Biomedical subjects

Fritz Schick

Publications and source records attributed to Fritz Schick.

At least 19 recordsLinked to original sources

PubMed2007

Quantitative assessment of glomerular filtration rate with MR gadolinium slope clearance measurements: a phase I trial.

PURPOSE: To prospectively demonstrate the feasibility of quantifying the glomerular filtration rate (GFR) by assessing the renal clearance of gadolinium-based contrast medium from the extracellular fluid volume in healthy volunteers. MATERIALS AND METHODS: The study was approved by the ethics committee and the governmental drug administration department (registration number 4030139, EudraCT number 2004-002969-20, study protocol number 318/2004). Informed consent was obtained from 16 healthy volunteers (six female, 10 male; mean age, 24.5 years +/- 2.8 [standard deviation]). Thirteen volunteers (four women, nine men; mean age, 24.8 years +/- 2.7; range, 23-30 years) successfully contributed to the study. The GFR was assessed by recording the renal clearance of gadobutrol (3.75 mL, approximately 0.05 mmol per kilogram of body weight) at navigator-gated turbo fast low-angle shot magnetic resonance (MR) imaging. Time-signal intensity curves were constructed from manually drawn regions of interest in the liver, spleen, and renal cortex, and the GFR was calculated by using exponential fitting. Simultaneously obtained iopromide clearance measurements were the reference standard. Statistical evaluations included Bland-Altman plotting and analysis of the relative deviation from iopromide clearance. RESULTS: Evaluation of liver regions of interest revealed the lowest mean of paired differences from the iopromide clearance measurements (-5.9 mL/min per 1.73 m(2) +/- 14.6), with a mean GFR of 109.0 mL/min per 1.73 m(2) +/- 17.1 (134.1 mL/min per 1.73 m(2) +/- 35.4 for spleen, 100.7 mL/min per 1.73 m(2) +/- 25.1 for renal cortex) compared with a mean GFR of 103.1 mL/min per 1.73 m(2) +/- 9.4 measured by using iopromide clearance. The maximum deviation of MR-determined gadobutrol clearance values from iopromide clearance values was 29.2%. The mean disposition half-life of gadobutrol measured in the liver was 83.0 minutes +/- 14.2 (72.4 minutes +/- 20.2 in spleen, 92.6 minutes +/- 23.7 in renal cortex). CONCLUSION: The described MR imaging method enables absolute quantification of the GFR after routine contrast material-enhanced MR imaging.

Adult↗

PubMed2007

Optimization of blood-myocardial contrast in 3D true FISP cardiac imaging at 1.5 T.

Three-dimensional (3D) steady-state free precession (SSFP) MRI sequences are often applied to visualize both intra- and extracardiac pathologies. In the present study the contrast behavior of 3D true fast imaging with steady precession (True-FISP) sequences for cardiac imaging was optimized in numerical simulations and compared with measurements obtained in eight healthy volunteers on a 1.5 T whole-body scanner. Two SS preparation schemes in combination with and without a T(2) preparation were assessed to improve contrast between blood and myocardium using a navigator-gated and ECG-triggered 3D True-FISP sequence. Numerical simulations and experimental studies in volunteers showed that an SS preparation using a constant flip angle (CFA) is preferable to a linear flip angle (LFA) preparation in terms of contrast between blood and myocardium. The optimized 3D True-FISP sequence provides a reliable, accurate, and time-efficient means of obtaining a morphological cardiac diagnosis.

Adult↗

PubMed2006

Image-guided radiofrequency ablation of renal cell carcinoma.

