Biomedical subjects

Fritz Schick

Publications and source records attributed to Fritz Schick.

64 records · Page 4Linked to original sources

PubMed2003

[Artifacts in MRT caused by instruments and implants].

Metallic instruments and implants can cause severe image artifacts in magnetic resonance imaging (MRI). Besides the properties of the materials and the geometrical arrangement of the devices, the applied MRI sequence type and its parameters (echo time, voxel size, read-out bandwidth, orientations of encoding directions, etc.) play also an important role. These interactions are presented in a systematic survey. A detailed description of the basic physical mechanisms underlying the generation of artifacts is also provided.

Artifacts↗

PubMed2003

In vivo efficiency of four commercial monopolar radiofrequency ablation systems: a comparative experimental study in pig liver.

RATIONALE AND OBJECTIVES: To evaluate the efficiency of 4 radiofrequency (RF) systems by assessing the amount of delivered energy for each thermal induced lesion after perfusion mediated RF ablation and to compare the influence of perfusion mediation types on the energy efficiency. METHODS: A total of 43 ablations in 16 male landrace pigs with 4 RF devices were performed strictly according to the manufacturers' instructions. Total absorbed energy was computed and then related to 3D volumetry obtained after histopathological evaluation. Sixteen ablations were performed under physiological liver perfusion and 27 ablations with occlusion of portal vein, hepatic artery, or both vessels. Energy efficiency values of the RF systems for different vascular occlusion techniques were compared and analyzed by a nonparametrical rank sum test. RESULTS: Under physiological perfusion, the average energy delivered to produce 1-cm3 lesion size was calculated to 1650 +/- 929, 3097 +/- 389, 8312 +/- 2068, and 5493 +/- 2306 Watt x s/cm3 for the Berchtold, Radionics, Radiotherapeutics, and RITA system, respectively. After perfusion-mediated RF ablation, artery occlusion was not as effective as portal vein occlusion, which reduced the energy to 587 +/- 148, 869 +/- 276, and 903 +/- 394 Watt. s/cm3 for the Berchtold, Radionics, and Radiotherapeutics system, respectively. The occlusion of vessels, portal vein, and artery or portal vein alone increased the energy efficiency compared with physiological liver perfusion or occlusion of the artery (P = 0,003). CONCLUSIONS: Under physiological liver perfusion the open perfused system and the internally cooled system provided the best efficiency values with lowest standard deviations. The energy efficiency was increased markedly for all systems after occlusion of the portal vein either alone or in combination with arterial occlusion. Occlusion of the hepatic artery did not improve the efficiency.

Animals↗

PubMed2003

Inductively coupled rf coils for examinations of small animals and objects in standard whole-body MR scanners.

Inductively coupled solenoid coils fitting to objects in the size of mice or rats were developed to adapt modem whole-body MR scanners featuring sufficient gradient strength for animal examinations with high spatial resolution. Homogenous receiver characteristics is achievable over almost the whole inner region of the solenoid coils. The SNR can be increased by a factor 2 to 6 with the adapting coils for examinations using the head coil as connected receiver. Standard sequences on clinical 1.5 T scanners can be applied with adapted transmitter voltages. For example, a SNR value of about 30 is achievable in a mouse liver after 10 minutes measuring time using a 2-D spin echo imaging sequence and a size of 0.3 x 0.3 x 0.8 mm3 for the picture elements.

Animals↗

PubMed2003

Intramyocellular lipids: anthropometric determinants and relationships with maximal aerobic capacity and insulin sensitivity.

The existence of metabolically relevant intramyocellular lipids (IMCL) as assessed by the noninvasive (1)H-magnetic resonance spectroscopy (MRS) has been established. In the present studies, we analyzed the relationships between IMCL in two muscle types [the predominantly nonoxidative tibialis muscle (tib) and the predominantly oxidative soleus muscle (sol)] and anthropometric data, aerobic capacity (VO(2)max, bicycle ergometry, n = 77) and insulin sensitivity (hyperinsulinemic euglycemic clamp, n = 105) using regression analysis. In univariate regression, IMCL (tib) was weakly but significantly correlated with percentage of body fat (r = 0.28, P = 0.01), whereas IMCL (sol) was better correlated with waist-to-hip ratio (r = 0.41, P < 0.0001). No significant univariate correlation with age or maximal aerobic power was observed. After adjusting for adiposity, IMCL (tib) was positively correlated with measures of aerobic fitness. A significant interaction term between VO(2)max and percentage of body fat on IMCL (tib) (P = 0.04) existed (whole model r(2) = 0.26, P = 0.001). In contrast, aerobic fitness did not influence IMCL (sol). No correlation between insulin sensitivity as such and IMCL (tib) (r = -0.13, P = 0.2) or IMCL (sol) (r = 0.03, P = 0.72) was observed. Nethertheless, a significant interaction term between VO(2)max and IMCL on insulin sensitivity existed [P = 0.04 (tib) and P = 0.02 (sol)]; [whole model (sol) r(2) = 0.61, P < 0.0001, (tib) r(2) = 0.60, P < 0.0001]. In conclusion, obesity and aerobic fitness are important determinants of IMCL. IMCL and insulin sensitivity are negatively correlated in untrained subjects. The correlation between the two parameters is modified by the extent of aerobic fitness and cannot be found in endurance trained subjects. Thus, measurements of aerobic fitness and body fat are indispensable for the interpretation of IMCL and its relationship with insulin sensitivity.

