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Result : Searchterm 'Real' found in 4 terms [] and 43 definitions []
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Oversampling
 
Oversampling is the increase in data to avoid aliasing and wrap around artifacts. Aliasing is the incorrectly mapping of tissue signal from outside the FOV to a location inside the FOV. This is caused by the fact, that the acquired k-space frequency data is not sampled density enough.
Oversampling in frequency direction, done by increasing the sampling frequency, prevents this aliasing artifact. The proper frequency based on the sampling theorem (Shannon sampling theorem/Nyquist sampling theorem) must be at least twice the frequency of each frequency component in the incoming signal. All frequency components above this limit will be aliased to frequencies between zero and half of the sampling frequency and combined with the proper signal information, which creates the artifact. Oversampling creates a larger field of view, more data needs to be stored and processed, but this is for modern MRI systems not a real problem. Oversampling in phase direction (no phase wrap), to eliminate wrap around artifacts, by increasing the number of phase encoding steps, results in longer scan/processing times.
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• Related Searches:
    • Wrap Around Artifact
    • Phase Wrapping Artifact
    • Foldover Artifact
    • Number of Signal Averages
    • Sample Imperfection (Artifact)
 
Further Reading:
  Basics:
The Basics of MRI
   by www.cis.rit.edu    
The Scientist and Engineer's Guide to Digital Signal Processing
   by www.dspguide.com    
Searchterm 'Real' was also found in the following services: 
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Radiology  (9) Open this link in a new windowUltrasound  (52) Open this link in a new window
Panorama 0.23T™InfoSheet: - Devices -
Intro, 
Types of Magnets, 
Overview, 
etc.MRI Resource Directory:
 - Devices -
 
www.medical.philips.com/main/products/mri/products/panoramafamily/panorama0.23t_rt/features/ From Philips Medical Systems;
the Panorama 0.23 T, providing a new design optimized for patient comfort, faster reconstruction time than before (300 images/second) and new gradient specifications. Philips' Panorama 0.23 T I/T supports MR-guided interventions, resulting in minimally invasive procedures, more targeted surgery, reduced recovery time and shorter hospital stays. Optional OptoGuide functionality enables real-time needle tracking. Philips' Panorama 0.23 TPanorama 0.2 R/T is the first and only open MRI system to enable radiation therapy planning using MR data sets. The Panorama also features the new and consistent Philips User Interface, an essential element of the Vequion clinical IT family of products and services.
Device Information and Specification
CLINICAL APPLICATION
Whole body
CONFIGURATION
Open MRI/C-arm
Head, head-neck, extremity M-L, neck, body/spine S-XL, shoulder, bilateral breast, wrist, TMJ, flex XS-S-M-L-XL-XXL
SYNCHRONIZATION
ECG/peripheral: Optional/optional, respiratory gating
PULSE SEQUENCES
SE, FE, IR, FFE, DEFFE, DESE, TSE, DETSE, Single shot SE, DRIVE, Balanced FFE, MRCP, Fluid Attenuated Inversion Recovery, Turbo FLAIR, IR-TSE, T1-STIR TSE, T2-STIR TSE, Diffusion Imaging, 3D SE, 3D FFE, MTC;; Angiography: CE-ANGIO, MRA 2D, 3D TOF
IMAGING MODES
Single, multislice, volume study, dynamic, SIMEX, multi chunk 3D, multiple stacks
TR
Min. 6.2 msec
TE
Min. 2.8 msec
SINGLE/MULTI SLICE
50 slices/sec
0.4 cm - 40 cm
1280 X 1024
MEASURING MATRIX
Up to 512 x 512
PIXEL INTENSITY
256 gray scale
MAGNET TYPE
Resistive/iron core
Open x 46 cm x infinite (side-first patient entry)
MAGNET WEIGHT
13110 kg
H*W*D
196 x 121 x 176 cm
POWER REQUIREMENTS
400/480 V
COOLING SYSTEM TYPE
Closed loop chilled water (chiller included)
N/A
STRENGTH
19 mT/m
5-GAUSS FRINGE FIELD
2.4 m / 3.7 m
Passive/active
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• View the DATABASE results for 'Panorama 0.23T™' (2).Open this link in a new window

