Timothy McKnight DO

Spring 2014

What am I looking at? Tracer: Tc99m, I131, I123, In111, F18, Xe133 Agent: pertechnetate, sestamibi, MIBG, pentatreotide, FDG, WBC, SC,

DTPA, MAG3 Whole body or small field of view Multiple phases–

3phase bone Renal exam Delayed images for parathyroid, hemangioma, or whole body In111 and I131

exams

Need to understand the physiology of each tracer. Know a few physics properties

Tc99m 140keV gamma emissions (88%) and internal conversion (12%) 6.02 h half-life

F18-FDG 110 min half life

I131 8.02 d half life

Best PIOPED Interpretation assuming a normal ventilation scan?

A – Very low probability

B – Low probability

C – Indeterminate

D - High Probability

SNM modified PIOPED 2011 High Probability of PE (>80%)

>= 2 Large (>75%) V/Q Mismatched Segmental Perfusion Defects 2 moderate defects (25-75%) equal one 1 large defect

Intermediate Everything Else

Very Low Probability of PE (<10%) Stripe Sign (perfused lung between defect and lung surface) DDx:emphysema, PulmHTN,

resolving PE Non-segmental defects Q defect < CXR abnormality Solitary Large pleural effusion(>1/3 pleural cavity) corresponding to apparent Q defect (no

other Q defects) 1-3 small (<25%) segmental defects Solitary Triple Match Defect (V:Q:CXR) in Mid or Upper Lung (divided in rough thirds of

lung height not by segmental anatomy.) >= 2 Matched (V:Q) defects with Nml CXR

PISAPED for Perfusion only with CXR. >= 1 wedge shaped large perfusion defect and no explanation on CXR.(High Prob) Cannot determine PE+ or PE- Normal 2008 Sostman et al. PISAPED vs mod PIOPED roughly equivalent outcomes

Stripe Sign

Tc99m DTPA aerosol and 1-4mCi Tc99m MAA

Key Finding

Single large V/Q match in Superior segment of RLL

Perfusion defect is equal in size to radiographic abnormality

You must always ask for the CXR

You must be familiar with modified PIOPED II criteria.

Be ready for either Tc99m aerosol(this case) or Xe133 gas vent images!

Tc99m-MAA

Avg 10-30microns

200k-600k particles(3-5mCi)

Lower does in children, pregnancy, R-L shunts (100-200K) usually require 100k for Dx exam

Vent

10-20mCi of Xe133

30mCi DTPA in 2cc nebulizer only 1-2mCi reaches patient.

Let’s Review

Which of the following are not in the differential?

A- Thyroid adenoma

B- Parathyroid adenoma

C- Parathyroid hyperplasia

D- Medullary thyroid CA

E –All of the above are in the differential.

20mCi Tc99m-Sesatimibi Key Findings:

Focal activity just below left thyroid lobe on initial and delayed Tc99m sestamibi images

SPECT images show more specific location of sestamibi activity to facilitate planning of surgical removal

DDX: PTH adenoma, Thyroid adenoma, Met lymph node, Thyroid CA

Primary Hyperparathyroidism 80-85% single or multiple parathyroid adenomas 12-15% parathyroid hyperplasia 1-3% parathyroid carcinoma

~15% of parathyroid adenomas are ectopic

Tc99m sestamibi – mitochondrial localization. Uptake in parathyroid, thyroid, salivary, cardiac, hepatobiliary, bowel, renal tissues Utility of sestamibi is based on earlier washout of thyroid activity

compared with parathyroid adenomas Thyroid adenomas and parathyroid hyperplasia typically are more

intense than normal thyroid on initial images but usually washout by delayed images but occasionally may retain acitivty greater than washed out thyroid background

Tc99m pertechnetate images can be subtracted from sestamibi images to increase sensitivity. If a nodule has increased activity on both sestamibi and pertechnetate this is usually a follicular thyroid adenoma.

Sestamibi is a nonspecific tumor localization agent and may show increased activity in metastatic lymph nodes from: Thyroid carcinoma Breast Cancer Head/Neck Carcinomas

ECTOPIC PARATHYROID ADENOMA

Best Diagnosis? A – Breast CA Mets

B – Paget’s Dz

C – Myelofibrosis

D – Renal Osteodystrophy

E – Hypertrophic Pulmonary Osteoarthropathy (HPOA)

Tc99m MDP / HDP

Key Finding- SUPERSCAN Intense activity throughout skeleton / Minimal or no

perceivable renal activity

DDx

Mets – prostate, lung, breast, lymphoma

Look for patchy distribution and focal distant extremity mets

Metabolic – Renal Osteodystrophy, hyperthyroidism, osteomalacia

Look for uniform distribution, pseduofractures, bowed femurs, prominent costochondral junction activity, disproportionately intense calvarium

Myeloproliferative Dz / Marrow Dz

Lymphoma, myelofibrosis, mastocystosis, leukemia

Uniform Axial and Appendicular activity

Prostate Mets

Renal Osteodystrophy

Best Diagnosis?

