Biomedical subjects

Herwig Imhof

Publications and source records attributed to Herwig Imhof.

14 recordsLinked to original sources

PubMed2007

CT-MR image data fusion for computer assisted navigated neurosurgery of temporal bone tumors.

PURPOSE: To demonstrate the value of multi detector computed tomography (MDCT) and magnetic resonance imaging (MRI) in the preoperative work up of temporal bone tumors and to present, especially, CT and MR image fusion for surgical planning and performance in computer assisted navigated neurosurgery of temporal bone tumors. MATERIALS AND METHODS: Fifteen patients with temporal bone tumors underwent MDCT and MRI. MDCT was performed in high-resolution bone window level setting in axial plane. The reconstructed MDCT slice thickness was 0.8 mm. MRI was performed in axial and coronal plane with T2-weighted fast spin-echo (FSE) sequences, un-enhanced and contrast-enhanced T1-weighted spin-echo (SE) sequences, and coronal T1-weighted SE sequences with fat suppression and with 3D T1-weighted gradient-echo (GE) contrast-enhanced sequences in axial plane. The 3D T1-weighted GE sequence had a slice thickness of 1mm. Image data sets of CT and 3D T1-weighted GE sequences were merged utilizing a workstation to create CT-MR fusion images. MDCT and MR images were separately used to depict and characterize lesions. The fusion images were utilized for interventional planning and intraoperative image guidance. The intraoperative accuracy of the navigation unit was measured, defined as the deviation between the same landmark in the navigation image and the patient. RESULTS: Tumorous lesions of bone and soft tissue were well delineated and characterized by CT and MR images. The images played a crucial role in the differentiation of benign and malignant pathologies, which consisted of 13 benign and 2 malignant tumors. The CT-MR fusion images supported the surgeon in preoperative planning and improved surgical performance. The mean intraoperative accuracy of the navigation system was 1.25 mm. CONCLUSION: CT and MRI are essential in the preoperative work up of temporal bone tumors. CT-MR image data fusion presents an accurate tool for planning the correct surgical procedure and is a benefit for the operational results in computer assisted navigated neurosurgery of temporal bone tumors.

Adult↗

PubMed2006

MR imaging of the cervical spine: assessment of image quality with parallel imaging compared to non-accelerated MR measurements.

To compare the quality of cervical spine MR images obtained by parallel imaging [generalized autocalibrating partially parallel acquisition (GRAPPA)] with those of non-accelerated imaging, we conducted both phantom studies and examinations of ten volunteers at 1.5Tesla with a dedicated 12-element coil system and a head-spine-neck coil combination. Acquisitions included axial T2-weighted (T2w) images with both methods, and sagittal T2w and T1w images in vivo with the latter coil combination. Non-accelerated MRI with two averages and GRAPPA (acceleration factor 2) with two averages (GRAPPA/2AV, time reduction of approximately 50%) and four averages (GRAPPA/4AV) were compared. In the phantom, the signal-to-noise ratio of the GRAPPA/2AV was lower than that of the other two settings. In vivo, the image inhomogeneity (non-uniformity, NU) was significantly higher in T2w GRAPPA/2AV than in both other settings, and in T1w GRAPPA/2AV compared to GRAPPA/4AV. Subjectively, the delineation of anatomical structures was sufficient in all sequences. Only the spinal cord was considered to be better delineable on the non-accelerated T1w sequence compared to GRAPPA/2AV. In part, GRAPPA/4AV performed better than the other settings. The subjective image noise was lowest with GRAPPA/4AV. In cervical spine MRI, the examination time can be reduced by nearly 42% with GRAPPA, while preserving sufficient image quality.

Cervical Vertebrae↗

PubMed2006

Advances in musculoskeletal radiology: multidetector computed tomography.

