Methods of imaging
1).Asking the disease history and palpating the thyroid of patients before the examination.
2). Administration of radiopharmaceuticals(or imaging agents)
can obtain the image of thyroid(site,morphology,size,function).
r
r
r
131I or
99mTc
r
Trapped by thyroid
Principle of dynamic thyroid imaging
• iv administration imging agent( 99mTcO4-)
metastasis of thyroid carcinoma ❖ The scanning must be performed at least 24h after oral 131I
Iodine-123(123I): ➢ It decays by electron capture with a r-photon (energy is
The second part
Imaging agents and their futrers, imaging methods
Imaging agents and their characteristics
Iodine-131(131I):
❖ Long physical half-life(8.04d) ❖ β-rays occupy 90%,r-rays only occupy 10% of its emission ❖ The energy of principal r-ray is high(364 Kev) ❖ A relatively high irradiation dose to the thyroid and whole-body ❖ Easily obtained and with lower cost ❖ Mainly be used for detecting ectopic thyroid tissue and
20-30min
oral
1.85-3.7MBq(5q(2-3mci)
3).The acquisition of images.
159 Kev, which is very suitable for imaging). ➢ Physical half-life is 13.27h ➢ High cost(produced by cyclotron) Technetium –99m(99mTc) ➢ It decays by pure r-rays(energy is 140 Kev) ➢ Short Physical half-life(6.02h) ➢ Easily obtained and lower cost ➢ Lower irradiation dose to the thyroid and whole-body ➢ Disadvantage is its non-specificity
flow with
blood in vein to heart to artery system
to
thyroidal artery
to thyroid
• Detecting the r-ray emitted by radionuclides and acquire the images continually with certain nuclear device. By these images we can obtain the information of thyroid’s bloodflow(speed and amount), reflecting the function of thyroid
The first part
Classification and principle of thyroid imaging
The Classification of thyroid imaging
①Thyroid static imaging
②Thyroid dynamic imaging
Principle of static thyroid imaging
• Administrating an agent(131I-NaI or 99mTcO4- ) which can be trapped and accumulated selectively by thyroid when entering the body of patients.
• Certain time after administration, Detecting the r-ray emitted by radionuclides in the thyroid with certain nuclear device,then we
Thyroid Imaging
Contents
➢Classification and principle of thyroid imaging ➢Imaging agents and their features, imaging methods ➢Normal and abnormal imaging ➢Clinical application of thyroid imaging
Table 1 Comparision of two agents
agents 99mTcO4131I-NaI
the route of administrati on
The dose of agents the time of imaging
iv(as bolus) 185-370MBq(5-10mci) immidiately or