Adipose Tissue↗

PubMed2003

MR imaging-guided adrenal biopsy using an open low-field-strength scanner and MR fluoroscopy.

OBJECTIVE: The aim of our study was to test the feasibility and specific properties of MR imaging-guided adrenal biopsy using an open 0.2-T scanner and MR fluoroscopic fast imaging with steady-state free precession sequences. CONCLUSION: MR imaging-guided biopsy of the adrenal gland is feasible and safe. In all patients, appropriate specimens were obtained with full diagnostic yield and accuracy. MR fluoroscopy is particularly useful to establish an oblique paravertebral access without pleural transgression. For final needle placement, supplementary breath-hold multislice sequences are required in most cases.

Adrenal Gland Neoplasms↗

PubMed2002

Proton MRS in Kennedy disease: absolute metabolite and macromolecular concentrations.

PURPOSE: To investigate whether glutamine and glutamate (Glx) were elevated in Kennedy Disease (KD), and whether pathological proteins were spectroscopically visible as altered macromolecular (MM) resonances. MATERIALS AND METHODS: Ten patients with KD and twelve healthy volunteers were investigated using a stimulated echo acquisition mode (STEAM) spectroscopy sequence with metabolite-nulling. RESULTS: The concentrations of Glx remained unchanged in KD. An increased myo-inositol (Ins), and elevated MM at 0.9 ppm were found within the motor area. The N-acetyl-aspartate (NAA)/creatine (Cr) ratio was negatively correlated to the number of cytosine adenosine guanine (CAG) repeats in the motor area. CONCLUSION: The elevated MM at 0.9 ppm may be attributed to a pathologically altered protein in KD. Additionally, the changes of Ins point to a clinically unexpected involvement of the motor cortex. The correlation of NAA/Cr with the number of CAG repeats indicates a link between metabolites and genetic failure.

Adult↗

PubMed2002

Proton magnetic resonance spectroscopy with metabolite nulling reveals regional differences of macromolecules in normal human brain.

PURPOSE: To quantify the macromolecular content in different anatomic brain regions and to evaluate an age dependency of the macromolecular concentrations. MATERIAL AND METHODS: A short echo time Stimulated Echo Acquisition Mode (STEAM) sequence was used without and with inversion recovery metabolite nulling in 8-12 healthy volunteers. Quantitation was achieved by an extended LCModel, and macromolecular resonances at 0.9, 1.4, 2.1, and 3.0 ppm were evaluated. RESULTS: In the cerebellum, the 1.4, 2.1, and 3.0 ppm resonances were highest compared to all other regions (P < 0.02); the 0.9 ppm resonance was significantly higher than that of pons (P < 0.01). In the motor cortex, the 0.9, 1.4, and 2.1 ppm resonances were higher than those of white matter and pons (P < 0.02). Pons and white matter did not differ significantly from each other. A significant correlation of the macromolecular concentrations with the age could not be found. CONCLUSION: There were higher macromolecular concentrations in the cerebellum and motor cortex than in pons or white matter. These were probably due to the higher portions of gray matter in these volumes of interest (VOIs) than in the other regions.

Adult↗

PubMed2002

MRI of muscular fat.