The clinical potential of multidetector CT is significantly increased because of the possibility of almost instantaneous isotropic reformations in all planes, increased speed and coverage, and easy interpretation. Multidetector CT has a significant role in the correct and quick diagnosis and treatment of emergency department patients. In complex anatomic regions, it is an important diagnostic aid, and it allows exact classification of the bony lesion, which is important for diagnosis, treatment, and prognosis. Multidetector CT visualizes congenital deformities and is useful in oncology. Ongoing developments comprise diagnosis and treatment, preoperative and postoperative planning, and hard-ware imaging. Relatively new but well-known applications of multidetector CT include intraoperative navigation, implant and prosthesis planning and surgery simulation, vertebroplasty, and pedicle screw installations.

Arthroplasty, Replacement, Hip↗

PubMed2006

MDCT versus digital radiography in the evaluation of bone healing in orthopedic patients.

OBJECTIVE: Assessment of bone healing in orthopedic patients is usually monitored by radiographs in two views. The purpose of our study was to compare multiplanar reconstructions from MDCT data sets with digital radiographs for assessing the extent of bone healing. MATERIALS AND METHODS: Forty-three orthopedic patients (19 women, 24 men) who underwent MDCT and radiography after arthrodesis, fractures, or spinal fusions were included in our study. MDCT was performed on an MX 8000IDT scanner and served as the gold standard. The technical parameters were adapted to the anatomic region. A bone algorithm for reconstruction was used (3,500/600 H). Multiplanar reconstructions were calculated in two orthogonal planes. All patients underwent digital radiography on a Multix FD system in two views according to standard procedures. Multiplanar reconstructions and radiographs were analyzed by two musculoskeletal radiologists in a consensus interpretation to determine bone healing using a semiquantitative approach. RESULTS: In 27 patients (63%), MDCT and digital radiography were concordant with regard to the extent of bone healing, whereas in 16 patients (37%) the results were not concordant. In eight patients (19%) digital radiographs underestimated the extent of bone healing, whereas in another eight patients (19%) they overestimated the degree of fusion. CONCLUSION: MDCT using high-quality 2D reformatting is recommended as the primary imaging technique for the evaluation of bone healing.

Female↗

PubMed2005

White matter hyperintensities and chronicity of depression.

OBJECTIVE: White matter hyperintensities (WMHs) on T(2)-weighted magnetic resonance imaging (MRI) of the brain are associated with advanced age and late-life depression. Most investigations predominantly found these lesions in frontal lobe and basal ganglia supporting the hypothesis of a fronto-striatal dysfunction in depression. A prospective study was undertaken to investigate the association between extent of WMHs and clinical outcome in elderly depressed patients. METHODS: Thirty-one non-demented depressed subjects underwent a 1.5 T cranial MRI scan. The MRI scans were analysed in consensus by two experienced radiologists. Each MRI scan was assessed for presence and extent of WMHs, which are differentiated in periventricular hyperintensities (PVHs) and deep white matter hyperintensities (DWMHs). A total of 21 patients of the original cohort of 31 patients were re-assessed 5 years after baseline assessment. We ascertained the severity of depressive symptoms, the longitudinal course of depression, the cognitive decline and the global assessment of functioning at follow-up visit. RESULTS: (1) Subjects with greater extent of WMHs had a significant higher Hamilton Depression Rating Scale (HAM-D) score, (2) had more severe longitudinal courses of depression (3) and had a lower Mini-Mental State Examination (MMSE) score. CONCLUSIONS: WMHs on MRI are associated with poorer outcome in elderly depressed subjects. Further studies are needed to evaluate WHMs as prognostic factor for an appropriate treatment decision-making.

Aged↗

PubMed2004

Dental CT and orthodontic implants: imaging technique and assessment of available bone volume in the hard palate.