The incidence of renal cell carcinoma is rising with the increased number of incidental detection of small tumours. During the past few years, percutaneous imaging-guided radiofrequency ablation has evolved as a minimally invasive treatment of small unresectable renal tumours offering reduced patient morbidity and overall health care costs. In radiofrequency ablation, thermal energy is deposited into a targeted tumour by means of a radiofrequency applicator. In recent studies, radiofrequency ablation was shown to be an effective and safe modality for local destruction of renal cell carcinoma. Radiofrequency applicator navigation can be performed via ultrasound, computed tomography or magnetic resonance guidance; however, ultrasound seems less favourable because of the absence of monitoring capabilities during ablation. On-line monitoring of treatment outcome can only be performed with magnetic resonance imaging giving the possibility of eventual applicator repositioning to ablate visible residual tumour tissue. Long-term follow-up is crucial to assess completeness of tumour ablation. New developments in ablation technology and radiological equipment will further increase the indication field for radiofrequency ablation of renal cell carcinoma. Altogether, radiofrequency ablation seems to be a promising new modality for the minimally invasive treatment of renal cell carcinoma, which was demonstrated to exhibit high short-term effectiveness.

Carcinoma, Renal Cell↗

PubMed2006

Combined passive and active shimming for in vivo MR spectroscopy at high magnetic fields.

The use of high magnetic fields increases the sensitivity and spectral dispersion in magnetic resonance spectroscopy (MRS) of brain metabolites. Practical limitations arise, however, from susceptibility-induced field distortions, which are increased at higher magnetic field strengths. Solutions to this problem include optimized shimming, provided that active, i.e., electronic, shimming can operate over a sufficient range. To meet our shim requirements, which were an order of magnitude greater than the active shim capacity of our 7T MR system, we developed a combined passive and active shim approach. Simple geometries of ferromagnetic shim elements were derived and numerically optimized to generate a complete set of second-order spherical harmonic shim functions in a modular manner. The major goals of the shim design were maximization of shim field accuracy and ease of practical implementation. The theoretically optimized ferro-shim geometries were mounted on a cylindrical surface and placed inside the magnet bore, surrounding the subject's head and the RF coil. Passive shimming generated very strong shim fields and eliminated the worst of the field distortions, after which the field was further optimized by flexible and highly accurate active shimming. Here, the passive-shimming procedure was first evaluated theoretically, then applied in phantom studies and subsequently validated for in vivo 1H MRS in the macaque visual cortex. No artifacts due to the passive shim setup were observed; adjustments were reproducible between sessions. The modularity and the reduction to two pieces per shim term in this study is an important simplification that makes the method applicable also for passive shimming within single sessions. The feasibility of very strong, flexible and high-quality shimming via a combined approach of passive and active shimming is of great practical relevance for MR imaging and spectroscopy at high field strengths where shim power is limited or where shimming of specific anatomical regions inherently requires strong shim fields.

Algorithms↗

PubMed2006

Three-dimensional morphological magnetic resonance imaging in infants and children with congenital heart disease.

BACKGROUND: Cardiac MRI has become a clinically useful supplement to ECHO and conventional X-ray angiography in the diagnostic work-up of patients with congenital heart disease (CHD). Three-dimensional (3D) sequences are capable of depicting both intracardiac and extracardiac structures with high accuracy in adults and adolescents. However, diagnostic image quality in infants and young children has not yet been reported. OBJECTIVE: To apply an optimized 3D steady-state free-precession (SSFP) MR sequence in infants and children with CHD. MATERIALS AND METHODS: In 20 patients (median age 1.8 years; ten male) with CHD, whole-chest imaging was performed with navigator-gated, isotropic 3D SSFP MRI at 1.5 T. Sequence parameters were adapted to special requirements in infancy. Measurements of intra- and extracardiac structures were performed by two independent observers and compared to spin-echo and cine gradient-recalled-echo sequences. RESULTS: Diagnostic image quality was achieved with the 3D SSFP technique in all patients, allowing the establishment of a diagnosis in all cases. Interobserver comparison of measurements from reformatted 3D SSFP datasets revealed only minor differences with standard deviations ranging from 0.3-1.3 mm for intracardiac and 0.3-0.7 mm for extracardiac anatomy (P = ns). CONCLUSION: Isotropic 3D SSFP MRI allows reliable and accurate assessment of CHD, even in free-breathing infants and young children.

Child↗

PubMed2006

Upstream transcription factor 1 gene polymorphisms are associated with high antilipolytic insulin sensitivity and show gene-gene interactions.

