Thyroid test out

Endocrine function?

function: synthesis, storage, and secretion of hormones that regulate biochemical and metabolic processes throughout the body

What makes a tissue Endocrine?

-produce specific hormones, cause cell to respond predictably

-secrete hormones directly into circulating blood

-need specific receptor molecules/sites on cell

thyroid hormones?

T3 and T4 - secreted by thyroid and regulates tissue metabolism

TSH - pituitary

TRH - hypothalamus

thyroid requires ______ to form T3 and T4

iodide from food and water

hormone feedback loop?

- neurons in the hypothalamus secrete TRH

- which stimulates cells in the

pituitary to secrete TSH

- TSH binds to receptors on the thyroid gland, stimulating synthesis and secretion of T3 and T4

when blood concentrations of T3 and T4 increase above threshold, TRH secreting neurons in the hypothalamus stop secreting TRH until needed again

at the tissue level the free _____ is converted into _____

T4 is converted into T3

- T3 has a direct effect on cellular metabolism

what does thyroid hormone synthesis depends on....

the trapping and organification of iodine in food and water

why is iodine important to the thyroid

it is the only organ that can organify and trap iodine

what joins each lobe of the thyroid together

the 2 lobes of tissue are joined by the isthmus

location of thyroid

in front of trachea below thyroid cartilage

how much does thyroid weigh?

15-25 g

how does the thyroid develop as we grow in an embryo

starts at the base of the tongue and migrates downward to the neck/thyroid cartilage

sometimes there are remnants of tissue in the path or you can have a lingual thyroid at the base of the tongue

When is thyroid able to concentrate iodine in a fetus?

By week 8

what happens during fetal development if the thyroid gland is congenitally absent or fails to function?

child is at risk to become cretin

- infantile/juvenile result of severe hypothyroidism and produces a dwarfed child

- need thyroid replacement hormone for life

RPx method of localization?

all are ACTIVE TRANSPORT

Iodines - trapped and organified

TcO4- is only trapped

I-123

- 13.2 hrs

- decays by electron capture

- 159 kev

- use pinhole collimator

best one

RPx dose for iodine uptake scan

4-15 uCi of I-131 (not used)

200-400 uCi I-123

ORALLY

I-131:

half life

kev

used for

- 8.1 days t1/2

- 364 kev

- beta emitter

- used for therapies only

- hyperthyroidism, thyroid remnant ablation, thyroid cancer treatment

I-131 whole body imaging dose

2-5 mCi

dose of I-131 to treat cancer

30-100 mCi to ablate remnants

150-200 mCi to treat local metastases

200-300 for distal metastases

Tc-99m pertechnetate

how is it used to image the thyroid

the pertechnetate enters the intrathyroidal iodine pool however it only traps iodine and does not organify it

washes out at 20 minutes

Pertechnetate dose

5-10 mCi via IV

When is Pertechnetate used?

When iodine is contraindicated

-chronic thyroiditis has better uptake with pertechnetate

-when Pt has recieved thyroid blockers

-study needs to be done in less than 2 hours

Clinical indications

hyperthyroidism (overactive)

hypothyroidism (under-active)

thyroid nodule

enlarged thyroid

palpable nodule

thyroid carcinoma

hyperthyroidism symptoms?

- increased appetite

- weight loss

- can't sleep

- fatigue

- muscle weakness

- GI disturbances (increased bowel frequency and diarrhea)

- warm heat intolerance

- sweating

- tremors

- rapid heart rate

- palpitations

- emotional outburst

what does T3 and T4 looks like in HYPERthyroid pts vs. HYPOthyroid

Hyper:

INCREASED T3 & T4 levels

suppressed TSH

hypo:

DECREASED T3 & T4

INCREASED TSH

hyperthyroidism?

what does T3 or T4 look like?

increase in metabolism

too much, overactive

thyroidtoxicosis

T3 2-3x increased

increased T3/T4 ratio

what antithyroid medications are used for the pharmacological block at the organification step of iodine metabolism for hyperthyroid therapy?

sulfonylureas methimazole (Tapazole)

and Propylthiouracil

Hyperthroidism:

Grave's Disease

Plummers disease

toxic multinodular goiter

Grave's: overactive gland - thyroid is the source of excessive thyroid hormone - homogenous function

Plummer's: hyperactive adenomas

Toxic multi nodular goiter: hyperactive multi-nodular regions

- solitary hot nodules or multi-nodules

-hyperthyroidism is secondary to overproduction of thyroid hormone due to nodule/s

- focal areas of increased/decreased function

Grave's Disease

WHAT CAUSES IT?

- leading cause of hyperthyroidism

-autoimmune system

- production of immunoglobulins which attack thyroid

- antibodies bind to TSH and stimulate the release T3/T4

OVERPRODUCTION

WHO IS AT RISK FOR Grave's disease

30-40 y/o females

Grave's disease image looks like...

what do the hormones look like?

homogeneous increased uptake

increased t4/t3

supressed TSH

low TRH stimulation

Toxic Nodular Goiter (Plummer's Disease)

- caused by autononomous function of one or more thyroid adenomas producing hyperthyroidism

- nodules suppress the rest of the gland

what test do we do if we suspect toxic nodular goiter or Plummer's?