PURPOSE: Palatal implants (PI) have been introduced for orthodontic treatment of dental and skeletal dysgnathia. Due to the restricted amount of bone in this region, precise preoperative anatomic information is necessary. The aim of this study was to determine whether dental CT could serve as a tool to locate the optimal size and position for orthodontic implant placement. MATERIALS AND METHODS: In 32 patients, where palatal implant placement was planned, axial CT scans of the maxillary bone were acquired. Using a standard dental software package (Easy Vision dental software package 2.1, Philips; Best, The Netherlands), paracoronal views were reconstructed and measurements of palatal bone height in 3 mm increments, dorsally from the incisive canal, were performed in the median and both paramedian regions. RESULTS: The overall mean bone height was 5.01 mm (S.D. 2.60), ranging from 0 to 16.9 mm. The maximum palatal bone height was 6.17 mm (S.D. 2.81) at 6 mm dorsally from the incisive canal. Due to the lack of adequate bone (less than 4 mm), implant placement was not performed in 3 cases (7%). In the remaining 39 cases (93.0%), primary implant stability was achieved and complications, such as perforation of the palate, could be avoided. CONCLUSION: The results demonstrate that dental CT promises to be a valuable tool in evaluating the potential and optimal size and site for orthodontic implant placement.

Adolescent↗

PubMed2004

Definition of pertinent parameters for the evaluation of articular cartilage repair tissue with high-resolution magnetic resonance imaging.

To evaluate articular cartilage repair tissue after biological cartilage repair, we propose a new technique of non-invasive, high-resolution magnetic resonance imaging (MRI) and define a new classification system. For the definition of pertinent variables the repair tissue of 45 patients treated with three different techniques for cartilage repair (microfracture, autologous osteochondral transplantation, and autologous chondrocyte transplantation) was analyzed 6 and 12 months after the procedure. High-resolution imaging was obtained with a surface phased array coil placed over the knee compartment of interest and adapted sequences were used on a 1 T MRI scanner. The analysis of the repair tissue included the definition and rating of nine pertinent variables: the degree of filling of the defect, the integration to the border zone, the description of the surface and structure, the signal intensity, the status of the subchondral lamina and subchondral bone, the appearance of adhesions and the presence of synovitis. High-resolution MRI, using a surface phased array coil and specific sequences, can be used on every standard 1 or 1.5 T MRI scanner according to the in-house standard protocols for knee imaging in patients who have had cartilage repair procedures without substantially prolonging the total imaging time. The new classification and grading system allows a subtle description and suitable assessment of the articular cartilage repair tissue.

Adult↗

PubMed2004

Limited diagnostic agreement of quantitative sonography of the radius and phalanges with dual-energy x-ray absorptiometry of the spine, femur, and radius for diagnosis of osteoporosis.

OBJECTIVE: The aim of our study was to evaluate the diagnostic agreement of quantitative sonography of the radius and proximal phalanx and dual-energy X-ray absorptiometry (DXA) of the radius, lumbar spine, and femoral neck for the detection of osteoporosis. MATERIALS AND METHODS: In 95 women (mean age, 53 +/- 13 years) and 26 men (mean age, 53 +/- 13 years), DXA measurements of the lumbar spine (posterior-anterior, L1-L4) and the femoral neck, as well as quantitative sonography of the radius and proximal phalanx of the third finger were obtained. The percentage of patients below a given threshold was calculated for each imaging technique. A T score of less than -2.5 indicated presence of osteoporosis. Diagnostic agreement in identifying individuals with osteoporosis was assessed using kappa scores. RESULTS: Between 14% and 22% of the patients were classified as osteoporotic after DXA of the various regions of interest of the radius, 31% after DXA of the spine, 43% after DXA of the femoral neck, 32% after quantitative sonography of the distal radius, and 34% after quantitative sonography of the phalanx of the third finger. Correlation coefficients between T values for quantitative sonography and those for DXA varied between not significant and 0.54 at the different regions. Kappa analysis showed the diagnostic agreement among quantitative sonography and DXA to be fair to moderate (kappa = 0.38-0.48). The highest agreement was between quantitative sonography of the proximal phalanx of the third finger and DXA of the total radius (kappa 0.48; p < 0.05). CONCLUSION: Considerable diagnostic disagreement exists between quantitative sonography and DXA of the forearm, as is true for most quantitative techniques in the assessment of skeletal status. The lack of correlation makes quantitative sonography impractical for routine diagnostic use but might characterize different parameters related to bone quality.