An MRI technique with high selectivity and sensitivity to the signal components in the chemical shift range of methylene and methyl protons of fatty acids has been developed for noninvasive assessment of muscular fat in vivo. A spoiled gradient-echo sequence with spatial-spectral excitation by six equidistant pulses with 2 degrees -(-9 degrees )-17 degrees -(-17 degrees )-9 degrees -(-2 degrees ) and a multi-echo train (TE = 16, 36, 56, 76, 96, and 116 ms) allowed a series of images to be recorded with a receiver bandwidth of 78 Hz per pixel. SIs from phantoms with lipid contents between 0.1% and 100% were compared to those from pure water. Thirty healthy volunteers underwent fat-selective imaging of their lower leg, and parallel localized proton spectroscopy of the tibialis anterior and the soleus muscle by a single-voxel stimulated echo acquisition mode (STEAM) technique (TR = 2 s, TE = 10 ms, TM = 15 ms). Results show a high correlation (r = 0.91) between fat imaging and the spectroscopic approach in the soleus muscle, considering the percentage total fat content of musculature. The correlation coefficient was clearly lower (r = 0.55) in the tibialis anterior muscle due to signal contaminations from adjacent subcutaneous fat in the images, inhomogeneous fat distribution, and generally lower lipid content in this muscle. Applications of the new imaging technique showed marked intra- and interindividual variability in the spatial distribution of lipids in the musculature of the lower leg. No significant correlation of the muscular fat with the thickness of the subcutaneous fat layer was found. In addition, the body mass index does not appear to determine muscular fat content, except in very obese cases.

Adult↗

PubMed2002

Metabolic characterization of a woman homozygous for the Ser113Leu missense mutation in carnitine palmitoyl transferase II.

Carnitine palmitoyl transferase (CPT) II is a key enzyme in transporting FFA into the mitochondrial matrix for beta oxidation. The clinical manifestation of CPT II deficiency is characterized mainly by myopathic symptoms. Conceivably, the inability of skeletal muscle to oxidize (long-chain) FFAs could also have far-reaching metabolic consequences, such as insulin resistance secondary to increased muscle lipids, about which relatively little is known. We therefore performed a series of metabolic studies in a 43-yr-old woman homozygous for the Ser113Leu mutation in the CPT II gene, the single most common genetic cause of CPT II deficiency, and compared the results with data from a male and female control group taken from the Tübingen family study database. The metabolic studies included oral glucose tolerance test (OGTT), euglycemic hyperinsulinemic clamp to measure insulin sensitivity, indirect calorimetry to measure substrate oxidation, stable isotopes for determination of glycerol turnover, and magnetic resonance spectroscopy for measurement of intramyocellular lipids. Compared with the female control group, the patient was normal glucose tolerant but severely insulin resistant, basal lipolysis was markedly reduced, and carbohydrate oxidation was maximally increased in the basal state and did not increase further during insulin stimulation. Conversely, lipid oxidation was virtually absent and did not decrease during insulin stimulation. Surprisingly, intramyocellular lipids were well within the range of the control group. In conclusion, genetic CPT II deficiency is characterized by insulin resistance, which is not explained by increased intramyomellular lipids. However, it may be partially explained by glucose oxidation already maximally increased in the basal state, which cannot be increased any further by insulin. Reduced basal lipolysis may represent a compensatory mechanism for the reduced oxidative FFA disposal characteristic for this disease.

Adult↗

PubMed2002

MR imaging-detected breast lesions: histopathologic correlation of lesion characteristics and signal intensity data.

OBJECTIVE: The aim of our study was to differentiate benign from malignant breast lesions that had been detected exclusively on MR imaging by analyzing qualitative and quantitative lesion characteristics. MATERIALS AND METHODS: We performed 51 MR imaging-guided breast interventions (41 preoperative lesion localizations and 10 large-core needle biopsies) in 45 patients with exclusively MR imaging-detected lesions. All patients had previously undergone diagnostic dynamic contrast-enhanced MR imaging of the breast with a double breast coil at 1.0 T (n = 36) or 1.5 T (n = 15). The diagnostic MR images were evaluated on a workstation. Lesion morphology (size, shape, margin type, enhancement pattern), signal intensity parameters (time to peak enhancement, maximum slope of enhancement curve, washout, relative water content), and scores analogous to the Breast Imaging Reporting and Data System (BI-RADS) categories were correlated with histology. RESULTS: Histology revealed malignancy in 37.3% (19/51) of the lesions. The positive predictive value for malignancy of exclusively MR imaging-detectable lesions increased as the analogous BI-RADS category increased. Late inhomogeneous contrast enhancement was the only morphologic criterion that was statistically significantly correlated with malignancy. Malignant and benign lesions did not differ significantly in any of the quantitatively evaluated signal intensity parameters. Carcinomas showed a tendency toward faster and stronger enhancement and stronger washout. CONCLUSION: The classification of exclusively MR imaging-detectable breast lesions according to a combination of morphologic and perfusion parameters including the late enhancement pattern helps identify the lesions for which interventional MR imaging is required. Quantitative signal intensity data alone do not suffice.

Adult↗