Transmits a signal into the body and creates and image from the signal returning from the body after it has interacted with the microenvironment.

No ionizing radiation.

Uses electromagnetic waves in the same proportion of the electromagnetic spectrum as FM radio.

Is also a tomographic imaging modality producing two-dimensional images consisting of individual slices of the body.

Spatial localization is achieved by gradient encoding, the switching on and off of the magnetic field gradients and the source of the loud noises heard during the examination.

The signal is a microwave which excites water protons in the body to higher magnetic energy states.

As water protons relax back to the unexcited state they emit microwaves that are received and interpreted by the scanner, reflecting the magnetic milieu near the protons.

Water molecules have 2 protons which have positive charge and act as small magnets on a subatomic scale.

The body positioned within the large magnetic field of an MR scanner, which is typically 30-60 thousand times stronger than the magnetic field of the earth, produces collective magnetization that can be measured out of the body and generates high resolution images.

Protons in a magnetic field absorb energy at a specific frequency and then re-emit the energy at the same frequency.

Breast imaging has a high sensitivity for breast cancer detection, reported as high as 94-100%, but a lower specificity, reported as 37-97%.

Breast imaging can revel additional lesions not visible on the mammogram between 27-37% of patients.

Breast imaging is twice associated sensitive and three times more specific than mammograms in detecting breast cancers that are radiologically and clinically occult.

MRI twice as sensitive as mammography in detecting malignancies in women with a genetic susceptibility to breast cancer.

Can alter surgical management in breast cancer in 16% of patients.

Breast MRI leads to greater extent of surgical treatment for breast cancer demonstrating upstaging or new findings in 8% of patients who undergo MRI before primary breast cancer treatment (Furman B et al).

Breast MRI has led to wider excisions during breast conservative therapy, alteration in surgical management of the ipsilateral breast from breast conservation to mastectomy, or even the addition of a contralateral mastectomy, and in as many as 13-29% of cases, and this trend is more pronounced in younger women.

Breast MRI in a DCIS patient population triples the rate of mastectomy over those who do not have such a study.

While multiple studies indicate MRI of the breast is more sensitive than mammography in detecting breast cancer it has lower specificity and substantially higher cost, is more invasive, and requires an intravenous injection of contrast material.

Presently there are no randomized trials to determine whether the use of breast MRI decreases breast cancer mortality more then the use of mammography.

Breast MRI use should be limited to patients with increased risk of breast cancer, such as women with genetic mutations, strong family history of breast cancer, or for selected clinical situations.

Low signal intensity on T1 weighted images and high signal intensity on T2 weighted images of the bone marrow suggest an infiltrating process in the marrow.

Contraindications include the presence of cardiac pacemakers, cerebral aneurysm clips, cochlear implants, orbital foreign bodies, recent surgery and severe claustrophobia.

Is the optimal imaging technique for assessment of the bone marrow and differentiation of hematopoietic marrow from nonhematopoietic marrow.

Since most prostate cancer metastases begin within the bone marrow it is more sensitive to its detection than bone scan or CT of the bone.

A magnetic field strength of al least 1.5 Tesla (T) is required for quality studies of the prostate.

The use of an endorectal coil with a pelvic array coil improves quality of images and is recommended for prostate MRI study.

T2-weighted images provides adequate anatomical imaging of the prostate and is essential for detection, localization and staging of prostate cancer.

T-2 weighted images cancer of the prostate demonstrates decreased signal intensity within the high signal intense peripheral zone of the prostate.

In prostate cancer T-2 weighted images may have homogenous low signal intensity within the heterogeneous signal intensity transition zone.

Dynamic contrast-enhanced MRI provides data about tissue vascularity and can demonstrate increased vascular permeability and interstitial fluid volume present in prostate cancer foci.

Has poor sensitivity to detect cortical bone destruction than does CT scan.

Diagnostic modality of choice in patients suspected to have spinal infections.

Imaging modality of choice in the diagnosis of radiculopathy, spinal cord abscesses,

Spinal cord tumors, spinal stenosis and spinal vascular lesions.

Imaging pelvimetry accurate in bony measurement with a 1% variation rate versus 10% for radiographic pelvimetry.

Can demonstrate bone erosions 1 year earlier than conventional radiography in the evaluation of rheumatoid arthritis.

Iron deposits in tissues act like small magnets when placed in a strong magnetic field causing proton diffusion along different paths with different magnetic profiles, disrupting coherence among the protons and darkening the image.

Proton MR spectroscopic imaging (MRSI) for the prostate provides information about metabolites in the prostate with a spatial resolution of 0.24-.07 cm3.

Nephrogenic systemic fibrosis may be associated with gadolinium contrast agents utilized in MRI enhancements.

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