TSH supression test

- only the nodule will show up until TSH is given

TNG/plummers is mostly seen in...

usually seen in 40-50 yo

females more common

TNG/Plummer's image looks like?

hormones look like?

- focal hot spots with little or no gland appearing

- administer TSH, suppressed areas will appear

- increase T3 and T4

- suppressed TSH and TRH

I-131 dose for TNG/plummer's

high dose because of resistance

what is Hashimoto's?

who does it effect?

what do pts present with?

- autoimmune disorder

- mostly females

- 85% of thyroiditis is hashimoto's

- large firm rubbery gland

- hyperthyroidism, euthyroid state, hypothyroidism

Hashimoto's image?

coarse patchy image

Hypothyroidism?

caused by thyroid hormone deficiency or failure for thyroid to synthesize and release the thyroid hormone

"primary hypothyroidism"

Hypothyroidism symptoms

- cold intolerance

- dry pale skin

- decreased appetite

- weakness

- hair loss

- weight gain

- low BP

- heart failure

- heart enlargement

- depression

- sluggishness

- constipation

secondary hypothyroidism?

thyroid is intact but TSH is insufficient - pituitary problem

causes of hypothyroidism?

Hashimoto's

- viral diseases (DeQuervains)

hormones in hypothyroids?

decreased t3 and t4 and increased TSH

thyroid nodule can be caused by?

overproduction or underproduction fo thyroid hormone

types of thyroid cancer?

papillary carcinoma (2/3) - spread through lymphatics to regional or mediastinal lymph or lungs

follicular carcinoma (1/3) - spread vascular to distal sites

risk factor for thyroid cancer

age

sex

size of primary tumor

histopathological findings

metastases

lymph involvement

thyroid cancer is hot or cold?

cold - malignant tissue has less iodine trapping and function

advantages of Tc-99m pertechnetate

140 kev is more efficiently detected than 364 kev by I-131

cheap (2-10 mCi)

short half life - low dose to pt

better image quality

accessible

if you have hot spot of TcO4- with a cold spot on Iodine image it may be ______

cancerous

cold on Tc with be cold with iodine

images with Tc-99m pertechnetate start when?

15-20 post inj

trapped not organified

trapped poorly in cancer = cold spot

not used for metastatic thyroid cancer - short physical and biological half life and doesn't get trapped well in thyroid cancer tissue

F-18 FDG

see thyroid cancer in pt who have elevated serum thyroglobulin and negative whole body I-131 scan results

Thyroid Iodine Uptake test indications

- assess function and structure of gland

- correlate palpable mass with scintigraphy

- locate ectopic thyroid

- evaluate neck or substernal mass

- differentiate pathologic disease states

subacute thyroiditis looks like

- symptoms of hyperthyroidism

- elevated T3 and T4

- suppression of TSH

- low iodine uptake

Patient prep for uptake scan?

- NO interferring medications (thyroid hormone, anti-thyroid medication, vitamins, supplements)

- No thyroid meds for 4 weeks

- NO x-ray studies with iodine contrast for 6 weeks

- NO pregnant or nursing

- NO recent nuc med procedures

- NPO 2-4 hrs before test and 2 hours after

- get labs for thyroid hormones in blood

UPTAKE SCAN protocol

- pt is seated or lying down with neck extended

- probe with flat field collimator

- counting done at 2-6 hr or 18-24 hrs after administration of RPx - 1 minute counts using thyroid probe

- NO MORE THAN 20 to 30 cm away

- then acquire 1 min counts of pt thigh at same distance

- get 1 minutes of counts using a standard in thyroid phantom at same distance (done before pt)

- acquire 1 minute of background counts for the room (sone before pt)

uptake equation

neck counts- thigh counts / standard counts- bkg X 100

normal uptake %

24 hr 10-35%

4-6 hr 5-18%

factors affecting uptake?

- oral contraceptives

- pregnancy

- thyroid meds

- contrast media'

- kelp

- cabbage, turnips

- seafood

- antihistamines and decongestants

- cough syrups with I

- corticosteroids

- renal failure

- chronic liver disease

thyroid probe

sodium iodide crystal with open-face collimation

Thyroid imaging Scan I-123 or TcO4- Indications

-size and shape of thyroid tissue

- abnormal labs

- eval for hyper/hypothyroid

- evaluation of nodules function

- evaluate neck mass

thyroid imaging uses what collimator

pinhole collimator or LEHR (low energry high resolution)

pinhole collimators do what to the image

invert and reverse

- use marker

- the closer the hole the more magnified

Thyroid imaging uses what RPx

pertechnetate

I-123

Thyroid imaging using Tc-99m pertechnetate

imaging times with I-123

- starts 15-20 min post inj

- 2-10 mCi inj via IV

- 2-6 hr or 24 hrs or both

how can you tell the size of the thyroid?

