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 'Gradient Strength' 
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Gradient Strength
 
The amplitude of the gradient field (measured in mT/m).
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BandwidthForum -
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(BW) Bandwidth is a measure of frequency range, the range between the highest and lowest frequency allowed in the signal. For analog signals, which can be mathematically viewed as a function of time, bandwidth is the width, measured in Hertz of a frequency range in which the signal's Fourier transform is nonzero.
The receiver (or acquisition) bandwidth (rBW) is the range of frequencies accepted by the receiver to sample the MR signal. The receiver bandwidth is changeable (see also acronyms for 'bandwidth' from different manufacturers) and has a direct relationship to the signal to noise ratio (SNR) (SNR = 1/squareroot (rBW). The bandwidth depends on the readout (or frequency encoding) gradient strength and the data sampling rate (or dwell time).
Bandwidth is defined by BW = Sampling Rate/Number of Samples.
A smaller bandwidth improves SNR, but can cause spatial distortions, also increases the chemical shift. A larger bandwidth reduces SNR (more noise from the outskirts of the spectrum), but allows faster imaging.
The transmit bandwidth refers to the RF excitation pulse required for slice selection in a pulse sequence. The slice thickness is proportional to the bandwidth of the RF pulse (and inversely proportional to the applied gradient strength). Lowering the pulse bandwidth can reduce the slice thickness.
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A higher bandwidth is used for the reduction of chemical shift artifacts (lower bandwidth - more chemical shift - longer dwell time - but better signal to noise ratio). Narrow receive bandwidths accentuate this water fat shift by assigning a smaller number of frequencies across the MRI image. This effect is much more significant on higher field strengths. At 1.5 T, fat and water precess 220 Hz apart, which results in a higher shift than in Low Field MRI.
Lower bandwidth (measured in Hz) = higher water fat shift (measured in pixel shift).

See also Aliasing, Aliasing Artifact, Frequency Encoding, and Chemical Shift Artifact.
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Further Reading:
  Basics:
Bandwidth
   by en.wikipedia.org    
  News & More:
Automated Quality Assurance for Magnetic Resonance Image with Extensions to Diffusion Tensor Imaging(.pdf)
   by scholar.lib.vt.edu    
A Real-Time Navigator Approach to Compensating for Motion Artifacts in Coronary Magnetic Resonance Angiography
   by www.cs.nyu.edu    
MRI Resources 
DICOM - RIS - Absorption and Emission - Veterinary MRI - MRI Reimbursement - Process Analysis
 
Breast MRIMRI Resource Directory:
 - Breast MRI -
 
(MR mammography) Magnetic resonance imaging of the breast is particularly useful in evaluation of newly diagnosed breast cancer, in women whose breast tissue is mammographically very dense and for screening in women with a high lifetime risk of breast cancer because of their family history or genetic disposition.
Breast MRI can be performed on all standard whole body magnets at a field strength of 0.5 T - 1.5 Tesla. Powerful gradient strengths over 15 mT/m will help to improve the balance between spatial resolution, scanning speed, and volume coverage. The use of a dedicated bilateral breast coil is obligatory.
Malignant lesions release angiogenic factors that increase local vessel density and vessel permeability. Breast cancer is detectable due to the strong enhancement in dynamic breast imaging that peaks early (about 1-2 min.) after contrast medium injection. If breast cancer is suspected, a breast biopsy may be necessary to secure the diagnosis.

See also Magnetic Resonance Imaging MRI, Biopsy and MR Guided Interventions.

Requirements in breast MRI procedures:
Both breasts must be measured without gaps.
Temporal resolution should be sufficient to allow early imaging after contrast agent with dynamic imaging every 60-120 sec.
For the best possible detection of enhancement fat signal should be eliminated either by image subtraction or by spectrally selective fat saturation.
Thin slices are necessary to assure absence of partial volume effects.
Imaging should be performed with a spatial resolution in plane less than 1 mm.

For Ultrasound Imaging (USI) see Breast Ultrasound at Medical-Ultrasound-Imaging.com.

See also the related poll result: 'MRI will have replaced 50% of x-ray exams by'
 
Images, Movies, Sliders:
 Breast MRI Images T2 And T1  Open this link in a new window
      
 Breast MRI Images T2 And T1 Pre - Post Contrast  Open this link in a new window
 Breast MRI Images T1 Pre - Post Contrast  Open this link in a new window
      
 
Radiology-tip.comradMammography,  Breast Imaging
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Medical-Ultrasound-Imaging.comBreast Ultrasound
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• View the DATABASE results for 'Breast MRI' (13).Open this link in a new window


• View the NEWS results for 'Breast MRI' (41).Open this link in a new window.
 
