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| | | | | | | Searchterm 'HIS' was also found in the following services: | | | | |
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(Mn-DPDP) T his agent, mangafodipir trisodium, is a hepatocyte specific MRI contrast agent. Manganese is very toxic, so it has to be chelated and put in the form of a vitamin B6 analog, which is taken up by normal hepatocytes to some extent.
Teslascan® was developed in the early 1980's, went through clinical trials in the early 1990's, and was approved in 1997. One problem with assessing the efficacy of t his agent is the fact that the phase III trials finished in the early 1990's, and the techniques used for MR today are very different from the techniques used almost a decade ago.
T his contrast agent shortens the T1 relaxation time. On T1 weighted pictures it makes a normal liver look brighter. Since metastases, for example, do not generally take up t his agent, the contrast between the enhancing liver and the non-enhancing lesions will increase on T1 weighted pictures. It does not have much effect on T2 weighted images.
Drug Information and Specification T1, Predominantly positive enhancement PHARMACOKINETIC Hepatobiliary, pancreatic, adrenal DOSAGE 5 µmol/kg, 0.5 ml/kg PREPARATION Finished product DEVELOPMENT STAGE Approved PRESENTATION Vials of 100 ml DO NOT RELY ON THE INFORMATION PROVIDED HERE, THEY ARE NOT A SUBSTITUTE FOR THE ACCOMPANYING PACKAGE INSERT!
Distribution Information TERRITORY TRADE NAME DEVELOPMENT STAGE DISTRIBUTOR | | | | | Further Reading: | | Basics:
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Quick Overview
Please note that there are different common names for t his artifact.
DESCRIPTION
Edge ringing, syrinx-like stripe
A data truncation artifact may occur when the interface between high and low signal intensities is encountered in one imaging plane. The 2D-FT techniques transform the MR signal to spatial intensity image data with frequency and phase information encoding each axis in the plane of the scan. T his artifact is found in both frequency and phase axes.
Artifactual ripples adjacent to edges in an image or sharp features in a spectrum, caused by omission of higher frequency terms in Fourier transformation, particularly with the use of zero filling to replace unsampled higher frequencies.
Complex shapes are specified by series of sine and cosine waves of various frequencies, phase and amplitude. Some shapes are more difficult to encode than others. The most difficult shapes to represent with Fourier series of terms are waveforms with instantaneous transitions, tissue discontinuities or edges. The low-frequency components of the series describe the overall shape of the step function. Higher frequency components are needed to describe the corners if the step function more accurately.
If not enough samples are taken, these areas cannot be accurately represented.
The truncation of the infinite data series results in a ringing artifact because of the inability to accurately approximate t his tissue discontinuity with a shorter truncated data set. Therefore, the ringing that occurs at all tissue boundaries on MR is called truncation artifact.
Image Guidance
| | | | • View the DATABASE results for 'Truncation Artifact' (2).
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A technique, which produces a 3 dimensional image of an object. The advantage of t his approach is that the signal, acquired from the entire volume has an increased SNR. 'Slices' are defined by a second phase encoded axis, which divides the volume into 'partitions'.
There is no gap between the slices in 3D volume imaging, therefore thin slices are possible. The Gz phase encoding gradient is set for several slices in one. But 3D takes more time with thin slices because of t his phase encoding gradient. With conventional thin slice imaging, the SNR is poor, with 3D volume imaging t his is not the case because the slab (volume) is responsible for SNR. | | | | | | • View the DATABASE results for '3 Dimensional Imaging' (5).
| | | • View the NEWS results for '3 Dimensional Imaging' (1).
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Quick Overview Please note that there are different common names for t his artifact.
DESCRIPTION
Black contours at boundaries
Image Guidance
| | | | • View the DATABASE results for 'Black Boundary Artifact' (4).
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Contrast enhanced GRE sequences provide T2 contrast but have a relatively poor SNR. Repetitive RF pulses with small flip angles together with appropriate gradient profiles lead to the superposition of two resonance signals.
The first signal is due to the free induction decay FID observed after the first and all ensuing RF excitations.
The second is a resonance signal obtained as a result of a spin echo generated by the second and all addicted RF-pulses.
Hence it is absent after the first excitation, it is a result of the free induction decay of the second to last RF-excitation and has a TE, which is almost 2TR.
For t his echo to occur the gradients have to be completely symmetrical relative to the half time between two RF-pulses, a condition that makes it difficult to integrate t his pulse sequence into a multiple slice imaging technique.
The second signal not only contains echo contributions from free induction decay, but obviously weakened by T2-decay.
Since the echo is generated by a RF-pulse, it is truly T2 rather than T2* weighted. Correspondingly it is also less sensitive to susceptibility changes and field inhomogeneities.
Companies use different acronyms to describe certain techniques.
Different terms (see also acronyms) for these gradient echo pulse sequences:
CE-FAST Contrast Enhanced Fourier Acquired Steady State,
CE-FFE Contrast Enhanced Fast Field Echo,
CE-GRE Contrast Enhanced Gradient-Echo,
DE-FGR Driven Equilibrium FGR,
FADE FASE Acquisition Double Echo,
PSIF Reverse Fast Imaging with Steady State Precession,
SSFP Steady State Free Precession,
T2 FFE Contrast Enhanced Fast Field Echo (T2 weighted).
In t his context, 'contrast enhanced' refers to the pulse sequence, it does not mean enhancement with a contrast agent. | | | | • View the DATABASE results for 'Contrast Enhanced Gradient Echo Sequence' (4).
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