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Single Shot Technique
 
In single shot techniques (used for EPI, TSE, FSE, RARE, HASTE), the entire raw data set is acquired with a single excitation pulse. The magnetization of a fully relaxed spin system is used. Each of the subsequent echoes is given a different phase encoding. For improved SNR, spatial resolution or FOV, the needed raw data are acquired over a number of sequence repetitions. Each repetition then collects a fraction of the complete raw data set. Only slightly more than a half of the raw data is acquired. The image is obtained through half Fourier reconstruction.
A single shot sequence is useful in cases where movement is to expect e.g. in abdominal Imaging or fetal MRI.
See also Half Fourier Acquisition Single Shot Turbo Spin Echo.
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• Related Searches:
    • Fetal MRI
    • Half Fourier
    • Segmented HASTE
    • Point Resolved Spectroscopy
    • Parallel Imaging Technique
 
Further Reading:
  Basics:
Scanning the Abdomen
   by www.mrprotocols.com    
Clinical evaluation of a speed optimized T2 weighted fast spin echo sequence at 3.0 T using variable flip angle refocusing, half-Fourier acquisition and parallel imaging
Wednesday, 25 October 2006
MRI Resources 
Hospitals - Contrast Agents - DICOM - Cardiovascular Imaging - Chemistry - Directories
 
Artifact by Patient MovementInfoSheet: - 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 Motion, movement
DESCRIPTION Blurring, ghosting
REASON Patient movement
HELP Fast scan techniques

Patient movement during the scans are often an imaging problem. Artifacts from patient movement are widely varied due to a dependence when during k-space filling the motion occurs. When the patient moving causes only in the last few seconds of the scan at that time the outside edges of K-space were being filled, and as a result the artifact does not overly affect the image (there are only fine lines).


Image Guidance
A good cooperation between the patient and the operator is the best way to avoid these artifacts, in difficult cases a sedative may help. If a compliance of the patient is not possible (e.g. pain, stroke, or consciousness), choose fast scan methods like gradient echo or single shot technique.
See also Motion Artifact and Phase Encoded Motion Artifact.

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Further Reading:
  News & More:
Patient movement during MRI: Additional points to ponder
Tuesday, 5 January 2016   by www.healthimaging.com    
MRI Resources 
Claustrophobia - Pregnancy - Safety Training - Crystallography - Portals - Stent
 
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 DATABASE results for 'Echo Planar Imaging' (19).Open this link in a new window


• 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    
Searchterm 'Single Shot Technique' was also found in the following service: 
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Fetal MRI
 
Ultrasound imaging is the primary fetal monitoring modality during pregnancy, nevertheless fetal MRI is increasingly used to image anatomical regions and structures difficult to see with sonography. Given its long record of safety, utility, and cost-effectiveness, ultrasound will remain the modality of first choice in fetal screening. However, MRI is beginning to fill a niche in situations where ultrasound does not provide enough information to diagnose abnormalities before the baby’s birth. Magnetic resonance imaging of the fetus provides multiplanar views also in sub-optimal positions, better characterization of anatomic details of e.g. the fetal brain, and information for planning the mode of delivery and airway management at birth.
Indications:
Fetal anomalies
Maternal tumors
Pelvimetry
Examinations of the placenta
Modern fetal MRI requires no sedatives or muscle relaxants to control fetal movement. Ultrafast MRI techniques (e.g., single shot techniques like Half Fourier Acquisition Single shot Turbo spin Echo HASTE) enable images to be acquired in less than one second to eliminate fetal motion. Such technology has led to increased usage of fetal MRI, which can lead to earlier diagnosis of conditions affecting the baby and has proven useful in planning fetal surgery and designing postnatal treatments. As MR technology continues to improve, more advances in the prenatal diagnosis and treatment of fetal abnormalities are to expect. More advances in in-utero interventions are likely as well. Eventually, fetal MRI may replace even some prenatal tests that require invasive procedures such as amniocentesis.

For Ultrasound Imaging (USI) see Fetal Ultrasound at US-TIP.com.
 
