Items tagged “mri”
117 results found
Article
Bright rim sign (DNET)
The bright rim sign, also known as the hyperintense ring sign, is an MRI sign described most frequently in dysembryoplastic neuroepithelial tumors (DNET) but is also seen in some other tumors.
Terminology
Although the sign is most associated with DNETs, and should probably be reserved in case...
Article
Chemical shift artifact
Chemical shift artifact or misregistration is a type of MRI artifact. It is a common finding on some MRI sequences and used in magnetic resonance spectroscopy (MRS). This artifact occurs in the frequency-encoding direction and is due to spatial misregistration of fat and water molecules.
Chemi...
Article
Magic angle effect (MRI artifact)
The magic angle is an MRI artifact that occurs in sequences with a short TE (less than 32 ms) - T1 weighted, proton density weighted, and gradient echo sequences.
It is confined to regions of tightly bound collagen at 54.74° from the main magnetic field (B0), and appears hyperintense, thus pote...
Article
Nephrogenic systemic fibrosis
Nephrogenic systemic fibrosis (NSF), also known as nephrogenic fibrosing dermopathy, occurs almost exclusively in patients with renal impairment and is associated with the administration of gadolinium-based contrast agents (GBCAs) used in MRI.
The American College of Radiology (ACR) has divide...
Article
Phase-encoded motion artifact
Phase-encoded motion artifact is one of many MRI artifacts occurring as a result of tissue/fluid moving during the scan. It manifests as ghosting in the direction of phase-encoding, usually in the direction of the short axis of the image (i.e left to right on axial or coronal brains, and anterio...
Article
Sugar coating
So-called "sugar coating" or zuckerguss (German for sugar icing) refers to the appearance of diffuse linear/sheetlike leptomeningeal contrast enhancement in the brain or spinal cord due to drop metastases or leptomeningeal carcinomatosis. It is seen both as a result of CNS involvement from dista...
Article
Anterior cruciate ligament mucoid degeneration
Anterior cruciate ligament (ACL) mucoid degeneration, along with tears and anterior cruciate ligament ganglion cysts, is a relatively common cause of increased signal within the anterior cruciate ligament (ACL). The appearance can mimic acute or chronic interstitial partial tears of the ACL. How...
Article
Normal myelination
After normal myelination in utero, myelination of the neonatal brain is far from complete. The first myelination is seen as early as the 16th week of gestation, in the column of Burdach, but only really takes off from the 24th week 1. It does not reach maturity until 2 years or so. It correlates...
Article
T1 weighted image
T1 weighted image (also referred to as T1WI or the "spin-lattice" relaxation time) is one of the basic pulse sequences in MRI and demonstrates differences in the T1 relaxation times of tissues.
A T1WI relies upon the longitudinal relaxation of a tissue's net magnetization vector (NMV). Basicall...
Article
B0
The B0 in MRI refers to the main static magnetic field and is measured in teslas (T). The majority of MRI systems in clinical use are 1.5 T, with increasing numbers of 3 T systems being installed. Since 2017, 7 T clinical scanners have been available, see ultrahigh field MRI.
Altering the field...
Article
Larmor frequency
The Larmor frequency and equation are named after the Irish physicist and mathematician Joseph Larmor (1857–1942).
Protons and neutrons pair up in nuclei causing the cancelation of their individual angular momentum. All nuclei also have a spin; those with an odd number of protons and/or neutron...
Article
Net magnetization vector
The net magnetization vector in MRI is the summation of all the magnetic moments of the individual hydrogen nuclei.
In the absence of an external magnetic field, the individual magnetic moments are randomly oriented and since they are in opposition, the net magnetization vector is considered to...
Article
MRI
MRI (an abbreviation of magnetic resonance imaging) is an imaging modality that uses non-ionizing radiation to create useful diagnostic images.
In simple terms, an MRI scanner consists of a large, powerful magnet in which the patient lies. A radio wave antenna is used to send signals to the bod...
Article
Hemorrhage on MRI
Hemorrhage on MRI has highly variable imaging characteristics that depend on:
the age of the blood
the type of hemoglobin present: oxy-, deoxy- or met-
whether or not the red blood cell walls are intact: i.e. intra- vs extracellular
the MRI sequence
Although MRI is often regarded as being i...
Article
Rectal cancer (staging)
Staging of rectal cancer uses the TNM staging system and strongly predicts the success, and rate, of local recurrence following rectal cancer resection. MRI is the modality of choice for the staging of rectal cancer, to guide surgical and non-surgical management options. MRI is used at diagnosis...
Article
Turbo inversion recovery magnitude
Turbo inversion recovery magnitude (TIRM) is an inversion recovery MRI pulse sequence that displays the magnitude of a turbo/fast spin echo, without regard for the phase/polarity of the longitudinal magnetization. This method of image reconstruction is the dominant form of inversion recovery use...
Article
MRI pulse sequence abbreviations
This article contains a list of commonly and less commonly used MRI pulse sequence abbreviations and their meaning. If available, an explanation is included in a separate article.
image weighting
T1
T2
T2*: T2 star
PD: proton density
DWI: diffusion-weighted imaging and ADC: apparent diff...
Article
Testicular seminoma
Testicular seminomas are a type of germ cell tumor and the most common testicular tumor, accounting for ~45% of all primary testicular tumors. This article concerns only testicular seminomas; however, seminomas can arise outside of the testis, most often within the anterior mediastinum (see arti...
Article
Myo-inositol peak
Myo-inositol is one of the compounds images with MR spectroscopy (MRS) at both 1.5 T and 3 T and is seen to resonate at 3.5 ppm chemical shift (right of the choline peak).
Myo-inositol is a precursor of both phosphatidylinositol (the major inositol-containing phospholipid) and phosphatidylinos...
Article
Susceptibility weighted imaging
Susceptibility weighted imaging (SWI) is an MRI sequence that is particularly sensitive to compounds which distort the local magnetic field and as such make it useful in detecting blood products, calcium, etc.
Physics
SWI is a 3D high-spatial-resolution fully velocity corrected gradient-echo M...
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