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M K Stehling

Publications and source records attributed to M K Stehling.

At least 37 records · Page 2Linked to original sources
PubMed1995

[Possibilities of technical and methodological optimization of functional magnetic resonance tomography].

The techniques of in vivo functional magnetic resonance imaging (fMRI) have been established over the past few years. Signal changes resulting from small differences in the magnetic resonance signal caused by variations in the oxygenation state of the venous vasculature are used to map neuronal activity of the brain. While many of the advantages for using MRI for functional neuroimaging are quite obvious (high spatial and temporal resolution, direct anatomic correlation, noninvasiveness), the underlying mechanisms and problems are not fully known. This article focuses on selected topics of fMRI techniques and their problems, such as field strength B0, different types of sequences and their parameters, 2D and 3D data acquisition, different statistical methods and motion artifacts. The authors favor the use of a 1.5 T clinical scanner with EPI capabilities, 2D FLASH sequences with a TR < 60 ms, TE = 30-40 ms, alpha < 20 degrees for high resolution and sensitivity, fMRI and multislice EPI for high temporal and overview and fMRI as well as cross-correlation for post-processing.

Arousal↗
PubMed1995

[Functional magnetic resonance tomography of the basal ganglia. Use of FLASH sequences for mapping activity with BOLD contrast ane high resolution].

The activation pattern of putamen, internal and external division of globus pallidus was investigated during rapid pronation and supination of the right and left hand in 12 normal volunteers using a FLASH sequence with high resolution for functional magnetic resonance imaging (fMRI) at 1.5 T. The chosen paradigm for motor function led to a signal increase within the basal ganglia between 3 and 23%, depending on the structure and individual subject. In all cases significant activation could be found contralateral to the moving hand. In six cases activation was also found on the ipsilateral side. The activated areas within putamen, internal and external division of globus pallidus were less than 5 mm2. These first results indicate that fMRI studies of basal ganglia are feasible and might be suitable for analyzing basal ganglia disorders.

Adult↗
PubMed1995

[Fast and ultra-fast magnetic resonance tomography. Basic principles, pulse sequences and special properties].

The aim of this article is the systematic treatment of fast and ultrafast magnetic resonance imaging (MRI) techniques. Based on the basic principles of signal generation and spatial encoding with magnetic field gradients the differences and important similarities of pulse sequences will be explained. We suggest to replace the conventional grouping of pulse sequences in gradient and spin-echo sequences through single and multi-echo sequences, since the latter is more precise and helpful. We illustrate how single-echo sequences such as "spin-echo", FLASH, FISP, PSIF, CISS and DESS can be derived from a single gradient echo and how multi-echo sequences such as turbo spin-echo RARE, HASTE and GRASE are based on echo-planar imaging. The different properties, advantages and disadvantages of the various sequences will be discussed and frequently used acronyms will be explained.

Echo-Planar Imaging↗
PubMed1995

[Use of ultra-fast computerized tomography in diagnosis of coronary heart disease].

Ultrafast or electron beam tomography (EBT) permits acquisition of images in 50-100 ms. An artifact-reduced display of heart and vessel structures as well as calcifications can be achieved. Therefore, EBT can be used for the detection and quantification of coronary artery calcification. Thirty-two patients with known coronary artery disease (CAD) were studied by EBT with and without i.v. contrast enhancement and with conventional coronary angiography. Different scoring systems were applied in order to define the basis to compare the data. The results showed a high EBT sensitivity for detection of coronary artery stenosis of up to 94% but low specificity with a maximum of 75%, depending on the scoring system applied. With EBT, differentiation between significant CAD (> 75%) and low-grade CAD (0-75%) showed significant results. The scoring system is not yet completely satisfactory, and with the integration of other screening tests and continuous development of scoring systems, the significance and reliability of this method in evaluation of CAD are expected to increase.

Aged↗
PubMed1994

CT angiography: expanded clinical applications.