 
Further Reading:
  News & More:
Magnetic resonance imaging guided musculoskeletal interventions at 0.23T: Chapter 4. Materials and methods
2002
MRI Resources 
MRI Training Courses - Lung Imaging - Colonography - Breast MRI - Resources - Sequences
 
Perfusion ImagingForum -
related threadsInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
(PWI - Perfusion Weighted Imaging) Perfusion MRI techniques (e.g. PRESTO - Principles of Echo Shifting using a Train of Observations) are sensitive to microscopic levels of blood flow. Contrast enhanced relative cerebral blood volume (rCBV) is the most used perfusion imaging. Both, the ready availability and the T2* susceptibility effects of gadolinium, rather than the T1 shortening effects make gadolinium a suitable agent for use in perfusion imaging. Susceptibility here refers to the loss of MR signal, most marked on T2* (gradient echo)-weighted and T2 (spin echo)-weighted sequences, caused by the magnetic field-distorting effects of paramagnetic substances.
T2* perfusion uses dynamic sequences based on multi or single shot techniques. The T2* (T2) MRI signal drop within or across a brain region is caused by spin dephasing during the rapid passage of contrast agent through the capillary bed. The signal decrease is used to compute the relative perfusion to that region. The bolus through the tissue is only a few seconds, high temporal resolution imaging is required to obtain sequential images during the wash in and wash out of the contrast material and therefore, resolve the first pass of the tracer. Due to the high temporal resolution, processing and calculation of hemodynamic maps are available (including mean transit time (MTT), time to peak (TTP), time of arrival (T0), negative integral (N1) and index.
An important neuroradiological indication for MRI is the evaluation of incipient or acute stroke via perfusion and diffusion imaging. Diffusion imaging can demonstrate the central effect of a stroke on the brain, whereas perfusion imaging visualizes the larger 'second ring' delineating blood flow and blood volume. Qualitative and in some instances quantitative (e.g. quantitative imaging of perfusion using a single subtraction) maps of regional organ perfusion can thus be obtained.
Echo planar and potentially echo volume techniques together with appropriate computing power offer real time images of dynamic variations in water characteristics reflecting perfusion, diffusion, oxygenation (see also Oxygen Mapping) and flow.
Another type of perfusion MR imaging allows the evaluation of myocardial ischemia during pharmacologic stress. After e.g., adenosine infusion, multiple short axis views (see cardiac axes) of the heart are obtained during the administration of gadolinium contrast. Ischemic areas show up as areas of delayed and diminished enhancement. The MRI stress perfusion has been shown to be more accurate than nuclear SPECT exams. Myocardial late enhancement and stress perfusion imaging can also be performed during the same cardiac MRI examination.
 
Images, Movies, Sliders:
 Normal Lung Gd Perfusion MRI  Open this link in a new window
      

Courtesy of  Robert R. Edelman

 Left Circumflex Ischemia First-pass Contrast Enhancement  Open this link in a new window
 
Radiology-tip.comradPerfusion Scintigraphy
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Medical-Ultrasound-Imaging.comBolus Injection
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• View the DATABASE results for 'Perfusion Imaging' (16).Open this link in a new window


• View the NEWS results for 'Perfusion Imaging' (3).Open this link in a new window.
 
Further Reading:
  Basics:
CHAPTER 55: Ischemia
2003
EVALUATION OF HUMAN STROKE BY MR IMAGING
2000
  News & More:
Non-invasive diagnostic procedures for suspected CHD: Search reveals informative evidence
Wednesday, 8 July 2020   by medicalxpress.co    
Implementation of Dual-Source RF Excitation in 3 T MR-Scanners Allows for Nearly Identical ADC Values Compared to 1.5 T MR Scanners in the Abdomen
Wednesday, 29 February 2012   by www.plosone.org    
Motion-compensation of Cardiac Perfusion MRI using a Statistical Texture Ensemble(.pdf)
June 2003   by www.imm.dtu.dk    
Turbo-FLASH Based Arterial Spin Labeled Perfusion MRI at 7 T
Thursday, 20 June 2013   by www.plosone.org    
Measuring Cerebral Blood Flow Using Magnetic Resonance Imaging Techniques
1999   by www.stanford.edu    
Vascular Filters of Functional MRI: Spatial Localization Using BOLD and CBV Contrast
Searchterm 'Real' was also found in the following services: 
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News  (47)  Resources  (9)  Forum  (34)  
 