Further Reading:
  Basics:
New Screening Guidelines for Women at High Risk for Breast Cancer
Wednesday, 26 September 2007   by www.newswise.com    
CONTRAST-ENHANCED MRI OF THE BREAST(.pdf)
MRI Improves Breast Cancer Screening in Older BRCA Carriers
Monday, 5 January 2015   by www.cancernetwork.com    
  News & More:
Technology advances in breast cancer screenings lead to early diagnosis
Friday, 6 October 2023   by ksltv.com    
Are synthetic contrast-enhanced breast MRI images as good as the real thing?
Friday, 18 November 2022   by healthimaging.com    
Abbreviated breast MRI protocols not as cost-effective as promised, new study shows
Wednesday, 20 July 2022   by healthimaging.com    
Deep learning poised to improve breast cancer imaging
Thursday, 24 February 2022   by www.eurekalert.org    
Pre-Operative Breast MRI Can Help Identify Patients Likely to Experience Nipple-Sparing Mastectomy Risks
Wednesday, 7 April 2021   by www.diagnosticimaging.com    
Breast cancer screening recalls: simple MRI measurement could avoid 30% of biopsies
Monday, 1 March 2021   by www.eurekalert.org    
A Comparison of Methods for High-Spatial-Resolution Diffusion-weighted Imaging in Breast MRI
Tuesday, 25 August 2020   by pubs.rsna.org    
Pre-Operative Breast MRI Diagnoses More Cancers in Women with DCIS
Thursday, 9 July 2020   by www.diagnosticimaging.com    
Breast MRI and tumour biology predict axillary lymph node response to neoadjuvant chemotherapy for breast cancer
Thursday, 26 December 2019   by cancerimagingjournal.biomedcentral.com    
Breast MRI Coding Gets an Overhaul in 2019
Wednesday, 9 January 2019   by www.aapc.com    
How accurate are volumetric software programs when compared to breast MRI?
Thursday, 27 July 2017   by www.radiologybusiness.com    
Additional Breast Cancer Tumors Found on MRI After Mammography May Be Larger, More Aggressive
Wednesday, 9 December 2015   by www.oncologynurseadvisor.com    
Preoperative MRI May Overdiagnose Contralateral Breast Cancer
Wednesday, 2 December 2015   by www.cancertherapyadvisor.com    
BI-RADS and breast MRI useful in predicting malignancy
Wednesday, 30 May 2012   by www.oncologynurseadvisor.com    
Searchterm 'Gradient Strength' was also found in the following service: 
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Chemical Shift ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Please note that there are different common names for this artifact.
Artifact Information
NAME
Chemical shift, black boundary, spatial misregistration, relief
DESCRIPTION
Black or bright band
During frequency encoding, fat protons precess slower than water protons in the same slice because of their magnetic shielding. Through the difference in resonance frequency between water and fat, protons at the same location are misregistrated (dislocated) by the Fourier transformation, when converting MRI signals from frequency to spatial domain. This chemical shift misregistration cause accentuation of any fat-water interfaces along the frequency axis and may be mistaken for pathology. Where fat and water are in the same location, this artifact can be seen as a bright or dark band at the edge of the anatomy.
Protons in fat and water molecules are separated by a chemical shift of about 3.5 ppm. The actual shift in Hertz (Hz) depends on the magnetic field strength of the magnet being used. Higher field strength increases the misregistration, while in contrast a higher gradient strength has a positive effect. For a 0.3 T system operating at 12.8 MHz the shift will be 44.8 Hz compared with a 223.6 Hz shift for a 1.5 T system operating at 63.9 MHz.
mri safety guidance
Image Guidance
For artifact reduction helps a smaller water fat shift (higher bandwidth), a higher matrix, an in phase TE or a spin echo technique. Since the misregistration offset is present in the read out axis the patient may be rescanned with this axis parallel to the fat-water interface. Steeper gradient may be employed to reduce the chemical shift offset in mm. Another strategy is to employ specialized pulse sequences such as fat saturation or inversion recovery imaging. Fat suppression techniques eliminate chemical shift artifacts caused by the lack of fat signal.

See also Black Boundary Artifact and Magnetic Resonance Spectroscopy.
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• View the DATABASE results for 'Chemical Shift Artifact' (7).Open this link in a new window

 
Further Reading:
  Basics:
MRI Artifact Gallery
   by chickscope.beckman.uiuc.edu    
  News & More:
What is chemical shift artefact? Why does it occur? How many Hz at 1.5 T?
   by www.revisemri.com    
Abdominal MRI at 3.0 T: The Basics Revisited
Wednesday, 20 July 2005   by www.ajronline.org    
MRI Resources 
Implant and Prosthesis - IR - General - Collections - MRCP - Spine MRI
 
Echo Planar ImagingInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.MRI Resource Directory:
 - Sequences -
 
Echo Planar Imaging Timing Diagram (EPI) Echo planar imaging is one of the early magnetic resonance imaging sequences (also known as Intascan), used in applications like diffusion, perfusion, and functional magnetic resonance imaging. Other sequences acquire one k-space line at each phase encoding step. When the echo planar imaging acquisition strategy is used, the complete image is formed from a single data sample (all k-space lines are measured in one repetition time) of a gradient echo or spin echo sequence (see single shot technique) with an acquisition time of about 20 to 100 ms. The pulse sequence timing diagram illustrates an echo planar imaging sequence from spin echo type with eight echo train pulses. (See also Pulse Sequence Timing Diagram, for a description of the components.)
In case of a gradient echo based EPI sequence the initial part is very similar to a standard gradient echo sequence. By periodically fast reversing the readout or frequency encoding gradient, a train of echoes is generated.
EPI requires higher performance from the MRI scanner like much larger gradient amplitudes. The scan time is dependent on the spatial resolution required, the strength of the applied gradient fields and the time the machine needs to ramp the gradients.
In EPI, there is water fat shift in the phase encoding direction due to phase accumulations. To minimize water fat shift (WFS) in the phase direction fat suppression and a wide bandwidth (BW) are selected. On a typical EPI sequence, there is virtually no time at all for the flat top of the gradient waveform. The problem is solved by "ramp sampling" through most of the rise and fall time to improve image resolution.
The benefits of the fast imaging time are not without cost. EPI is relatively demanding on the scanner hardware, in particular on gradient strengths, gradient switching times, and receiver bandwidth. In addition, EPI is extremely sensitive to image artifacts and distortions.
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• View the NEWS results for 'Echo Planar Imaging' (1).Open this link in a new window.
 
Further Reading:
  Basics:
New Imaging Method Makes Brain Scans 7 Times Faster
Sunday, 9 January 2011   by www.dailytech.com    
MRI Resources 
Corporations - Spine MRI - MRI Technician and Technologist Schools - MR Guided Interventions - MRI Training Courses - Databases
 
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