MRI of the body

Proton Density weighted MRI

Gives best display of adjacent tissues with different proton concentrations, but gives poor discrimination between soft tissue organs.
Different brain diseases could be diagnosed using MRI including lesions, tumours & metastases, infraction, infection.

White matter of the brain has a lower water content than the grey matter and hence appear darker.
Cerebro-Spinal Fluid in brain ventricles appear dark in the brain as its T1 is long and the imaging discriminates against substances with T1 in this range.
A Lesion causes a high signal intensity.

Arrow 'A' indicates an error of lesion, characterised by high signal intensity, attributable to a high water content.

Arrow B indicates an area of white matter.

Arrow C indicates an area of grey matter.

Arrow D indicates an area of Cerebro-spinal fluid (CSF).

Unfortunately, in Proton Density weighted MRI of the abdomen, the organs to not show up clearly, but the technique is still useful in assessing the extent of fluid-filled organs and cavities. It is also useful in demonstration of the vertebral bodies, intervertebral discs and spinal canal.

Signal lost from tissues with a short T2.
CSF appears with higher relative intensity as it has a longer T2.
Lesion maintains high intensity due to the elevated relative T2.
The figure on the right hand side indicates a T2-weighted image of a patient with Progressive Multifocal Leukoencephalopathy (PML), showing a lesion (see arrow) that shows up as a high intensity region due to increased T2 Value.

Tissues with long T1 values appear with a lower signal intensity.
Hence, a lesion and the CSF (long T1s) appears with low signal intensity and is dark on the MRI image.

While MRI is substantially used in imaging of the brain, its use is also valuable in other parts of the body. It could, for instance, in the lung.
Air-filled lungs appear dark due to its low water content, with blood appearing as white. Lung tumours could also be diagnosed with its characteristic T1 in the range of 300-400ms.
The diagram on the right hand side indicates an image of a secondary lung tumour, at the top region of the Right Lung (i.e. left hand side of the diagram). The diaphragm appears white in the central regions of both lungs. Air-filled regions appear dark. The right and left ventricles of the heart appears white in the top-centre-right region of the image.

MRI could also be used on heart to diagnose various diseases like heart valve disorders, tumour, atrial myxoma, pericardial effusion, congenital heart abnormalities, fibrosis or scarring of heart muscle and extent of necrosis (tissue death) of heart muscle. Unfortunately, the use of a strong magnetic field means than patients using pacemakers cannot be scanned using MRI.

MRI Image of liver haemosiderosis. Note that the shortening of T1 relaxation time makes the liver appears darker than normal tissues.

In MRI of the liver, fat degeneration or paramagnetic material accumulation causes a shorter T1. In diseases like inflammation, haemosiderosis, haemochromatosis, the T1 value in regions adjacent to the portal tracts becomes longer, making those regions appear larger.
Malignant tumours of the liver also show up with T1 which falls to the 275-400ms range, which unfortunately also overlaps the regions characterised by cirrhosis and hepatic abscesses. Blood-filled tumours have the same T1 values as blood )350-380ms).
Ascites associated with cirrhosis has a protein concentration whose T1 range is 900-1000ms, while malignancy and inflammation related ascites have protein concentration whose T1 ranges between 300 and 600ms.

The Whole Brain Atlas: http://www.med.harvard.edu/AANLIB/home.html
Provides images ranging from the normal brain to those with various brain diseases
3D models of vocal tracks using MRI: http://www.icsl.ucla.edu/~spapl/projects/mripix/mri2.html
Some Cool images from the Speech Processing and Auditory Laboratory at the University California Los Angeles