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Biomedical subjects

L Heuser

Publications and source records attributed to L Heuser.

At least 37 records · Page 2Linked to original sources
PubMed1998

Perfusion CT of the brain: diagnostic approach for early detection of ischemic stroke.

PURPOSE: To determine the value of perfusion computed tomography (CT) in a clinical study of patients with stroke and compare the results with single photon emission CT (SPECT) findings. MATERIALS AND METHODS: Perfusion CT was performed within 6 hours of symptom onset in 32 patients with possible stroke. Cerebral blood volume (CBV), cerebral blood flow (CBF), and time to peak contrast material enhancement were calculated on the basis of the CT results. Cerebral SPECT was also performed in a subgroup of 18 patients. Perfusion CT and SPECT findings were compared in a lesion-by-lesion analysis. Perfusion CT results were compared with follow-up CT and magnetic resonance imaging findings. RESULTS: Areas of reduced CBF were detected with the aid of perfusion CT in 25 of 28 patients with a proved infarct (sensitivity, 89%). The results of the CBF maps corresponded well to SPECT findings in 13 (81%) of 16 patients, but ischemia was located outside the scanning level in the other three patients and was therefore missed. Perfusion CT revealed various changes in CBF, CBV, and time to peak enhancement in ischemic territories. CONCLUSION: Perfusion CT not only allows early detection of cerebral ischemia but also yields valuable information about the extent of perfusion disturbances.

Adult↗
PubMed1998

[Vascular imaging with magnetic resonance angiography (MRA)].

Magnetic resonance angiography (MRA) has become firmly established within the scope of diagnostic imaging procedures for assessing many pathological conditions and, depending on the questions posed, is often used on its own or as a supplementary method. MRA allows the (non)-invasive visualization of the vasculature by using the effects of moving spins on the magnetic resonance signal. MRA techniques can be classified into two different techniques depending on how the contrast is achieved: Time-of-flight (TOF) and phase contrast (PC) methods. Both methods have advantages and limitations as an imaging technique. This article outlines the basic understanding of MRA as well as the recent rapid expansion in MRA acquisition and processing techniques.

Contraindications↗
PubMed1997

Impaired episodic memory retrieval in a case of probable psychogenic amnesia.

A patient with severe, selective retrograde amnesia for personal material diagnosed as probable psychogenic amnesia, was investigated intensively neuropsychologically with cranial computed tomography (CCT), magnetic resonance imaging (MRI), and single photon emission tomography (SPECT). The patient was of average intelligence and memory with no anterograde amnesia. No evidence for structural brain damage was detected in CCT and MRI. SPECT, performed about 3 weeks after the onset of symptoms, demonstrated reduced perfusion in right temporal and frontal areas, that is, in areas which have been suggested as critical for episodic memory retrieval. To study episodic memory retrieval, positron-emission-tomography (PET) blood flow (rCBF) measurements were performed 6 months after the onset of symptoms. During episodic memory retrieval bilateral neuronal activations were observed in the precuneus, the lateral parietal and the right dorsolateral and polar prefrontal cortex. Compared to the results of previous functional imaging studies on episodic memory retrieval, our findings suggest an underlying functional disturbance of brain areas previously demonstrated to be involved in episodic memory retrieval.

Adult↗
PubMed1997

[CAD/CAM (computer-aided design/computer-aided manufacturing) titanium implants for cranial and craniofacial defect reconstruction].

The reconstruction of craniofacial bone defects with intraoperatively modeled prosthesis restricts the choice of material and its biocompatibility and the prediction of the esthetic result. A prolonged duration of the surgical procedure and an increased stress on the patient are consequences. In contrast, modern industrial CAD/CAM-systems allow the prefabrication of titanium prosthesis: An individual computer-based 3D model of the bony defect is generated after acquisition, transfer and evaluation of helical CT data. Basing on these data the individual prosthesis-shape is designed using freeform surfaces geometries and fabricated by a numerically controlled milling machine. The conical margins of this prosthesis-geometry are generated by the borders of the defect with a minimal gap of 0.25 mm, and the surface contours by considering the non-affected neighbouring contours with a constant thickness of 1.5 mm. Individual osteosynthesis-microplates for fixation are integrated in design and manufacturing if screw-holes cannot be integrated in the thin margins of the implants. The radiological and clinical results of 17 patients after reconstruction of craniofacial bone defects with CAD/CAM titanium implants were good. Complications were not observed.

