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Contrast to Noise Ratio
 
(CNR) In Magnetic Resonance Imaging MRI, Contrast to noise ratio is the relationship of signal intensity differences between two regions, scaled to image noise. Improving CNR increases perception of the distinct differences between two clinical areas of interest. A contrast to noise ratio is a summary of SNR and contrast. It is the difference in SNR between two relevant tissue types.
(A and B): CNR = SNRA - SNRB

See also Signal Intensity, Signal to Noise Ratio and Medical Imaging.
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• Related Searches:
    • Contrast Reversal
    • Noise
    • Image Quality
    • Contrast Resolution
    • Image Contrast Characteristics
 
Further Reading:
  Basics:
Vascular Filters of Functional MRI: Spatial Localization Using BOLD and CBV Contrast
Contrast mechanisms in magnetic resonance imaging
2004   by www.iop.org    
Optimal k-Space Sampling for Dynamic Contrast-Enhanced MRI with an Application to MR Renography
Thursday, 5 November 2009   by www.ncbi.nlm.nih.gov    
MRI Resources 
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ContrastForum -
related threads
 
Contrast is the relative difference of signal intensities in two adjacent regions of an image.
Due to the T1 and T2 relaxation properties in magnetic resonance imaging, differentiation between various tissues in the body is possible. Tissue contrast is affected by not only the T1 and T2 values of specific tissues, but also the differences in the magnetic field strength, temperature changes, and many other factors. Good tissue contrast relies on optimal selection of appropriate pulse sequences (spin echo, inversion recovery, gradient echo, turbo sequences and slice profile).
Important pulse sequence parameters are TR (repetition time), TE (time to echo or echo time), TI (time for inversion or inversion time) and flip angle. They are associated with such parameters as proton density and T1 or T2 relaxation times. The values of these parameters are influenced differently by different tissues and by healthy and diseased sections of the same tissue.
For the T1 weighting it is important to select a correct TR or TI. T2 weighted images depend on a correct choice of the TE. Tissues vary in their T1 and T2 times, which are manipulated in MRI by selection of TR, TI, and TE, respectively. Flip angles mainly affect the strength of the signal measured, but also affect the TR/TI/TE parameters.
Conditions necessary to produce different weighted images:
T1 Weighted Image: TR value equal or less than the tissue specific T1 time - TE value less than the tissue specific T2 time.
T2 Weighted Image: TR value much greater than the tissue specific T1 time - TE value greater or equal than the tissue specific T2 time.
Proton Density Weighted Image: TR value much greater than the tissue specific T1 time - TE value less than the tissue specific T2 time.

See also Image Contrast Characteristics, Contrast Reversal, Contrast Resolution, and Contrast to Noise Ratio.
 
Images, Movies, Sliders:
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Courtesy of  Robert R. Edelman

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 Brain MRI Inversion Recovery  Open this link in a new window
    
 
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Further Reading:
  Basics:
Magnetic resonance imaging
   by www.scholarpedia.org    
MRI's inside story
Thursday, 4 December 2003   by www.economist.com    
Image Characteristics and Quality
   by www.sprawls.org    
  News & More:
A natural boost for MRI scans
Monday, 21 October 2013   by www.eurekalert.org    
A groundbreaking new graphene-based MRI contrast agent
Friday, 8 June 2012   by www.nanowerk.com    
New MRI Chemical Offers Amazing Contrast
Friday, 22 January 2010   by news.softpedia.com    
MRI Resources 
Breast MRI - Societies - Resources - Abdominal Imaging - Musculoskeletal and Joint MRI - Nerve Stimulator
 
Signa HDx 1.5T™InfoSheet: - Devices -
Intro, 
Types of Magnets, 
Overview, 
etc.
 
www.vitalcom.com/euen/mri/products/signa-hdx-15t/index.html From GE Healthcare;
The GE Signa HDx MRI system is a whole body magnetic resonance scanner designed to support high resolution, high signal to noise ratio, and short scan times.
The 1.5T Signa HDx MR Systems is a modification of the currently marketed GE 1.5T machines, with the main difference being the change to the receive chain architecture that includes a thirty two independent receive channels, and allows for future expansion in 16 channel increments. The overall system has been improved with a simplified user interface and a single 23" liquid crystal display, improved multi channel surface coil connectivity, and an improved image reconstruction architecture known as the Volume Recon Engine (VRE).
Device Information and Specification
CLINICAL APPLICATION
Whole body
CONFIGURATION
Compact short bore
Possible
SYNCHRONIZATION
ECG/peripheral, respiratory gating, (SmartPrep, SmartStep)
PULSE SEQUENCES
Standard: SE, IR, 2D/3D GRE and SPGR, Angiography: 2D/3D TOF, 2D/3D Phase Contrast; 2D/3D FSE, 2D/3D FGRE and FSPGR, SSFP, FLAIR, EPI, optional: 2D/3D Fiesta, FGRET, Spiral, Tensor,
IMAGING MODES
2D single slice, multi slice, and 3D volume images, multi slab, cine
1 cm to 48 cm continuous
2D 0.7 mm to 20 mm; 3D 0.1 mm to 5 mm
1028 x 1024
MEASURING MATRIX
128x512 steps 32 phase encode
PIXEL INTENSITY
256 gray levels
POWER REQUIREMENTS
480 or 380/415
COOLING SYSTEM TYPE
Closed-loop water-cooled gradient
CRYOGEN USE, L/hr
less than 0.03 L/hr liquid helium
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Signa HDx 3.0T™InfoSheet: - Devices -
Intro, 
Types of Magnets, 
Overview, 
etc.
 
