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This family of sequences uses a balanced gradient waveform. This waveform will act on any stationary spin on resonance between 2 consecutive RF pulses and return it to the same phase it had before the gradients were applied.
A balanced sequence starts out with a RF pulse of 90° or less and the spins in the steady state. Prior to the next TR in the slice encoding, the phase encoding and the frequency encoding direction, gradients are balanced so their net value is zero. Now the spins are prepared to accept the next RF pulse, and their corresponding signal can become part of the new transverse magnetization. If the balanced gradients maintain the longitudinal and transverse magnetization, the result is that both T1 and T2 contrast
are represented in the image.
This pulse sequence produces images with increased signal from fluid (like T2 weighted sequences), along with retaining T1 weighted tissue contrast. Balanced sequences are particularly useful in cardiac MRI. Because this form of sequence is extremely dependent on field homogeneity, it is essential to run a shimming prior the acquisition.
Usually the gray and white matter contrast is poor, making this type of sequence unsuited for brain MRI. Modifications like ramping up and down the flip angles can increase signal to noise ratio and contrast of brain tissues (suggested under the name COSMIC - Coherent Oscillatory State acquisition for the Manipulation of Image Contrast).
These sequences include e.g. Balanced Fast Field Echo (bFFE), Balanced Turbo Field Echo ( bTFE), Fast Imaging with Steady Precession ( TrueFISP, sometimes short TRUFI), Completely Balanced Steady State (CBASS) and Balanced SARGE (BASG). | | | | | | • View the DATABASE results for 'Balanced Sequence' (5).
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FDA cleared and CE Mark 2011.
The Biograph mMR has a fully-integrated design for simultaneous PET/MRI imaging. The dedicated hardware includes solid-state, avalanche photodiode PET detector and adapted, PET-compatible MR coils.
The possibility of truly simultaneous operation allows the acquisition of several magnetic resonance imaging ( MRI) sequences during the positron emission tomography (PET) scan, without increasing the examination time.
See also Hybrid Imaging.
Device Information and Specification
CLINICAL APPLICATION
Whole Body
CONFIGURATION
Simultaneous PET/MRI
26 cm (typical overlap 23%)
A-P 45, R-L 50, H-F 50 cm
PET RING DIAMETER
65.6 cm
PATIENT SCAN RANGE
199 cm
HORIZONTAL SPEED
200 mmsec
PET DETECTOR
Solid state, 4032 avalanche photo diodes
DETECTOR SCINTILLATION MATERIAL
LSO, 28672 crystals
CRYSTAL SIZE
4 x 4 x 20 mm
DIMENSION H*W*D (gantry included)
335 x 230 x 242 cm (finshed covers)
COOLING SYSTEM
PET system: water; MRI system: water
Aautomatic, patient specific shim; active shim 3 linear and 5 non-linear channels (seond order)
POWER REQUIREMENTS
380 / 400 / 420 / 440 / 460 / 480 V, 3-phase + ground; Total system 110kW
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Device Information and Specification
CLINICAL APPLICATION
Dedicated extremity
SE, GE, IR, STIR, FSE, 3D CE, GE-STIR, 3D GE, ME, TME, HSE
IMAGING MODES
Single, multislice, volume study, fast scan, multi slab
2D: 2 mm - 10 mm;
3D: 0.6 mm - 10 mm
4,096 gray lvls, 256 lvls in 3D
POWER REQUIREMENTS
100/110/200/220/230/240
| | | | • View the DATABASE results for 'C-SCAN™' (4).
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