Upstream transcription factor 1 (USF1) regulates the expression of many genes involved in lipid and glucose metabolism, among them genes regulating lipolysis. USF1 specifically regulates the expression of the hormone-sensitive lipase gene (HSL) in adipocytes and the hepatic lipase gene (LIPC) in the liver, which was found to be involved in liver fat accumulation. The usf1s1 C > T and usf1s2 G > A single-nucleotide polymorphisms (SNPs) in USF1 are associated with increased in vitro catecholamine-induced lipolysis in adipocytes. We investigated first whether SNPs in USF1 affect the lipolysis-suppressing action of insulin in vivo, and second, whether they interact with the -60C > G SNP in HSL on lipolysis and the -514C > T SNP in LIPC on liver fat. The usf1s1 C > T and usf1s2 G > A SNPs, together with the SNPs in HSL and LIPC, were determined in 407 Caucasians. Lipolysis was estimated as a change in free fatty acid (FFA) levels from baseline to 2 h of a 75-g oral glucose tolerance test (OGTT). Fifty-four subjects had data from a euglycemic hyperinsulinemic clamp with calculation of antilipolytic insulin sensitivity. Subjects carrying the minor alleles (T of usf1s1 and A of usf1s2) had lower 2 h FFA (p = 0.01) and a larger decrease in FFA concentrations during the OGTT (p = 0.02). Antilipolytic insulin sensitivity was higher in these individuals (p = 0.03). No interaction of the usf1s1 C > T and usf1s2 G > A SNPs with the -60C > G SNP in HSL on antilipolytic insulin sensitivity was detected. Liver fat, measured by (1)H magnetic resonance spectroscopy, was elevated only in subjects who were both homozygous for the major alleles of usf1s1 and usf1s2 and carriers of the T allele of the -514C > T SNP in LIPC (p = 0.01). In conclusion, subjects carrying the T allele of SNP usf1s1 and the A allele of SNP usf1s2 have a higher antilipolytic insulin sensitivity. Moreover, both SNPs may interact with the -514C > T SNP in LIPC to determine liver fat.

Adipocytes↗

PubMed2006

The relationships of plasma adiponectin with a favorable lipid profile, decreased inflammation, and less ectopic fat accumulation depend on adiposity.

BACKGROUND: The metabolic effects of adiponectin, including insulin sensitivity, seem to become stronger with increasing adiposity. Adiposity may also affect the relationship of adiponectin concentrations with serum lipid profile; markers of inflammation, atherosclerosis, and endothelial function; and ectopic fat accumulation. METHODS: We measured plasma adiponectin concentrations, serum lipids, and serum markers of inflammation, atherosclerosis, and endothelial function in 242 Caucasians without type 2 diabetes. We also measured visceral adipose tissue with magnetic resonance tomography and liver and intramyocellular fat with (1)H magnetic resonance spectroscopy. RESULTS: We divided the study participants into 2 groups: lean [mean (SE) total body fat, 26% (0.6%); n = 119] and obese [36% (0.6%); n = 123]. In the obese group, plasma adiponectin concentrations showed a strong positive association with concentrations of HDL cholesterol (P <0.0001) and negative associations with LDL cholesterol, triglycerides, high-sensitivity C-reactive protein, interleukin 6, apolipoprotein B(100), soluble E-selectin, soluble vascular cellular adhesion molecule 1, plasminogen activator inhibitor 1, leukocyte count, and liver and intramyocellular fat (all P <0.03). In the lean group, adiponectin showed a less strong association with HDL cholesterol (P = 0.005) and liver fat (P = 0.03) and no significant associations with the other variables (all P >0.10). High visceral adipose tissue was a strong predictor of low adiponectin concentrations, particularly in the obese group, and attenuated many of the significant relationships. CONCLUSIONS: High adiponectin plasma concentrations are associated with favorable lipid profiles, decreased subclinical inflammation, decreased markers of atherosclerosis and endothelial function, and low ectopic fat accumulation, particularly in obese persons. Adiponectin may also have a concentration-related effect on the relationship between visceral adipose tissue and these metabolic characteristics, especially in obese persons.

Adiponectin↗

PubMed2006

Solitary pulmonary nodules: association between signal characteristics in dynamic contrast enhanced MRI and tumor angiogenesis.

