development of new navigation systems, the ergonomic aspects of the accompanying software are seldom taken into account. The VN system is a navigation system working with real and previously stored neuroendoscopic images. The latter enable the module to execute virtual back movement, e.g. in case of bleeding. Several other modules are offered. The aim of the study was the ergonomic analysis of different modules and their learning curves in cadaveric heads. The endoscope was navigated by the neurosurgeon while another person operated the computer. A total of 128 experiments were performed with two software versions. When the landmark tracking module was used, a real learning curve could be observed. By contrast, testing the measurement module did not produce a learning curve. A significant reduction of the time required by the three modules investigated could be observed with software version 2. The module for virtual back movement works best with a minimum time of 20 s for image storage. During machine-human interactions ergonomic software use is important, especially if operative procedures are performed.

Clinical Competence↗
PubMed2005

Correlation between mitotic delay and aberration burden, and their role for the analysis of chromosomal damage.

The aim was to investigate further the relationship between radiation-induced mitotic delay and the expression of chromosome damage in V79 cells. Recently published data on the time-course of chromosome aberrations in V79 first-cycle metaphases after exposure to 10.4 MeV u(-1) Ar ions (LET = 1226 keV microm(-1)) were supplemented and reanalysed. A statistical analysis of the distribution of aberrations among cells was performed. Furthermore, cells were grouped into subpopulations carrying 0, 1 -2, 3-4, 5- 6 and 7 or more aberrations. Then, based on the mitotic index, the flux of each subgroup through the first mitosis was determined and the average entrance time to mitosis was estimated. For comparison, the flux of aberrant V79 cells generated by X-irradiation was analysed. Analysis of the Ar ion data revealed that the flux of each subpopulation through the first mitosis is strongly affected by its aberration burden, i.e. a positive correlation between the mitotic delay and the number of aberrations carried by a cell was observed. The distribution of aberrations among cells could be well described by Neyman-type A statistics; the corresponding fit parameters also reflect the damage-dependent mitotic delay. Interestingly, comparison of the flux of Ar ion and X-ray-irradiated V79 cells through mitosis revealed (1) that a direct correlation exists between the number of aberrations carried by a cell and its average entrance time to mitosis, and (2) that this effect is independent of the linear energy transfer. The role of these observations for radiation cytogenetics is discussed.

Animals↗
PubMed2005

Treatment of gully pot liquor containing heavy metals with constructed wetlands in Scotland.

The aim of this investigation was to assess the treatment efficiencies for gully pot liquor of 12 experimental vertical-flow constructed wetland filters containing Phragmites australis (Cav.) Trin. ex Steud. (Common Reed) and filter media of different adsorption capacities in a cold climate. Seven of the twelve filters received inflow water spiked with heavy metals. For one year, hydrated copper nitrate and hydrated nickel nitrate were added to sieved gully pot liquor to simulate contaminated primary treated storm water runoff. The inflow concentrations for dissolved copper, nickel and nitrate-nitrogen were approximately 1.0, 1.0 and 1.45 mg/l, respectively, which represent mean loading rates of 0.063 g/m2/d for Filters 2 and 7 to 11, and 0.115 g/m2/d for Filter 12. For these filters receiving metals, an obvious breakthrough of dissolved nickel was recorded after road gritting and salting during winter. Sodium chloride was responsible for nickel leaching. Reductions of copper, nickel, biochemical oxygen demand and suspended solids were frequently insufficient compared to international secondary wastewater treatment standards. Moreover, the overall filtration performance for all filters was similar.

Climate↗