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Radiopharmaceuticals II and perfusion of "cellularity"

Thallium 201 chloride (201Tl)

The 201 Tl, radioactive isotope of thallium (Tl 81, atomic weight 204) per decade electron capture by issuing three types of X-rays with half-life of 73 hours and is a cation with chemical properties similar to those of k +. In fact, such as K +, has a predominantly intracellular distribution and its transport within the cytoplasm requires the presence of cell membrane integrity. The mechanisms of intracellular transport are different, some of which are probably not yet clear:

• pump sodium-potassium ATP dependent
• system cotransport of potassium / sodium / chloride
• transport through the channels Ca + + dependent

for these reasons, the 201Tl, tends to accumulate in tissues with high cellularity and cell viability, E 'is negligible in the hyperaccumulator load of necrotic tissue and low level of inflammatory and connective tissue. Other factors which positively affect the accumulation of 201Tl in a tissue is blood flow (its distribution in the context of a body is directly proportional to regional blood flow), the increased vascular permeability and cell membrane.
The heart, liver, spleen, muscles, thyroid, salivary glands and kidneys are normal sites of accumulation of 201Tl. The 201Tl is currently being used since the 70s to study myocardial perfusion in the assessment of ischemic heart disease. With regard to its use in cancer early studies have been performed for the differential diagnosis of thyroid nodules. Later it was used in the diagnosis of various cancers, including those of the parathyroid glands and brain. The disadvantages of 201Tl
reside primarily in the physical characteristics of this radionuclide:

• long half-life involving high dosimetry and the consequent need to use the amount of dose contained causing a signal with low photon flux.
• 72Kev the low energy emission is due to a low resolution image