PURPOSE: To estimate the association between signal characteristic of dynamic enhanced MRI using curve types and angiogenesis in solitary pulmonary nodules. MATERIALS AND METHODS: Thirty-six patients with a solitary pulmonary nodule (SPN) ranging in size from 6 to 37 mm (median 17 mm) underwent dynamic contrast enhanced MRI with a time interval of 10 s over a total period of 4 min. Resulting from the time-intensity curves four different enhancement curve profiles (A-D) were defined: type A with strong increase followed by early washout, type B with strong increase without washout, type C with slow increase and type D without relevant increase. Maximum peak (Pmax), slope of the first bolus transit (slope) and washout were calculated. Microvessel densities (MVD) were counted at the margins and at the center of the nodules. The mean MVD of each nodule was calculated. Enhancement characteristics were correlated with MVD grouped by diagnosis and by curve types. Curve types were correlated with the score of vascular endothelial growth factor (VEGF). RESULTS: The frequency of malignancy was 55% (20/36). Using curve types for differentiation between malignant and benign SPN, the sensitivity, specificity and accuracy were 100%, 75% and 89%, respectively. The correlation between Pmax and MVD(mean) for all nodules was moderate (r(s)=0.4, P=0.02). A relevant correlation was found between Pmax and MVD(margin) in curve type A (r(s)=0.63; P=0.04) and Pmax and MVD(mean) in curve type C (r(s)=0.86; P=0.006). No positive correlation was found between Pmax and MVD (mean, center and margin) in curve type B. No significant correlation was found for slope and washout. VEGF score correlated positively with curve types (r(s)=0.67; P<0.001). CONCLUSION: A relevant association between perfusion curve profiles and angiogenesis was found in malignant nodules having early washout and in benign lesion with a slow increase of enhancement. In cases of strong signal increase without washout additional factors for enhancement must be considered. The use of curve profiles could allow for the estimation of the extent of VEGF.

Adenocarcinoma↗

PubMed2006

Numerical simulations of intra-voxel dephasing effects and signal voids in gradient echo MR imaging using different sub-grid sizes.

Signal void artifacts in gradient echo imaging are caused by the intra-voxel dephasing of the spins. Intra-voxel dephasing can be estimated by computing the field distribution on a sub-grid inside each picture element, followed by integration of all magnetization components. The strategy of computing the artifacts based on the integration of the sub-voxel signal components is presented here for different sub-grids. The coarseness of the sub-grid is directly related to computational effort. The possibility to save memory space and computing time for the dipole model by computing the field only on a sub-grid is addressed in the presented article. It is investigated as to how far computational time and memory space can be reduced by using an appropriate sub-grid. Numerical results for a model of a partially diamagnetically coated needle shaft are compared to experimental findings. In the case of a pure titanium needle, it is shown as being sufficient to compute the field distribution on a sub-grid that is at least four times coarser in each direction than the grid used to discretize the object in the related MR image. Due to three nested loops over the 3D grid, the need for memory space and time is saved by a factor 64. Deviations between measurements and simulations for the broad side of the artifact (uncompensated) and for the small side of the artifact (compensated) were 15.5%, respectively, 19.1% for orientation parallel to the exterior field, and 22.7%, respectively, 23.1% for orientation perpendicular to the exterior field.

Artifacts↗

PubMed2006

Contrast-enhanced dynamic MR nephrography using the TurboFLASH navigator-gating technique in children.

