T1 shortening: fats and oils
Are there other fats and oils that produce a bright T1 signal?
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Note: In this Q&A we adopt the convention that substances "bright" on T1-weighed images have short T1 values. This is true for most (but not all) pulse sequences. For a detailed explanation, click here.
T1-weighted image of a bath oil bead taped as a fiducial marker over the site of a visible skin abnormality.
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In addition to triglycerides and free fatty acids, a few other exogenous oily substances also possess short T1 and appear bright on T1-weighted images. One example commonly seen is the use of a vitamin E capsule, fish oil capsule or bath oil bead as a fiducial marker taped onto the patient. It should be noted that most commercial MR markers contain a dilute paramagnetic solution rather than fats or oils, which has some advantage in that they are still visible on fat-suppressed images.
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Mineral oil and oil emulsions have also been used successfully as positive MR contrast agents for the upper gastrointestinal tract. These agents are reasonably palatable (well, maybe not reasonably), producing a bright intraluminal signal on T1-weighted images. They result in satisfactory opacification of the stomach and proximal small bowel for upper abdominal MR studies. However, they are absorbed in the middle and distal small bowel so are not suitable for jejunal, colon, or pelvic imaging.
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An exogenous oily substance now of primarily historical importance is Pantopaque™ (iophendylate). From the mid 1940's to the 1980's Pantopaque™ was the primary intrathecal contrast agent used for myelography. At the end of the procedure the material was supposed to be removed through the same spinal needle used for injection. Invariably, however, some was left behind, and if so, persists forever! Pantopaque™ has short T1 and short T2 values, meaning it is bright on T1-weighted images and dark on T2-weighted images. Occasionally you may encounter an older patient with intrathecal Pantopaque™ still present.
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Appearance of Pantopaque on T1 weighted imaging and radiography. Its chemical structure is shown. Pantopaque was still used in some centers as late as 1995 but withdrawn from the market due to its association with arachnoiditis.
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References
Braun IF, Malko JA, Davis PC, et al. The behavior of Pantopaque on MR: in vivo and in vitro analyses. AJNR 1986; 7:997-1001
Braun IF, Malko JA, Davis PC, et al. The behavior of Pantopaque on MR: in vivo and in vitro analyses. AJNR 1986; 7:997-1001
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