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Time to Peak
 
(TTP) A time to peak map shows the regional distribution of the time needed to the minimum perfusion signal, either gray scale or color-coded.
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MRI Resources 
Musculoskeletal and Joint MRI - Fluorescence - MRI Reimbursement - Safety pool - Guidance - Lung Imaging
 
Perfusion ImagingForum -
related threadsInfoSheet: - Sequences - 
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(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 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
MRI Resources 
General - Examinations - MRI Technician and Technologist Schools - PACS - MRI Centers - Spectroscopy
 
Free Induction Decay
 
(FID) A free induction decay curve is generated as excited nuclei relax. The amplitude of the FID signal becomes smaller over time as net magnetization returns to equilibrium. If transverse magnetization of the spins is produced, e.g. by a 90° pulse, a transient MR signal will result that will decay toward zero with a characteristic time constant T2 (or T2*); this decaying signal is the free induction decay.
The signal peaks of the echoes fall onto this T2 decay curve, while at each echo the signals arise and decay with T2*. The typical T2 relaxation times being of the order of 5-200 ms in the human body. The first part of the FID is not observable (named the 'receiver dead time') caused by residual effects of the powerful exciting radio frequency pulse on the electronics of the receiver.
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Further Reading:
  Basics:
Free induction decay
   by en.wikipedia.org    
  News & More:
Magnetic resonance imaging
   by www.scholarpedia.org    
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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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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    
MRI Resources 
Mobile MRI Rental - Supplies - Claustrophobia - Education pool - Online Books - Spectroscopy
 
Magnetic Resonance SpectroscopyMRI Resource Directory:
 - Spectroscopy pool -
 
(MRS / MRSI - Magnetic Resonance Spectroscopic Imaging) A method using the NMR phenomenon to identify the chemical state of various elements without destroying the sample. MRS therefore provides information about the chemical composition of the tissues and the changes in chemical composition, which may occur with disease processes.
Although MRS is primarily employed as a research tool and has yet to achieve widespread acceptance in routine clinical practice, there is a growing realization that a noninvasive technique, which monitors disease biochemistry can provide important new information for the clinician.
The underlying principle of MRS is that atomic nuclei are surrounded by a cloud of electrons, which very slightly shield the nucleus from any external magnetic field. As the structure of the electron cloud is specific to an individual molecule or compound, then the magnitude of this screening effect is also a characteristic of the chemical environment of individual nuclei.
In view of the fact that the resonant frequency is proportional to the magnetic field that it experiences, it follows that the resonant frequency will be determined not only by the external applied field, but also by the small field shift generated by the electron cloud. This shift in frequency is called the chemical shift (see also Chemical Shift). It should be noted that chemical shift is a very small effect, usually expressed in ppm of the main frequency. In order to resolve the different chemical species, it is therefore necessary to achieve very high levels of homogeneity of the main magnetic field B0. Spectra from humans usually require shimming the magnet to approximately one part in 100. High resolution spectra of liquid samples demand a homogeneity of about one part in 1000.
In addition to the effects of factors such as relaxation times that can affect the NMR signal, as seen in magnetic resonance imaging, effects such as J-modulation or the transfer of magnetization after selective excitation of particular spectral lines can affect the relative strengths of spectral lines.
In the context of human MRS, two nuclei are of particular interest - H-1 and P-31. (PMRS - Proton Magnetic Resonance Spectroscopy) PMRS is mainly employed in studies of the brain where prominent peaks arise from NAA, choline containing compounds, creatine and creatine phosphate, myo-inositol and, if present, lactate; phosphorus 31 MR spectroscopy detects compounds involved in energy metabolism (creatine phosphate, adenosine triphosphate and inorganic phosphate) and certain compounds related to membrane synthesis and degradation. The frequencies of certain lines may also be affected by factors such as the local pH. It is also possible to determine intracellular pH because the inorganic phosphate peak position is pH sensitive.
If the field is uniform over the volume of the sample, "similar" nuclei will contribute a particular frequency component to the detected response signal irrespective of their individual positions in the sample. Since nuclei of different elements resonate at different frequencies, each element in the sample contributes a different frequency component. A chemical analysis can then be conducted by analyzing the MR response signal into its frequency components.

See also Spectroscopy.
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Further Reading:
  News & More:
Accuracy of Proton Magnetic Resonance Spectroscopy in Distinguishing Neoplastic From Non-neoplastic Brain Lesions
Saturday, 2 December 2023   by www.cureus.com    
MRI Resources 
Safety Training - Artifacts - Liver Imaging - General - Abdominal Imaging - DICOM
 
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