The purpose of this work was to test the feasibility of an MR examination protocol for the comprehensive assessment of renal morphology, excretion and split renal function using a navigator-gated TurboFLASH sequence. A navigator-gated T1-weighted single-slice TurboFLASH sequence suitable for dynamic MR urography and nephrography was implemented. A protocol was developed allowing for assessment of urinary excretion and split renal function by recording the renal clearance of a gadolinium (Gd) diethylene-triamine-pentacetic-acid (DTPA) bolus. Ten patients aged between 14 months and 14 years (mean age 4.8+/-4.6 years) were evaluated with the following indications: pelvicalyceal dilatation (n=4), follow-up after pyeloplasty (n=1), duplex systems (n=3), large renal cyst (n=1), and renal insufficiency (n=1). Dynamic MR urography and MR split renal function were compared to MAG3 scintigraphy. Evaluation of morphology, excretion and function required 50-60 minutes examination time, plus 10 minutes for post-processing. The TurboFLASH sequence yielded image acquisition at nearly identical diaphragm positions allowing for accurate region-of-interest evaluation within the renal parenchyma and the urinary passage. Static and dynamic MR urography showed the morphology of the urinary tract and excretion with sufficient diagnostic imaging quality, and the results were in diagnostic compliance with scintigraphy. MRI and scintigraphy yielded similar results for split renal function with a correlation coefficient of R=0.968 determined by linear regression. Our conclusions were that the method is robust, easy to perform on a clinical 1.5 T MRI system, rapid to evaluate and post-process and, therefore, easy to incorporate into clinical routine. Compared to scintigraphy, the higher spatial resolution of the MR examination provides additional important information improving the management of the pediatric patients without the application of radioactive tracers.

Adolescent↗

PubMed2006

Morphological, contrast-enhanced and spin labeling perfusion imaging for monitoring of relapse after RF ablation of renal cell carcinomas.

MR perfusion imaging was applied for the assessment of completeness in the destruction of renal cell carcinomas by RF ablation (RFA) in a pilot study. An arterial spin labeling (ASL) approach was compared to conventional contrast-enhanced T1-weighted (CE-T1w) imaging. Ten patients suffering from renal cell carcinoma were treated by RFA. For the assessment of the extent of coagulation and for the detection of residual tumor, T1-weighted gradient-echo imaging, T2-weighted spin echo imaging and two different perfusion imaging techniques were performed before, 1 day and 6 weeks after RFA at 1.5 T. Perfusion imaging comprised CE-T1 weighted and FAIR-TrueFISP ASL imaging. Perfusion images recorded in the acute stage after RFA showed higher compliance to the definitive ablation volume reached after 6 weeks than T2-weighted images, which underestimated the true necrosis size. In the detection of residual tumor tissue, both modalities complimented each other. The exclusion of residual tumor tissue could more reliably be performed using perfusion-imaging methods. Both perfusion-imaging modalities showed sufficient imaging quality for post-interventional monitoring. Perfusion imaging provides a higher predictability of the completeness of tumor ablation and extent of coagulation than T2-weighted imaging alone. Since the results of the FAIR-TrueFISP sequence are promising, the administration of potentially nephrotoxic contrast media may be avoided in the respective patient cohort.

Aged↗

PubMed2006

Perfusion MR imaging with FAIR true FISP spin labeling in patients with and without renal artery stenosis: initial experience.

The purpose of this study was to prospectively evaluate an arterial spin-labeling technique, flow-sensitive alternating inversion-recovery (FAIR) true fast imaging with steady-state precession (FISP), for noninvasive quantification of renal perfusion in patients without a history of renal artery stenosis (RAS) and in patients with proved RAS. The study was approved by the local ethics committee, and all participants provided written informed consent. Six patients with hypertension but no history of renal artery disease and 12 patients with RAS underwent FAIR true FISP magnetic resonance (MR) imaging in a whole-body 1.5-T unit. RAS grade and scintigraphic perfusion data served as the reference standards. On the FAIR true FISP perfusion images, severe RAS (>70% luminal narrowing) could be clearly distinguished from no or mild RAS and moderate RAS (< or =70% luminal narrowing) (P < .005). Significant correlations between FAIR perfusion data and stenosis grade (r = -0.76) and between FAIR and single photon emission computed tomographic perfusion values (r = 0.83) were observed. FAIR true FISP was found to be suitable for quantitative perfusion imaging of the kidneys in patients with RAS.

Aged↗

PubMed2006

New imaging techniques of fat, muscle and liver within the context of determining insulin sensitivity.