In this essay, the potential of vascular imaging with helical CT is explored. The speed and ease with which volumes of interest can be depicted with high resolution and the ability of CT to resolve small differences in electron density allow imaging of vascular territories with IV injection of iodinated contrast materials. Vascular and combined vascular/soft-tissue/bone imaging make CT a powerful clinical tool. The technique is predominantly used for evaluation of atherosclerotic disease of the carotid bifurcation, the renal arteries, and the major abdominal vessels. A variety of display options, such as surface rendering and maximum intensity projection (MIP), have different advantages and are often complementary. The time taken to produce clinically acceptable images has been markedly reduced to between 15 and 30 min. Some of the limitations are related to the length of vascular coverage, the contrast load, and the need for exact timing. On the other hand, the technique is not affected by flow artifacts. CT angiography is now a reliable and practical clinical test that may be a useful adjunct to conventional CT.

Angiography↗
PubMed1994

[MRI of the coronary arteries: possibilities and limits. A comparative presentation with reference to coronary angiography, echocardiography and electron beam tomography].

The depiction of coronary arteries with magnetic resonance angiography has become possible during the last few years. Powerful magnetic field gradients with short ramp times and improved RF components and pulse sequences, such as derivatives of FLASH and echoplanar imaging, have led to high expectations. Because spatial resolution is still restricted and the signal-to-noise ratio (SNR) limited as it cannot be increased easily, and because the data acquisition times are relatively long compared to the respiratory and cardiac cycle, the diagnostic value currently appears to be limited. Electron beam tomography constitutes an alternative to MRI. This computer tomographic method affords acquisition times of 50-100 ms with good SNR and high spatial resolution through deflection of an electron beam onto a ring anode and by using a stationary detector. Together with transoesphageal ultrasound, these non-invasive alternative methods for the depiction of coronary arteries are compared with the "gold standard" of conventional coronary angiography, and an overview of current results is given.

Coronary Angiography↗
PubMed1993

Prolonged monitoring of the upper gastrointestinal tract using echo planar magnetic resonance imaging.

Upper gastrointestinal motility and transit has been studied in five human volunteers with the ultra high speed, magnetic resonance imaging (MRI) technique MBEST (Modulus Blipped Echo-planar Single pulse Technique), a variant of echo planar imaging. Snapshot images requiring a data acquisition time of only 64-128 msec allowed visualisation of peristalsis in the antrum and duodenum in real time, without motional image degradation, as would normally be seen using conventional MRI. Gastroduodenal flow of the luminal contents was visualised using water as a contrast medium, with appropriate adjustment of the time constant (T2) weighting of the system. Rapid (0.3 Hz) imaging of gastroduodenal motility in both transverse and coronal planes was achieved by respiratory gating to the imaging frequency, allowing repetition rates of up to 20 frames per minute for 2-3 hours. Fast replay of stored images, to produce a 'movie loop', allowed identification of fasting motility patterns of the gastric antrum and proximal small intestine, with depiction of the phases of the migrating motor complex. Images of the fed patterns after the ingestion of a test meal showed good separation of solid and liquid particulate matter and mixing waves in the gastric body. The potential for quantitative measurements with this new imaging modality of the gastrointestinal tract is under development, which will allow us to measure transit and correlate this with motility data.

Adult↗
PubMed1993

[Radiologic and ultrasound detection of gallstones].

Ultrasonography (US) is the method of choice for evaluation of gallbladder stones with an accuracy of 96%. Number, size and calcification can be assessed by virtue of US reflection and attenuation. If more than five stones are present, the accuracy decreases. To determine the calcium content of stones more precisely, computed tomography can be used. This allows an assessment of the success rate of lithotripsy and chemolysis. Oral cholecystography is an alternative method of similar accuracy as US. It provides additional information about the patency of the cystic duct. In the presence of ductal stones, the accuracy of US decreases to 30%, mainly because of overlying bowel gas. Since 8 to 16% of all cases of cholecystolithiasis are accompanied by choledocholithiasis and since this entails a change in treatment, intravenous cholecystocholangiography with an accuracy of more than 90% is the method of choice in this case. Additionally, it provides knowledge on the biliary anatomy preoperatively. It does not, however, replace US, because opacification of the gallbladder is limited with this method. If intravenous cholecystocholangiography fails in case of impaired liver function, transcholecystic cholangiography or, in cases of dilated ducts, percutaneous transhepatic cholangiography can be used. Plain film radiography is not a suitable technique, since only 10 to 15% of all gallstones calcify.