A – Brain Death

B – NPH

C – Alzheimer’s

D – Acute Seizure

E – Obstructed VP shunt

500 microcuries In111-DTPA injected by LP

Clinical triad of Wet (incontinence), Wobbly (abnormal gait), Wacky (altered mentation)

Initial images at 2-4 hours and 24 hours post-injection

Normal activity in basal cisterns by 2-4 hours

Activity climbs up over convexities by 24 hours

Activity clears basal cisterns and fills interhemisphereic fissuse, sylvian fissures

Transient reflux in ventricles may occur at 4 hours but should clear at 24 hours

Ventricular activity at 24 hours indicates NPH

Clear ventricles but failure of activity to ascend over ventricles should prompt 48-72hr images.

Best Diagnosis? A –Parathyroid Adenoma

B – Left Colloid Cyst

C – Prior Left Thyroid Lobectomy

D – Right Autonomously Function Nodule

E – Left Thyroid Cancer

Tc99m Pertechnetate scan / I-123 uptakes

Key findings: decreased thyroid uptake / right thyroid lobe nodule with increased activity.

Autonomously functioning nodule results in suppression of normal background thyroid activity by secreting large amounts of thyroid hormone and suppressing the pituitary axis.

More common in younger adults

50% of hyperfunctioning adenomas are autonomously functioning

Tx: I-131 therapy , Surgical excision, Surveillance

Very low risk of cancer (<1%).

2hr 24hr

Increased activity on Tc99m Pertechnetate Thyroid scan

Preserved trapping consistent with solid thyroid nodule

Decreased activity on I-123 scan

Reduced organification

Treat this as a COLD nodule

DDx

Thyroid cancer

Follicular adenoma

Follicular hyperplasia

Nearly all >99% of hot nodules on I-123 are hyperfunctioning benign adenomas and do not requiring further imaging workup

Hot nodule on Tc99m pertechnetate scans require that an I-123 scan be obtained to exclude a discordant nodules which have an increased risk of carcinoma

Discordant nodule should be Biopsied!

Remember only 10-20% of cold nodules represent cancer.

Tc99m TcO4-

I-123

Which of the following is true about this scan? A- This is for preoperative initial

staging

B – Normal scan

C – Findings are suspicious for distant metastasis

D – Findings are suspicious for local recurrence in the neck

E – C and D

Bronchial Atresia

5 years previous

1-5mCi

Many preferring a range of 1–2 mCi

Decreased stunning- decreased uptake of the therapy dose of I131 by residual functioning thyroid tissue or tumor due to cell death or dysfunction caused by the activity administered for diagnostic imaging

Normal Biodistribution: salivary glands, stomach, kidneys, and bowel.

Used to diagnose and treat metastatic thyroid cancer

Used to treat hyperthyroid Multinodular goiter/Graves Typically do pre-ablation scan, post-ablation scan 4-10days post treatment. Then f/u scans at 6 and 12 months post treatment and then intermittently either yearly or every 3-5 years depending on recurrence risk.

Beta-emissions (606keV) treat disease (travel 0.8mm)

Gamma emissions (364keV) are used for imaging.

Half life 8.02 days

Locoregional disease

Single dose of I-131: ~ 65% effective in eradicating disease

Distant metastatic disease

Single dose of I-131

33% effective for lung metastases

7% effective for bone metastases

Star Artifact from septal penetration caused by intense activity in thyroid tissue. Common on initial post-TX scan. Abnormal on follow-ups.

Locally Recurrent Thyroid Cancer Total Thyroidectomy 4 years ago

Initial Post-Tx Scan w/ Star Artifact

Best Diagnosis?

A - Loosening

B - Infection

C - Pagets

D - Stress Fracture

E - Metastasis

Three phase bone scan (20 mCi) Differentiating loosening from infection in a painful joint

w/ arthroplasty is difficult. A normal scan has a high negative predictive value. A positive scan is nonspecific

Typically loosening has focal increased activity on delays at the bone/prosthesis interface especially at the tips of prosthesis stems and variable on dynamic and blood pool phases. Infection is often more diffuse and abnormal on all three phases.