Adolescent↗
PubMed1996

[3-D-TONE magnetic resonance angiography in the detection of intracranial aneurysms compared with digital subtraction angiography. A prospective study].

PURPOSE: To evaluate the efficiency and accuracy of the optimized 3-D-MT-TONE-magnetic resonance angiography (MRA) with that of intraarterial digital subtraction angiography (DSA) in the detection of intracranial aneurysms. MATERIAL AND METHODS: From March 1994 to March 1995 30 patients with 38 aneurysms were prospectively subjected to MRA as well as to DSA. Respiratory insufficient patients were excluded from MRA. RESULTS: The aneurysm size ranged from 3-50 mm with an average size of 9 mm. Correct diagnosis was done in 33 aneurysms (86.8%) in 26 of the patients. In 4 patients (13.3%) with 5 aneurysms, the blinded readers made an incorrect diagnosis due to degradation of image quality. One (2.6%) aneurysm was falsely described via MRA as well as via DSA. The sensitivity was 86.8%. In the control group of 30 patients three aneurysms were found, therefore the specificity was 90% and we could calculate a positive predictive value of 97.1%, a negative predictive value of 84.4% and a correct diagnosis of 90.1%. CONCLUSION: Our results show that MT-TONE-MRA is a useful non-invasive technique with improved vascular detail and vascular background for detection of intracranial aneurysm. Further technical improvements are necessary for better visualisation of pathological findings in the carotid siphon, where only 60% of the aneurysms could be clearly detected.

Adult↗
PubMed1996

MIN-biopsy of brain tumors: operative technique and histomorphological results.

MIN-biopsy is defined as an open minimal invasive biopsy, performed by microsurgical principles over a small osteoplastic trepanation or bore hole. Localization of the lesion is performed by exact calculation using the CT-topogram. Between 1993 and 1995 ten patients with unknown intracranial lesions were operated using the MIN-biopsy approach. Age ranged between 36 to 84 years (median age 57.8 years). Patients included five females and five males. Histomorphological diagnosis was possible in all cases. Histological diagnoses were glioblastoma multiforme in three patients and B-cell malignant lymphoma in four cases. Anaplastic astrocytoma was found in one case and the diagnosis of metastatic adenocarcinoma was observed in two patients. Complications or neurological deterioration were not observed. MIN-biopsy seems to be a safe procedure to arrive at exact neuropathological diagnosis of brain tumors. The procedure is compared with the established method of stereotactic biopsy by review of the literature.

Adult↗
PubMed1995

CT data acquisition as a basis for modern diagnosis and therapy in maxillofacial surgery.

More than 20 years after its introduction computed tomography has become a routine method in the diagnostic work-up of traumatic and neoplastic disorders in maxillofacial surgery. Short acquisition times of 1 sec per image reduce motion artifacts and permit increased numbers of patient examinations. Different reconstruction algorithms allow specific evaluation of either osseous or soft tissue structures. By adjusting window center and window width the 2048 attenuation values can be transformed into the visible gray scale. Single sequential slices--as employed in routine diagnosis of tumor patients--still yield the highest image quality. Fast volume data acquisition associated with spiral scanning proves to be of special benefit in trauma patients. The resulting data set can be used for reconstruction of single slices, 2-dimensional (2D) reformated images in all planes and 3D surface rendering.

Artifacts↗
PubMed1995

Prefabricated prostheses for the reconstruction of skull defects.

Cranioplasties using intraoperatively modeled prostheses may fail to create harmonic contours with long-term stability. In contrast, preoperative modeling would allow more sophisticated planning of the contour and better preparation of the implant material, if a sufficiently precise model of the defect-site was available. In this respect, computer aided design and manufacturing (CAD/CAM)-techniques based on helical computed tomography (CT) data are successfully used for the prefabrication of prostheses: An individual computer-based 3-dimensional model of the bony defect is generated after acquisition, transfer and evaluation of the CT data; from this freeform surfaces geometry an individual and "idealized" prosthesis-geometry is derived and fabricated by a numerically controlled milling machine using modern industrial CAD/CAM-systems and design software. The margins of this prosthesis-geometry are generated by the borders of the defect and the surface by considering the non-affected neighbouring contours. Cranioplasties in cases of large postsurgical skull defects are presented as the first clinical applications of this new method, which also allows the use of titanium and fabrication of integrated fixation-devices.

Computer Simulation↗
PubMed1995

Reconstruction of craniofacial bone defects with individual alloplastic implants based on CAD/CAM-manipulated CT-data.

