Endocrine System (RP and Diagnosis)

why is I-131 more damaging than the other RPs?

it decays by beta emission

what is the half life of I-131?

8 days

what are the energies of I-131?

- 284 keV

- 364 keV

- 637 keV

what energy do we use, when using I-131?

364 keV

what are the advantages of I-131?

- low cost

- readily available

what are the disadvantages of I-131?

- long half life

- beta emission

- high radiation dose

- high energy

what does I-123 decay by?

electron capture

what is the energy of I-123?

159 keV

what are the advantages of I-123?

- ideal imaging energy

- allows for 80% gamma camera efficiency

- short half life

what are the disadvantages of I-123?

- high cost

- cyclotron produced

Iodine naturally accumulates in thyroid follicular cells by _______ then oxidized and bound to thyroglobulin (Organification) and synthesized as thyroid hormones

active transport (trapping)

Iodine naturally accumulates in thyroid follicular cells by active transport (trapping) then oxidized and bound to _________ and synthesized as thyroid hormones

thyroglobulin (Organification)

what is Tc-99m PERTECHNETATE energy?

140 keV

what is Tc-99m PERTECHNETATE half life?

6 hours

Tc naturally goes to the _____ and gets trapped

thyroid

what does NOT go through the process of making thyroid hormones?

Tc-99m

what are the advantages for Tc-99m?

-Low cost

-Readily available

-Low radiation dose to patient

-Ideal energy

what are the disadvantages for Tc-99m?

Can NOT be used for an uptake

what does F-18 FDG decay by?

Positron Emission

what is the half life of F-18?

110 minutes

what is F-18 used for?

Ideal imaging energy for PET evaluation

Widely used in patients with neoplasms for the determination of disease extent, evaluation of response to therapy and evaluation post therapy

18F- FDG

Recommended as a diagnostic imaging tool in patients with proven thyroid carcinoma who present with elevated serum thyroglobulin and negative whole-body iodine-131 scan results

18F- FDG

The degree of uptake in metastatic thyroid carcinoma has prognostic significance

18F- FDG

Increased anaerobic glucose metabolism, indicated by increased uptake, presents a more aggressive tumor and poor prognosis

18F- FDG

The amount of iodine that is taken in by the thyroid is related to

how the thyroid is functioning

Higher uptake =

more active thyroid function

Contraindications for a thyroid scan?

-Pregnancy/breast feeding

-Recent study containing iodinated contrast (wait min. of 3 weeks)

-Taken thyroid hormones and antithyroid medications

Patient Prep for Uptake?

-NPO after midnight

-Off all thyroid medications

-Low iodine diet for a few days

why do they need to be NPO before uptake test?

Ensures proper digestion & uptake into the thyroid

why do they need to be Off all thyroid medications?

could interfere with the uptake of iodine

why do they need to be on a Low iodine diet for a few days?

Makes sure the thyroid is in an uptake state

uptake dose for I-123?

0.2-0.5mCi or 200-500uCi

uptake dose for I-131?

0.004-0.01 mCi or 4-10uCi

Have patient return ________ after administering RP

4-6 hours or 24 hours later

Count a standard dose in a neck phantom using _____

an uptake probe

Position ______ from the neck phantom

25-30cm

Position the probe _______ from the patient's neck for neck counts

25-30cm

Position the probe _________ above the patient's thigh

25-30cm

why do we use the thigh for background counts?

Thigh/knee has similar size and vascularity as the neck

Normal Ranges for Percent Thyroid Uptake: 4-6 hours

6-18%

Normal Ranges for Percent Thyroid Uptake: 24 hours

10-30%

Factors that decrease thyroid uptake?

-Iodinated contrast media- Iodine overload

-Amiodarone

-Antithyroid medications

-Thyroid hormone replacement

-Failure to respond to TSH

-Insufficient pituitary secretion of TSH

-Thyroiditis

Factors that increase thyroid uptake?

-Graves disease

-Toxic adenoma

-Toxic multinodular goiter

dose for thyroid imaging with I-123?

200-500uCi

how is I-123 administered?

orally through liquid or pill

what must be opened under a fume hood due to the iodine cloud given off?

liquid form of I-123

Advantages for using I-123 in thyroid imaging?

-good imaging energy

-low radiation dose to patient

Disadvantages for using I-123 in thyroid imaging?

-high cost

-not readily available

why do you have to have a wait time when using I-123 for thyroid imaging?

Needs time to acquire in the thyroid

dose for thyroid imaging with Tc-99m?

5-10mCi

how is Tc-99m administered?

IV injection

when does imaging begin after injection of Tc-99m?

20 minutes post injection

Advantages for using Tc-99m in thyroid imaging?