- take image using a marker

- ruler marker with Co-57 and lead

Thyroid imaging using I-123?

- images taken 2-4 and 20-24 hrs after admin

- 200-400 uCi

- pt neck is hyperextended

- 10 minute pictures in ANT, RAO 45, LAO 45

- ANT marker picture on supersternal notch

Thyroid imaging scan using tc-99m or I-123

- collimator?

- kev?

- views?

- doses?

- use gamma camera with pinhole or parallel-hole collimator or LEHR

- tc-99m 140 kev or 159 kev I-123

- ANT, RAO, LAO

- 200-400 uCi I-123 orally or 2-10 mCi Tc-99m IV

Thyroid imaging scan using tc-99m or I-123 patient prep?

- thyroid hormone medication

- antithyroid medication

- vitamins?

- supplements?

- recent x-ray studies w contrast

- pregnant or nursing

- recent nuc med procedures

patient should be NPO for

4 hours befrre admin and 1-2 hours post admin

Thyroid imaging scan using tc-99m or I-123 PROTOCOL?

- I-123 imaging is at 4 hr or 18-24 hr or BOTH

- Tc imaging starts 15-20 mins post inj

- pt supine with neck extended

- pinhole collimator with whole thyroid in FOV

- tc: 100-200,000 counts of 5 mins acquisition

- I-123: 50-100,000 or 10 minute acquisition

- Views ANT, RAO, LAO, ANT w marker

ABNORMAL SCANS with no visualization of thyroid could be from

- elevated iodine pool (contrast studies, iodine medications)

- eating cabbage or turnips

- antithyroid drugs like propylthiouracil

- thyroiditis

- hypothyroidism

-ectopic thyroid

whole body imaging pt preparation

- low iodine diet 1-2 weeks prior

- avoid iodine contrast 4-6 weeks prior

- withdrawing thyroid replacement therapy

why do whole body imaging?

look for remnant functioning thyroid tissue after surgery or ablation

WB scan collimators?

high energy all purpose for I-131

low energy all purpose I-123

dose for whole body?

I-131 1-5 mCi

I-123 2-5 mCi

orally

whole body scan pt prep?

- thyroid hormone replacement should be withheld to render the pt to hypothyroid (thyroid simulanting hormone >30 mU/L) OR thyrogen should be given

- Low iodine diet is followed 2 weeks prior

- NPO 4 hours before

Whole body imaging protocol I-131 routine WB?

dose:1-5 mCi

- imaging begins 48-96 hr after admin

- images of neck and WB

Whole body imaging protocol I-131 post ablation?

images begins 5-7 days after ablation

images of neck and WB

Whole body imaging protocol I-123?

- images 18-24 hours after RPx

- pinhole images of thyroid bed and WB

- SPECT/CT

clinical indications for thyroid ablation?

Grave's or plummers - 30 mCi

cancer - 100 mCi

ablation contraindications?

pregnancy

breast feeding

severe thyroidtoxicity

prior to I-131 treatment of hyperthyroidism every pt must have?

women must have?

- a thyroid uptake scan done

- women need pregnancy test within 5 days

How do we avoid thyroid storm?

- the release of stored thyroid hormone into circulation

- treat with beta blockers

3 things for pt to be release after therapy

1. no member of the public will recieve more than 5 mSv from the pt

2. when measured at 1 m the pt does not read more than 0.07 mSv/hr

3. administration dose is less than 30 mCi

every therapy pt should be given?

written instructions on what to do and how to limit exposure

- sleeping arrangements, avoid pregnant ppl, avoid children or infants, no public transportation, driving arrangements

- saliva and sweat is radioactive

- use disposable utensils and dishes

- flush toliet twice

- shower often

- isolate from others

- stay away from pets

inpatient considerations for therapy pts

- notify nurses and care takes

- isolated room in corner

- wrap room in absorbent paper

- no visitors

-

multiple warm/hot nodules among cold nodules may be seen in...

Hashimotos thyroiditis OR multi nodular goiter

Diffusely enlarged, homogeneously increased uptake is......

Grave's disease

calculating dose equation for hyperthyroidism?

thyroid mass (g) X 80-200 uCi/g

divided ///////

percent uptake at 24 hrs

solitary and multinodular goiters are __________ to radioiodine

radio resistant

pt can leave hospital after reading is ......

< 5 mR/hr

RPx and dose for parathyroid imaging?

tc-99m mibi 20-30 mCi

clinical indications for parathyroid imaging?

localization of parathyroid adenomas

collimators for parathyroid imaging?

low energy high res

patient positioning and acquisition times for parathyroid imaging?

pt is supine with head and neck extended

10 minute statics

- include mediastinum and heart on statics

- 10 and 30 minutes post inj

- delays at 2.5 to 2.5 hours post inj

- SPECT/CT for early and delays

why include heart in one of the statics?

look for ectopic tissue

size of parathyroids?

3-4 mm across and weigh 35 mg each

how many parathyroids do you have normally?

4

some people have more 3-6