Reconstruction of craniofacial bone defects by intraoperative modelling of autogenous or alloplastic materials may cause undesirable results concerning the implant shape or the long-term maintenance of this shape. Furthermore, the use of alloplastic materials to be modelled intraoperatively may result in an inflammatory tissue response. Therefore the question is raised whether CAD/CAM-techniques may be used for the pre-operative geometric modelling of the implant based on helical computed tomography data. A numerically based 3-dimensional model of the skull defect serves as the basis for a freeform-surfaces design of the implant shape, position and thickness, using modelling tools and programmes developed for industrial CAD/CAM. The precise and individual fit of the implant results from generating its margins by the borders of the defect, whereas the implant surface is generated by the geometry of the non-affected neighbouring bone contours. The implant data run a numerically controlled milling machine to fabricate the individual implant. The reconstruction of post-traumatic defects of the forehead, of post-surgical temporal defects after intracranial haemorrhage, and of a parieto-occipital defect due to ablative tumour surgery are presented as the first clinical experiences of this new method.

Adolescent↗
PubMed1995

[Dysphagia: a neurosurgical indication for an operation?].

Ventral osteophytes of the cervical spine can be the reason for dysphagia in rare cases. We present a 67-year old man with difficulties in swallowing for three years and a ventral osteophyte at the level of C 5/6. Native X-rays of the cervical spine, CT-scan and x-ray examination with barium meal and with a barium ball was performed. In our case the most useful procedure for operative indication was the dynamic examination with the barium ball which demonstrates clearly the obstructed oesophageal passage. During operation the ventral osteophyte was resected via ventral approach to the cervical spine. Postoperatively patient's symptoms completely disappeared. Differential diagnosis and therapy are discussed.

Aged↗
PubMed1994

The amygdala's contribution to memory--a study on two patients with Urbach-Wiethe disease.

The consequences of primary amygdaloid damage on memory performance are described in terms of neuropsychological, CT, MRI and PET results of two patients, a brother and a sister. Both had circumscribed, bilaterally symmetrical damage confined to the amygdaloid region, while the hippocampal formation and other brain structures were intact. PET-imaging furthermore revealed an overall decrease in glucose metabolism which was particularly apparent at the cingular and thalamic levels. Although neither patient was amnesic, both showed memory impairments in selective tests. In one patient these impairments were more pronounced and they were accompanied by marked affective-emotional fluctuations. Our results suggest that the amygdaloid region is a bottle-neck structure that confers an affective flavour to memories, thereby enhancing the probability of their long term storage.

Adult↗
PubMed1994

In vivo study of online liver tissue classification based on envelope power spectrum analysis.

An ultrasonic imaging and signal analysis system, combining a 3.5 MHz linear array B-scanner and an array processor, has been realized for a clinical liver tissue classification study. Based on the complete unprocessed rf data set of a real time B-image, local envelope power spectra averaged over interactively defined regions are computed. These spectra are partially corrected for several tissue type independent effects that affect comparability. A library containing the in vivo data of 65 patients with known liver tissue states in three groups (normal, cirrhotic, fat) was built up. An algorithm based on numerical optimization of parametrized spectrum characteristics combined with a k-nearest-neighbors classifier, applied to the library, leads to correct classification rates of 85.8 to 87.5 percent in discriminating pathological from normal tissue states. The method can be used for k-weighted color coded tissue type imaging with acceptable spatial resolution.

Algorithms↗
PubMed1992

Random digit dialing: the potential effect on sample characteristics of the conversion of nonresidential telephone numbers.

This study examined the changes over time in the residential status of telephone numbers and the characteristics of households with telephone numbers that changed from nonresidential to residential. The authors determined the status in 1987 of all phone numbers (n = 9,107) that had been found to be nonresidential in six case-control studies conducted between 1979 and 1986 in Washington State. A telephone interview to obtain information on household characteristics was completed for 1,333 of the 1,901 phone numbers that had become residential by 1987. The interviews revealed that households with phone numbers that had previously been nonresidential differed from the general population with respect to household income, the age of household members, and the education of the head of the household. Data for the same area showed that the proportion of all phone numbers that were residential changed differentially according to the prefix (which roughly defines geographic area) during a 12-month period between 1987 and 1988, with some prefixes showing increases in residential phone numbers of more than 20%, while other prefixes decreased or stayed the same over the same period. We conclude that methods of random digit dialing that use two-stage designs or exclude previously dialed numbers may result in biased sampling unless changes over time are considered.

Adolescent↗