-low radiation dose

-image sooner

-higher doses

-available and abundant

Disadvantages for using Tc-99m in thyroid imaging?

is not organified by the thyroid

what collimators are used in thyroid imaging?

-Pinhole Collimator

-LEAP collimator

Collimator used for High resolution for small organs?

Pinhole Collimator

Collimator used for Bird's Eye view (head, neck and chest)?

LEAP collimator

Indications for thyroid imaging?

-Determine size, shape, function

-Determine if a palpable nodule is functioning

-Locate ectopic thyroid tissue

-Determine if a mass is thyroid tissue

Patient Prep for thyroid imaging?

Same as uptake but not as strict

patient positioning for thyroid imaging?

supine with neck tilted backwards (using towel or pillow)

why do we hyperextend the neck?

Keeps salivary glands from superimposing the thyroid (overshadowing)

what are the four images we take with thyroid imaging?

-anterior with marker

-anterior without marker

-RAO

-LAO

what does a HOT nodule mean?

Functioning nodule

what does a COLD nodule mean?

nonfunctioning nodule

20% more chance of being cancerous

COLD nodule

what is Multinodular?

-Has multiple hot and/or cold spots

-Thyroid is usually enlarged (goiter)

what is a COLD nodule normally?

a cyst or adenoma

what is Ectopic Thyroid Tissue?

Thyroid tissue outside the normal thyroid area

where can Ectopic Thyroid Tissue be located?

the neck, base of tongue, pelvis, chest

May need higher energy to avoid attenuation

Ectopic Thyroid Tissue

what is Thyroiditis?

Inflammation of the thyroid

how is Thyroiditis shown?

course patchy distribution

what is another name for Diffuse Toxic Goiter?

graves disease

how is graves disease shown?

-presents as a uniform increased activity with enlargement

-Often shows the pyramidal lobe

what is graves disease uptake ranges?

40-70% value ranges

what is Thyroid carcinoma?

a growth of abnormal cells (or tumors) that starts in the thyroid

what is graves disease?

an autoimmune disorder that causes the thyroid gland to overproduce hormones

how is Thyroid carcinoma shown?

-Shows hot and/or cold nodules

-Can appear as an extension of a lobe

Scan show more activity within the salivary glands compared to the thyroid is an Indication of

hypothyroidism

An ultrasound proved the thyroid to be inflamed is an Indication of

Thyroiditis

what is Lingual Thyroid?

where thyroid tissue is located at the base of the tongue instead of its normal position in the neck

what is Ectopic Thyroid?

where thyroid tissue is located outside its normal position in the front of the neck

what is Post thyroidectomy?

Patient has thyroid removed due to CA

what is Post radioiodine therapy?

-Patient had Iodine therapy to destroy the thyroid, due to hyperthyroidism

-Looking for residual thyroid tissue

when do we perform Post thyroidectomy?

1-2 months post thyroidectomy

when do we perform Post radioiodine therapy?

Commonly 5-7 days post administration

what is the dose for I-131 whole body scan?

Ingestion of 2-10mCi

how is I-131 administered for a whole body scan?

orally

Patient Prep for I-131 whole body scan?

-Must be off thyroid hormones

-No iodinated contrast

-NPO 4-hours prior to administration and 1-hour post ingestion

Obtain images with a ______ for I-131 whole body scan

high-energy collimator

Normal Hot Spots for I-131 whole body scan?

-Nasopharynx region/Mouth

-Stomach

-Bladder

-Salivary glands

-Colon

-Minimal liver activity

why does liver activity appear in whole body scans?

from metabolism of radioiodine thyroid hormones

Abnormal Hot Spots for I-131 whole body scans?

-residual tissue within the thyroid bed

-Cervical lymph node METS

-Pulmonary METS/diffuse or focal lung uptake

-Skeletal METS

-Other distant metastatic lesions

A post-therapy scan is often more sensitive than a diagnostic iodine scan. why?

because the higher administered activity of 131I can reveal additional sites of disease that were not visible on pre-therapy imaging

for patients to be allowed to be released from the nuclear medicine department following radionuclide therapy?

-No individual member of the public will receive more than 5mSv from the patient

-When measured from 1 meter, the patient does not read more than 0.07mSv/hr using a survey meter

-The administered activity is less than 30mCi

All patients should be instructed __________ on how to reduce unnecessary radiation exposure to their family members/public and how long restrictions last

orally and given written instructions

TI-201 dose for parathyroid imaging?

Administered 2-3mCi via IV

how does TI-201 localize?

Localizes within parathyroid tumors

Peak uptake in the parathyroid with TI-201?

5-10 minutes