History:
80 year-old female with sudden onset of loss of vision from left eye.
Patient was referred to Main Street Radiology for brain MRI with
diffusion imaging.
|
|
|
Figure
1 |
 |
|
Figure
2 |
 |
|
Figure
3 |
 |
|
Figure
4 |
Findings:
On the conventional axial T2-weighted image (Figure 1), a focal area
of increased signal is seen within the right coronal radiata (arrow),
which is low signal on the corresponding diffusion weighted image
(Figure 2), compatible with an old infarct. Within the right
occipital lobe, high signal abnormality is seen on both the
T2-weighted and diffusion-weighted images (Figures 3 and 4),
compatible with an acute infarct.
Discussion:
Diffusion is the term used to describe the random, Brownian motion of
water molecules. In diffusion-weighted imaging (DWI), MR images made
sensitive to the diffusion properties of water molecules are
generated. This requires high performance magnetic gradients and was
introduced into clinical practice in the mid 1990's.
Diffusion-weighted MRI provides image contrast that is different from
that provided by conventional MR techniques. Application of diffusion
imaging has been found in ischemia, tumors, infection and white matter
disorders.
The most important and widely used
clinical application of DWI is in the evaluation of ischemia. DWI is
the most sensitive method for detection of acute ischemia, allows
distinction of old versus new infarct, and helps distinguish acute
ischemia from other processes with a similar conventional MR imaging
appearance. DWI in conjunction with perfusion imaging can also be used
to determine viable ischemic tissue versus non-viable infarcted
tissue. On DWI, an infarct can be detected within minutes of onset of
clinical symptoms, several hours before conventional MR imaging. The
diffusion properties of infarcted tissue follow a predictable course-
they are virtually always abnormal in the first 24 hours and virtually
always normal 2 weeks later.
Restricted diffusion can be seen in
processes other than acute ischemia. Brain abscesses have been shown
to have restricted diffusion possibly secondary to the viscosity of
pus. DWI can also be used to differentiate arachnoid cysts from
epidermoid cysts. Cytotoxic edema (e.g. ischemia) can be easily
distinguished from vasogenic edema ( e.g. posterior reversible
encephalopathy syndrome). Increased diffusion is also seen in acute
demyelinating plaques. Diffusion tensor imaging is currently being
developed to study white matter tracts and shows great promise.
DWI is available at Main Street
Radiology, utilizing our high field magnet and high performance
gradients. When ordering a brain MRI, DWI can be requested by the
referring physician at no extra charge and only adds minutes to the
exam.
|
Main
Street Radiology
MRI
Clinical
Case Studies |
|
|