Images, Movies, Sliders:
 Normal Fetus  Open this link in a new window
    

Courtesy of  Robert R. Edelman
 Pregnancy and Small Bowel Obstruction  Open this link in a new window
    

Courtesy of  Robert R. Edelman
 Fetus (Brain) and Dermoid in Mother  Open this link in a new window
      

Courtesy of  Robert R. Edelman

 
Radiology-tip.comRadiation Safety
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Radiology-tip.comFetal Ultrasound,  4D Ultrasound
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• View the DATABASE results for 'Fetal MRI' (5).Open this link in a new window


• View the NEWS results for 'Fetal MRI' (2).Open this link in a new window.
 
Further Reading:
  Basics:
Advancing MRI scans for foetal development
Wednesday, 27 November 2013   by cordis.europa.eu    
Untangling the Maze, Imaging the Fetus
Tuesday, 30 September 2014   by www.newswise.com    
In fetal MRI, 3T shown to have it all over 1.5T
Tuesday, 12 January 2016   by www.healthimaging.com    
  News & More:
3-T MRI advancing on ultrasound for imaging fetal abnormalities
Monday, 20 April 2015   by www.eurekalert.org    
Real-time MRI helps doctors assess beating heart in fetus
Thursday, 29 September 2005   by www.eurekalert.org    
Post-Mortem MRI Accurate for Fetuses, Newborns, Infants
Thursday, 16 May 2013   by www.doctorslounge.com    
Ultrasensitive Detector Pinpoints Big Problem in Tiny Fetal Heart
Tuesday, 6 April 2010   by www.sciencedaily.com    
Siemens Introduces MRI Education Tool For Pediatric Patients
Monday, 27 October 2014   by weill.cornell.edu    
MRI Resources 
Research Labs - Distributors - Lung Imaging - Devices - Artifacts - Manufacturers
 
Liver ImagingForum -
related threadsMRI Resource Directory:
 - Liver Imaging -
 
Liver imaging can be performed with sonography, computed tomography (CT) and magnetic resonance imaging (MRI). Ultrasound is, caused by the easy access, still the first-line imaging method of choice; CT and MRI are applied whenever ultrasound imaging yields vague results. Indications are the characterization of metastases and primary liver tumors e.g., benign lesions such as focal nodular hyperplasia (FNH), adenoma, hemangioma and malignant lesions (cancer) such as hepatocellular carcinomas (HCC). The decision, which medical imaging modality is more suitable, MRI or CT, is dependent on the different factors. CT is less costly and more widely available; modern multislice scanners provide high spatial resolution and short scan times but has the disadvantage of radiation exposure.
With the introduction of high performance MR systems and advanced sequences the image quality of MRI for the liver has gained substantially. Fast spin echo or single shot techniques, often combined with fat suppression, are the most common T2 weighted sequences used in liver MRI procedures. Spoiled gradient echo sequences are used as ideal T1 weighted sequences for evaluating of the liver. The repetition time (TR) can be sufficiently long to acquire enough sections covering the entire liver in one pass, and to provide good signal to noise. The TE should be the shortest in phase echo time (TE), which provides strong T1 weighting, minimizes magnetic susceptibility effects, and permits acquisition within one breath hold to cover the whole liver. A flip angle of 80° provides good T1 weighting and less of power deposition and tissue saturation than a larger flip angle that would provide comparable T1 weighting.
Liver MRI is very dependent on the administration of contrast agents, especially when detection and characterization of focal lesions are the issues. Liver MRI combined with MRCP is useful to evaluate patients with hepatic and biliary disease.
Gadolinium chelates are typical non-specific extracellular agents diffusing rapidly to the extravascular space of tissues being cleared by glomerular filtration at the kidney. These characteristics are somewhat problematic when a large organ with a huge interstitial space like the liver is imaged. These agents provide a small temporal imaging window (seconds), after which they begin to diffuse to the interstitial space not only of healthy liver cells but also of lesions, reducing the contrast gradient necessary for easy lesion detection. Dynamic MRI with multiple phases after i.v. contrast media (Gd chelates), with arterial, portal and late phase images (similar to CT) provides additional information.
An additional advantage of MRI is the availability of liver-specific contrast agents (see also Hepatobiliary Contrast Agents). Gd-EOB-DTPA (gadoxetate disodium, Gadolinium ethoxybenzyl dimeglumine, EOVIST Injection, brand name in other countries is Primovist) is a gadolinium-based MRI contrast agent approved by the FDA for the detection and characterization of known or suspected focal liver lesions.
Gd-EOB-DTPA provides dynamic phases after intravenous injection, similarly to non-specific gadolinium chelates, and distributes into the hepatocytes and bile ducts during the hepatobiliary phase. It has up to 50% hepatobiliary excretion in the normal liver.
Since ferumoxides are not eliminated by the kidney, they possess long plasmatic half-lives, allowing circulation for several minutes in the vascular space. The uptake process is dependent on the total size of the particle being quicker for larger particles with a size of the range of 150 nm (called superparamagnetic iron oxide). The smaller ones, possessing a total particle size in the order of 30 nm, are called ultrasmall superparamagnetic iron oxide particles and they suffer a slower uptake by RES cells. Intracellular contrast agents used in liver MRI are primarily targeted to the normal liver parenchyma and not to pathological cells. Currently, iron oxide based MRI contrast agents are not marketed.
Beyond contrast enhanced MRI, the detection of fatty liver disease and iron overload has clinical significance due to the potential for evolution into cirrhosis and hepatocellular carcinoma. Imaging-based liver fat quantification (see also Dixon) provides noninvasively information about fat metabolism; chemical shift imaging or T2*-weighted imaging allow the quantification of hepatic iron concentration. See also Abdominal Imaging, Primovist™, Liver Acquisition with Volume Acquisition (LAVA), T1W High Resolution Isotropic Volume Examination (THRIVE) and Bolus Injection.