Receiver turn on ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Artifact Information
NAME
Receiver turn on
DESCRIPTION
Line across the center of the image
REASON
Combination of problems
HELP
Call the service
A receiver turn on artifact (not a true MR signal) appears similarly like a FID signal artifact, except that they extend into the signal-free region, while the FID (a real MR signal) is confined to the projection of the sample along the readout axis.
mri safety guidance
Image Guidance
FID artifacts cannot occur on gradient echo images, but receiver turn on is still possible on gradient echoes.

See also FID Signal Artifact.
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Further Reading:
  Basics:
MRI Artifact Gallery
   by chickscope.beckman.uiuc.edu    
Searchterm 'Real' was also found in the following services: 
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Radiology  (9) Open this link in a new windowUltrasound  (52) Open this link in a new window
Sensitivity EncodingInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
(SENSE) A MRI technique for relevant scan time reduction. The spatial information related to the coils of a receiver array are utilized for reducing conventional Fourier encoding. In principle, SENSE can be applied to any imaging sequence and k-space trajectories. However, it is particularly feasible for Cartesian sampling schemes. In 2D Fourier imaging with common Cartesian sampling of k-space sensitivity encoding by means of a receiver array enables to reduce the number of Fourier encoding steps.
SENSE reconstruction without artifacts relies on accurate knowledge of the individual coil sensitivities. For sensitivity assessment, low-resolution, fully Fourier-encoded reference images are required, obtained with each array element and with a body coil.
The major negative point of parallel imaging techniques is that they diminish SNR in proportion to the numbers of reduction factors. R is the factor by which the number of k-space samples is reduced. In standard Fourier imaging reducing the sampling density results in the reduction of the FOV, causing aliasing. In fact, SENSE reconstruction in the Cartesian case is efficiently performed by first creating one such aliased image for each array element using discrete Fourier transformation (DFT).
The next step then is to create a full-FOV image from the set of intermediate images. To achieve this one must undo the signal superposition underlying the fold-over effect. That is, for each pixel in the reduced FOV the signal contributions from a number of positions in the full FOV need to be separated. These positions form a Cartesian grid corresponding to the size of the reduced FOV.
The advantages are especially true for contrast-enhanced MR imaging such as dynamic liver MRI (liver imaging) , 3 dimensional magnetic resonance angiography (3D MRA), and magnetic resonance cholangiopancreaticography (MRCP).
The excellent scan speed of SENSE allows for acquisition of two separate sets of hepatic MR images within the time regarded as the hepatic arterial-phase (double arterial-phase technique) as well as that of multidetector CT.
SENSE can also increase the time efficiency of spatial signal encoding in 3D MRA. With SENSE, even ultrafast (sub second) 4D MRA can be realized.
For MRCP acquisition, high-resolution 3D MRCP images can be constantly provided by SENSE. This is because SENSE resolves the presence of the severe motion artifacts due to longer acquisition time. Longer acquisition time, which results in diminishing image quality, is the greatest problem for 3D MRCP imaging.
In addition, SENSE reduces the train of gradient echoes in combination with a faster k-space traversal per unit time, thereby dramatically improving the image quality of single shot echo planar imaging (i.e. T2 weighted, diffusion weighted imaging).
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• View the DATABASE results for 'Sensitivity Encoding' (12).Open this link in a new window

 
Further Reading:
  News & More:
Image Characteristics and Quality
   by www.sprawls.org    
MRI Resources 
Claustrophobia - Nerve Stimulator - Hospitals - MRI Centers - DICOM - Musculoskeletal and Joint MRI
 
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