Calcinosis↗
PubMed1991

Echo-planar imaging: magnetic resonance imaging in a fraction of a second.

Progress has recently been made in implementing magnetic resonance imaging (MRI) techniques that can be used to obtain images in a fraction of a second rather than in minutes. Echo-planar imaging (EPI) uses only one nuclear spin excitation per image and lends itself to a variety of critical medical and scientific applications. Among these are evaluation of cardiac function in real time, mapping of water diffusion and temperature in tissue, mapping of organ blood pool and perfusion, functional imaging of the central nervous system, depiction of blood and cerebrospinal fluid flow dynamics, and movie imaging of the mobile fetus in utero. Through shortened patient examination times, higher patient throughput, and lower cost per MRI examination, EPI may become a powerful tool for early diagnosis of some common and potentially treatable diseases such as ischemic heart disease, stroke, and cancer.

Diffusion↗
PubMed1991

Observation of cerebrospinal fluid flow with echo-planar magnetic resonance imaging.

Using echo-planar (EP) magnetic resonance imaging (MRI), cerebrospinal fluid (CSF) flow patterns have been demonstrated in the normal subject and patients with pathological conditions including communicating hydrocephalus, aqueduct stenosis and syringohydromyelia. Snap-shot imaging times of 128 ms allow detailed demonstration of transient intraventricular CSF flow patterns, which is not possible with conventional MRI. The potential of EPI as a method for qualitative and quantitative assessment of CSF dynamics is illustrated.

Cerebral Aqueduct↗
PubMed1990

Echo-planar imaging of the human fetus in utero.

We have demonstrated that echo-planar imaging can be used to produce high-quality snapshot images of the human fetus in utero in a fraction of a second. These images are free of motional artifact or blurring and allow detailed depiction of fetal structures in normal and pathological pregnancies.

Fetal Heart↗
PubMed1990

Inversion-recovery echo-planar imaging (IR-EPI) at 0.5 T.

Echo-planar imaging is used in combination with a spin preparation phase to produce a T1-weighted image. The small additional time penalty in this procedure does not detract significantly from the ultrahigh-speed imaging capability of EPI, allowing a rapid real-time optimization of tissue parameters in the image display. Results obtained on a head demonstrate this technique.

Electron Spin Resonance Spectroscopy↗
PubMed1990

High-speed multislice T1 mapping using inversion-recovery echo-planar imaging.

Tissue contrast in MR images is a strong function of spin-lattice (T1) and spin-spin (T2) relaxation times. However, the T1 relaxation time is rarely quantified because of the long scan time required to produce an accurate T1 map of the subject. In a standard 2D FT technique, this procedure may take up to 30 min. Modifications of the echo-planar imaging (EPI) technique which incorporate the principle of inversion recovery (IR) enable multislice T1 maps to be produced in total scan times varying from a few seconds up to a minute. Using IR-EPI, rapid quantification of T1 values may thus lead to better discrimination between tissue types in an acceptable scan time.

Fourier Analysis↗
PubMed1990

Study of internal structure of the human fetus in utero by echo-planar magnetic resonance imaging.

The ultrafast echo-planar magnetic resonance imaging technology, developed and built in Nottingham, has been used to produce the first snapshot images of the human fetus in utero. The imager, operating at a proton resonance frequency of 22 MHz, produces transaxial views in 64 or 128 milliseconds. These images comprise either 64 x 128 or 128 x 128 pixels with an in-plane resolution of 3 x 3 mm2. The slice thickness is 10 mm. Fetal scans of up to 32 contiguous slices are produced in a few minutes. These have been used to study the internal structure of the uterus and the fetus in a range of cases with gestations ranging from 26 weeks to term. Echo-planar imaging seems particularly suitable as an imaging modality since its high speed obviates image blurring arising from fetal motion.

Fetal Diseases↗