Absorptiometry, Photon↗

PubMed2003

Computer-enhanced stereoscopic vision in a head-mounted operating binocular.

Based on the Varioscope, a commercially available head-mounted operating binocular, we have developed the Varioscope AR, a see through head-mounted display (HMD) for augmented reality visualization that seamlessly fits into the infrastructure of a surgical navigation system. We have assessed the extent to which stereoscopic visualization improves target localization in computer-aided surgery in a phantom study. In order to quantify the depth perception of a user aiming at a given target, we have designed a phantom simulating typical clinical situations in skull base surgery. Sixteen steel spheres were fixed at the base of a bony skull, and several typical craniotomies were applied. After having taken CT scans, the skull was filled with opaque jelly in order to simulate brain tissue. The positions of the spheres were registered using VISIT, a system for computer-aided surgical navigation. Then attempts were made to locate the steel spheres with a bayonet probe through the craniotomies using VISIT and the Varioscope AR as a stereoscopic display device. Localization of targets 4 mm in diameter using stereoscopic vision and additional visual cues indicating target proximity had a success rate (defined as a first-trial hit rate) of 87.5%. Using monoscopic vision and target proximity indication, the success rate was found to be 66.6%. Omission of visual hints on reaching a target yielded a success rate of 79.2% in the stereo case and 56.25% with monoscopic vision. Time requirements for localizing all 16 targets ranged from 7.5 min (stereo, with proximity cues) to 10 min (mono, without proximity cues). Navigation error is primarily governed by the accuracy of registration in the navigation system, whereas the HMD does not appear to influence localization significantly. We conclude that stereo vision is a valuable tool in augmented reality guided interventions.

Depth Perception↗

PubMed2003

Olfaction and depth of word processing: a magnetoencephalographic study.

Using a whole-cortex magnetoencephalograph, magnetic field changes were recorded to describe brain activities related to simultaneous visual and olfactory processing and to detect odor-related influences on verbal information processing. Words had to be either shallowly (nonsemantic) or deeply (semantic) encoded by healthy young subjects, each of these tasks under two different kinds of olfactory stimulation. After each encoding phase, word recognition performance was tested. First, the odor was randomly associated with some of the study words (simultaneous stimulation; same duration as for words) for both depths of word processing conditions, and second, continuous olfactory stimulation (permanent stimulation) was provided during the whole study phases of both depths of word processing conditions. The statistical analysis of the physiological data revealed evidence of a specific odor-induced effect depending on depth of word processing and kind of olfactory stimulation. Brain activity between about 250 and 450 ms as well as between about 650 and 1000 ms after stimulus onset was found to vary as a function of odor delivery and depth of word processing. In addition, a significant effect of odor stimulation on subsequent word recognition performance occurred in case of simultaneous odor stimulation and semantic word encoding. It is interpreted that in this case, word recognition performance significantly decreased because of the presence of the odor during prior word encoding. Such a behavioral effect was missing in all other conditions. The present psychological and physiological findings support the idea that semantic word encoding is specifically affected by simultaneous olfactory information processing. It is concluded that this phenomenon is due to a competition with cortical regions related to language and olfactory information processing, as suggested by T. S. Lorig (1999, Neurosci. Biobehav. Rev. 23, 391-398).

Adult↗

PubMed2003

Olfaction and face encoding in humans: a magnetoencephalographic study.