gehealthcare.com/euen/mri/products/signa-hdx-3t/index.html From GE Healthcare;
The Signa HDx MRI system is GE's leading edge whole body magnetic resonance scanner designed to support high resolution, high signal to noise ratio, and short scan times.
Signa HDx 3.0T offers new technologies like ultra-fast image reconstruction through the new XVRE recon engine, advancements in parallel imaging algorithms and the broadest range of premium applications. The HD applications, PROPELLER (high-quality brain imaging extremely resistant to motion artifacts), TRICKS (contrast-enhanced angiographic vascular lower leg imaging), VIBRANT (for breast MRI), LAVA (high resolution liver imaging with shorter breath holds and better organ coverage) and MR Echo (high-definition cardiac images in real time) offer unique capabilities.
Device Information and Specification
CLINICAL APPLICATION
Whole body
CONFIGURATION
Compact short bore
Head and body coil, T/R quadrature head; optional coils e.g., T/R phased array extremity abdomen, spine, breast, knee, shoulder, cardiac imaging coils
SYNCHRONIZATION
ECG/peripheral, respiratory gating
PULSE SEQUENCES
SE, IR, 2D/3D GRE, RF-spoiled GRE, 2DFGRE, 2DFSPGR, 3DFGRE, 3DFSPGR, 3DTOFGRE, 3DFSPGR, 2DFSE, 2DFSE-XL, 2DFSE-IR, T1-FLAIR, SSFSE, EPI, DW-EPI, BRAVO, Angiography: 2D/3D TOF, 2D/3D phase contrast vascular
IMAGING MODES
Single, multislice, volume study, fast scan, multi slab, cine, localizer
1 cm to 40 cm continuous
2D 0.5 mm; 3D 0.1 mm
1024 x 1024
PIXEL INTENSITY
256 gray levels
60 cm
MAGNET WEIGHT
12000 kg
H*W*D
240 x 2216,6 x 201,6 cm
POWER REQUIREMENTS
480 or 380/415, 3 phase ||
COOLING SYSTEM TYPE
Closed-loop water-cooled grad.
0.03 L/hr helium
STRENGTH
23 - 50 mT/m
80 - 150 mT/m/ms
5-GAUSS FRINGE FIELD
2.8 m / 5.0 m
second and high order
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MAGNETOM Skyra
 
www.healthcare.siemens.com/magnetic-resonance-imaging/0-35-to-1-5t-mri-scanner/magnetom-skyra/ From Siemens Medical Systems; Received FDA clearance in 2010.
MAGNETOM Skyra is a top-of-the-line, patient friendly wide bore 3 Tesla MRI system.
The system is equipped with the Tim 4G and Dot system (Total imaging matrix and Day optimizing throughput), to enhance both productivity and image quality with the complete range of advanced applications for clinical routine and research. Tim 4G features lighter, trimmer MRI coils that take up less space inside the magnet but deliver a high coil element density with increased signal to noise ratio and the possibility to use high iPAT factors.
Device Information and Specification
CLINICAL APPLICATION
Whole Body
CONFIGURATION
Open bore
3 Tesla
Head, spine, torso/ body coil, neurovascular, cardiac, neck, shoulder, knee, wrist, foot//ankle and multi-purpose flex coils. Peripheral vascular, breast, shoulder.
CHANNELS (min. / max. configuration)
48, 64, 128
Chemical shift imaging, single voxel spectroscopy
IMAGING TECHNIQUES
iPAT, mSENSE and GRAPPA (image, k-space),CAIPIRINHA (k-space), noncontrast angiography, plaque imaging, radial motion compensation, Dixon
MINIMUM TR
3D T1 spoiled GRE: 0.95 (256 matrix)
MINIMUM TE
3D T1 spoiled GRE: 0.22 (256 matrix), Ultra-short TE
FOV
0.5 - 50 cm
BORE DIAMETER
or W x H
At isocenter: L-R 70 cm, A-P (with table) 55 cm
TABLE CAPACITY
250 kg
MAGNET WEIGHT (gantry included)
5768 kg
DIMENSION H*W*D (gantry included)
173 x 231 x 219 cm
5-GAUSS FRINGE FIELD
2.6 m / 4.6 m
CRYOGEN USE
Zero boil off rate, approx. 10 years
COOLING SYSTEM
Water; single cryogen, 2 stage refrigeration
up to 200 T/m/s
MAX. AMPLITUDE
45 mT/m
3 linear with 20 coils, 5 nonlinear 2nd-order
POWER REQUIREMENTS
380 / 400 / 420 / 440 / 460 / 480 V, 3-phase + ground; 110 kVA
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