Body fat distribution and ectopic fat deposition are important determinants of insulin sensitivity. Fat deposition in muscle and the liver, in particular, has been found to impair insulin signalling in these insulin-sensitive tissues. Thus, exact quantification of fat content may help to distinguish between different sites of insulin resistance. Increased fat deposition in the visceral compartment compared with the subcutaneous depot also represents an important factor leading to insulin resistance. Recent data clearly showed that visceral fat is a strong determinant of liver fat content. Exact quantification of fat distribution by magnetic resonance imaging and magnetic resonance spectroscopy may help to define distinct 'fat-distribution phenotypes'. This may allow a search for new candidate genes for type 2 diabetes mellitus and identify, at an early stage, individuals at risk for decline in insulin sensitivity.

Body Fat Distribution↗

PubMed2006

Eddy-current induction in extended metallic parts as a source of considerable torsional moment.

PURPOSE: To examine eddy-current-provoked torque on conductive parts due to current induction from movement through the fringe field of the MR scanner and from gradient switching. MATERIALS AND METHODS: For both cases, torque was calculated for frames of copper, aluminum, and titanium, inclined to 45 degrees to B0 (maximum torque case). Conditions were analyzed in which torque from gravity (legal limit, ASTM F2213-02) was exceeded. Experiments were carried out on a 1.5 T and a 3 T scanner for copper and titanium frames and plates (approximately 50 x 50 mm2). Movement-induced torque was measured at patient table velocity (20 cm/second). Alternating torque from gradient switching was investigated by holding the specimens in different locations in the scanner while executing sequences that exploited the gradient capabilities (40 mT/m). RESULTS: The calculations predicted that movement-induced torque could exceed torque from gravity (depending on the part size, electric resistance, and velocity). Two experiments on moving conductive frames in the fringe fields of the scanners confirmed the calculations. For maximum torque case parameters, gradient-switching-induced torque was calculated to be nearly 100 times greater than the movement-induced torque. Well-conducting metal parts located off center vibrated significantly due to impulse-like fast alternating torque characteristics. CONCLUSION: Torque on metal parts from movement in the fringe field is weak under standard conditions, but for larger parts the acceptable limit can be reached with a high static field and increased velocity. Vibrations due to gradient switching were confirmed and may explain the sensations occasionally reported by patients with implants.

Aluminum↗

PubMed2006

Whole-body magnetization transfer contrast imaging.

PURPOSE: To demonstrate the feasibility of whole-body magnetization transfer (MT) contrast imaging. MATERIALS AND METHODS: Whole-body MT imaging was performed on eight healthy volunteers and five patients (mean age=40.5+/-17.8 years) with diagnoses of dermatomyositis (N=1), B-symptoms with suspicion of paraneoplastic disease (N=1), metastatic malignant melanoma (N=1), and multiple sclerosis (MS) (N=2). Measurements were carried out on a 1.5-Tesla whole-body MR scanner capable of parallel signal reception. A three-dimensional (3D) gradient-echo sequence (TR=17 msec, TE=4.8 msec, flip angle=10 degrees) was applied in combination with a Gaussian off-resonance MT preparation pulse acting at an off-resonance of 1.500 Hz with a 500 degrees effective flip angle. Whole-body images were constructed from five different body regions. RESULTS: In all subjects, whole-body MT contrast images were obtained within less than 20 minutes of measuring time. The images showed sufficient diagnostic image quality to assess the patients' pathologies. The MT ratios (MTRs, in percent units) for the volunteers were as follows: white matter (WM) 51.1+/-1.0, gray matter (GM) 42.2+/-1.3, skeletal muscle (mean value of four muscle groups) 50.3+/-2.1, liver 39.4+/-3.2, spleen 31.8+/-2.6, renal cortex 30.4+/-1.9, and renal medulla 25.6+/-1.3. The MTRs for the pathologies were as follows: skeletal muscle in dermatomyositis approximately 30, metastases in malignant melanoma 30.7-36.0, uterus myoma 49.3, and MS lesions 30-40. CONCLUSION: Our preliminary data indicate that MT contrast in whole-body MRI is feasible, and may be useful for rapid whole-body assessment of diseases that exhibit high contrast in MT imaging, such as MS and muscular disorders.