Magnetic field changes were recorded while 20 healthy young participants performed a deep face encoding task. Some of the faces were randomly associated with a simultaneously presented odor. A recognition test, during which all faces were presented again together with the same number of new faces, followed. The task was to discriminate between repeated and new faces. During the recognition test no odor was presented. The recognition performance was significantly influenced by the simultaneously associated odor during the encoding phase. Faces associated with odor were less accurately recognized. In addition, we found significant physiological differences between 'encoded faces without odor' and 'encoded faces with odor'. In particular, two effects occurred. Between about 200 and 300 ms after stimulus onset 'encoded faces without odor' evoked higher brain activity than 'encoded faces with odor'. Between about 600 and 900 ms after stimulus onset 'encoded faces with odor' evoked higher brain activity than 'encoded faces without odor'. Whereas the latter effect is interpreted as reflecting conscious olfactory information processing, the earlier effect is suggested to reflect an odor influence on face encoding. We suggest that the simultaneous odor association distracted face encoding resulting in a significantly reduced recognition performance. These findings are suggested to represent evidence of multimodal sensoric interactions between visual face processing and olfactory information.

Adult↗

PubMed2002

Computer-enhanced stereoscopic vision in a head-mounted display for oral implant surgery.

We developed a head-mounted display (HMD) with integrated computer-generated stereoscopic projection of target structures and integrated it into visit, a specific oral implant planning and navigation software. The HMD is equipped with two miniature computer monitors that project computer-generated graphics stereoscopically into the optical path. Its position is tracked by the navigation system's optical tracker and target structures are displayed in their true position over the operation site. In order to test this system's accuracy and spatial perception of the viewer, five interforaminal implants in three dry human mandibles were planned with visit and executed using the stereoscopic projection through the HMD. The deviation between planned and achieved position of the implants was measured on corresponding computed tomography (CT) scan images recorded post-operatively. The deviation between planned and achieved implant position at the jaw crest was 0.57 +/- 0.49 mm measured from the lingual, and 0.58 +/- 0.4 mm measured from the buccal cortex. At the tip of the implants the deviation was 0.77 +/- 0.63 mm at the lingual and 0.79 +/- 0.71 mm at the buccal cortex. The mean angular deviation between planned and executed implant position was 3.55 +/- 2.07 degrees. The present in vitro experiment indicates that the concept of preoperative planning and transfer to the operative field by an HMD allows us to achieve an average precision within 1 mm (range up to 3 mm) of the implant position and within 3 degrees deviation for the implant inclination (range up to 10 degrees ). Control during the drilling procedure is significantly improved by stereoscopic vision through the HMD resulting in a more accurate inclination of the implants.

Computer Graphics↗

PubMed2002

Vertebral metastases: assessment with apparent diffusion coefficient.

The authors evaluated the apparent diffusion coefficient (ADC) in the assessment of vertebral metastases and acute vertebral compression fractures in 22 patients with known or suspected vertebral metastases. On the basis of significantly (P <.03) different ADCs, vertebral metastases (0.69 x 10(-3) mm2/sec) and pathologic compression fractures (0.65 x 10(-3) mm2/sec) can be safely distinguished from vertebral bodies (1.66 x 10(-3) mm2/sec) and benign compression fractures (1.62 x 10(-3) mm2/sec). Thus, the use of ADCs may increase the specificity of magnetic resonance imaging in these patients.

Echo-Planar Imaging↗

PubMed2001

Guidelines and algorithms: strategies for standardization of referral criteria in diagnostic radiology.

Guidelines can be regarded as special forms of algorithms and have been shown to be useful tools for supporting medical decision making. With the Council Directive 97/43/Euratom recommendations concerning referral criteria for medical exposure have to be implemented into national law of all EU member states. The time- and cost-consuming efforts of developing, implementing, and updating such guidelines are balanced by the acceptance in clinical practice and eventual better health outcomes. Clearly defined objectives with special attention drawn on national and regional differences among potential users, support from organisations with expertise in evidence-based medicine, separated development of the evidence component and the recommendations component, and large-scale strategies for distribution and implementation are necessary. Editors as well as users of guidelines for referral criteria have to be aware which expectations can be met and which cannot be fulfilled with this instrument; thus, dealing with guidelines requires a new form of "diagnostic reasoning" based on medical ethics.

Algorithms↗