For Ultrasound Imaging (USI) see Liver Sonography at US-TIP.com.
 
Images, Movies, Sliders:
 Anatomic Imaging of the Liver  Open this link in a new window
      

 MRI Liver T2 TSE  Open this link in a new window
    
 
Radiology-tip.comAbdomen CT,  Biliary Contrast Agents
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Radiology-tip.comLiver Sonography,  Vascular Ultrasound Contrast Agents
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• View the DATABASE results for 'Liver Imaging' (13).Open this link in a new window


• View the NEWS results for 'Liver Imaging' (10).Open this link in a new window.
 
Further Reading:
  Basics:
Contrast MRI Best at Finding Liver Trouble - But Timing Matters
Sunday, 6 March 2011   by www.searchmedica.com    
MR contrast agents: Applications in hepatobiliary imaging
Thursday, 11 November 2010   by www.appliedradiology.com    
Elastography: A Useful Method in Depicting Liver Hardness
Thursday, 15 April 2010   by www.sciencedaily.com    
Iron overload: accuracy of in-phase and out-of-phase MRI as a quick method to evaluate liver iron load in haematological malignancies and chronic liver disease
Friday, 1 June 2012   by www.ncbi.nlm.nih.gov    
MAGNETIC RESONANCE IMAGING OF FOCAL LIVER LESIONS(.pdf)
2002
  News & More:
EORTC study aims to qualify ADC as predictive imaging biomarker in preoperative regimens
Monday, 4 January 2016   by www.eurekalert.org    
MRI effectively measures hemochromatosis iron burden
Saturday, 3 October 2015   by medicalxpress.com    
Total body iron balance: Liver MRI better than biopsy
Sunday, 15 March 2015   by www.eurekalert.org    
Radiologists Offer Non-surgical Treatment For Early-stage Liver Cancer
Saturday, 5 March 2005   by www.sciencedaily.com    
Perspectum Diagnostics Announces FDA Clearance for LiverMultiscan MR Imaging Device
Thursday, 12 November 2015   by www.fiercemedicaldevices.com    
MRI Resources 
Spine MRI - Image Quality - PACS - Safety Training - Implant and Prosthesis - Hospitals
 
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