Adult↗

PubMed2006

Hepatic lipid accumulation in healthy subjects: a comparative study using spectral fat-selective MRI and volume-localized 1H-MR spectroscopy.

Fat-selective MRI was applied to assess the amount and spatial distribution of hepatic lipids (HL) in healthy subjects. The results were compared with those obtained by localized 1H-MR spectroscopy (MRS). Ninety subjects (23-63 years old) underwent single-slice fat-selective MRI with spatial-spectral excitation and volume-localized spectroscopy at 1.5 T. HLs were analyzed in ventral and dorsal regions of interest (ROIs) of the liver in fat-selective images. Spectra were evaluated using the integral signal of methylene and methyl signals. The fat-selective images showed smooth and homogeneous distribution of HL over the entire cross section of the liver. There was, however, a marked interindividual variability in the amount of HL. MRS revealed a lipid signal fraction between 0.5% and 39.3%. The fat content in the ROIs in images correlated well with the spectroscopic results (r >or= 0.95). Both techniques provide sufficient sensitivity for a reliable and quantitative assessment of liver steatosis in subjects without liver disease. 1H-MRS has a higher sensitivity compared to MRI, especially for small amounts of HL, which may be of interest for metabolic interventions. Fat-selective images provide more spatial information about fat distribution, which makes this technique suitable for clinical imaging of patients with liver disease.

Adult↗

PubMed2006

Quantitative lung perfusion mapping at 0.2 T using FAIR True-FISP MRI.

Perfusion measurements in lung tissue using arterial spin labeling (ASL) techniques are hampered by strong microscopic field gradients induced by susceptibility differences between the alveolar air and the lung parenchyma. A true fast imaging with steady precession (True-FISP) sequence was adapted for applications in flow-sensitive alternating inversion recovery (FAIR) lung perfusion imaging at 0.2 Tesla and 1.5 Tesla. Conditions of microscopic static field distribution were assessed in four healthy volunteers at both field strengths using multiecho gradient-echo sequences. The full width at half maximum (FWHM) values of the frequency distribution for 180-277 Hz at 1.5 Tesla were more than threefold higher compared to 39-109 Hz at 0.2 Tesla. The influence of microscopic field inhomogeneities on the True-FISP signal yield was simulated numerically. Conditions allowed for the development of a FAIR True-FISP sequence for lung perfusion measurement at 0.2 Tesla, whereas at 1.5 Tesla microscopic field inhomogeneities appeared too distinct. Perfusion measurements of lung tissue were performed on eight healthy volunteers and two patients at 0.2 Tesla using the optimized FAIR True-FISP sequence. The average perfusion rates in peripheral lung regions in transverse, sagittal, and coronal slices of the left/right lung were 418/400, 398/416, and 370/368 ml/100 g/min, respectively. This work suggests that FAIR True-FISP sequences can be considered appropriate for noninvasive lung perfusion examinations at low field strength.

Adolescent↗

PubMed2006

Quantitative ASL muscle perfusion imaging using a FAIR-TrueFISP technique at 3.0 T.

The feasibility of muscle perfusion imaging with diagnostic image quality was demonstrated using the FAIR-TrueFISP arterial spin labeling technique on a clinical 3.0 T whole-body scanner. In eight healthy volunteers (24 to 42 years old), quantitative perfusion maps of the forearm musculature were acquired before and after intense exercise. All measurements were carried out in a 3.0 T whole-body MR unit in combination with an eight-channel head coil. Pulsed arterial spin labeling and data recording were performed with an adapted FAIR-TrueFISP technique and quantitative perfusion maps were calculated on a pixel-by-pixel basis by means of the extended Bloch equations. Perfusion images with an in-plane resolution of 1 mm showed no significant distortions or blurring. Perfusion-time curves could be recorded with a temporal resolution of 6.4 s. Maximum perfusion in the musculature was found approximately 2 min after exercise, reaching values of up to 220 mL/min per 100 g of tissue with good delineation between the active muscles and the musculature not involved in the exercise. In conclusion, the TrueFISP pulsed arterial spin labeling technique allows patient-friendly assessment of muscular perfusion in a clinical whole-body scanner.

Adult↗