Sulfur colloid combined with indium WBC scans may be helpful. Normal postsurgical activity persists for several months

20% persist up to 1 yr Aspiration and Culture is often necessary.

In111 WBC and Tc99m SC Key findings: Non-spatially congruent

activity around left knee joint. (increased areas on In111WBC that are decreased on Tc99m sulfur colloid)

DDX: Infection Loosening

Post op infections 6mo(1/3), <=1yr(1/3), >1yr (1/3)

Normal postoperative activity on Bone Scan: Hip – up to 1 yr, some minimal activity in

acetabulum, greater trochanter and at fem tip up to 2 yrs but uncommon

Knee-variable, but tends to be less than normal bone activity after first 2 yrs. Any intense activity is suspicious

Infection

Loosening

In111 WBC Tc99m SC

Best Diagnosis?

A – Pagets

B – Neoplasm

C – Stress Fracture

D – Osteomyelitis

E – Fibrous Dysplasia

Focal Bone Lesion

Key findings on Bone scan. Right knee expansile lesion from femoral epiphysis to distal femoral shaft.

Secondary involvment at right shoulder/axilla.

Stepoff suggesting pathologic fracture. Leukemia/Lymphoma

Ewing Sarcoma

Metastasis

Osteosarcoma

Infection

Plain film and cross secitonal imaging necessary in real life but not be provided at boards.

Differential is more important than final diagnosis in this case.

Don’t forget to address if there are skip lesions if you are included osteosarcoma in your differential!

1 yr prior

4 Hours 24 Hours

Type of Scan, Differential and Diagnosis?

In -111 Octreoscan (pentatreotide) Octreotide analog binding select somatostatin receptors

Biodistribution Liver, Spleen(intense), Kidneys/bladder(intense), gallbladder,

blood pool, faint thyroid,

Main route of excretion: Kidneys/Bladder

Neuroendocrine tumors ( carcinoid, panc neuroendocrine, pheochromocytoma, medullary thyroid CA)

Also: pituitary adenoma, meningioma, and others

In 111-Octreoscan with incidental activity in a large goiter.

DDX: Medullar Thyroid CA or Metastatic Disease

No other evidence of cancer. Patient was being w/u for insulinoma which was never found.

Stable US over next 1 year. Biopsy is appropriate given differential.

Many different thyroid pathologies have been reported as false positive on Octreoscan. The most important to r/o is medullary thyroid cancer.

Things other than malignant neuroendocrine tumors can be postive on Octreoscan.

Meningioma, Pituitary adenoma, Goiter, Astrocytoma, Lymphoma, Breast Cancer, small cell Lung CA, Paraganglioma

Type of Scan, Differential and Diagnosis?

PET-CT

Malignant GIST, Pheochromocytoma/Paraganglioma, Pulmonary Chondroma

I123-MIBG Focal increased activity in right adrenal mass (Malignant Pheochromocytoma)

PET-CT Hypermetabolic right adrenal mass (Pheochromocytoma) Multiple hypermetabolic liver lesions (Metastatic GIST) Right parahilar partially calcified mass (chondroma) – no activity on PET (not

shown)

I-131 or I-123 MIBG (meta-iodo-benzyl-guanidine) Guanethdine analog similar to Norepinephrine Pheochromocytomas ( MEN 2A/2B, NF, VHL, Carney, Familial) 90% sensitive Neuroblastoma 90% sensitive Lower sensitivity w/ Carcinoid, Medullary thyroid cancer, Paraganglioma Imaging at 24, 48, 72 hours Biodistribution

Typical: salivary, liver, faint cardiac, thyroid,renal/bladder Rarely: faint nasal, neck muscle, or diffuse lung activity.

Main route of excretion is kidney/bladder

Type of Scan, Differential (Best 3) and Diagnosis? Would you biopsy this?

F18- FDG PET-CT Key finding

Hypermetabolic nodule highly suspicious for Lung CA, no distant mets, lung resection demonstrated adenocarcinoma

ACCP recommends that FDG-PET be used in any for any pulmonary nodule measuring at least >8-10mm that is indeterminate on diagnostic Chest CT and is in a low-to-moderate risk category for lung CA.

DDx for SPN is vast but a few to put in your list of common things are Lung CA Inflammatory (sarcoid/rheumatoid) Infection(granulomas) Hamartoma Carcinoid Met

False-Negatives for PET include: BAC(adenocarcinoma in-situ), carcinoid, mucinous neoplasms

What constitutes a positive PET-CT for SPN is somewhat controversial

Traditional teaching was SUV max <2.5 benign and >=2.5 malignant, no longer favored (too many false negative)

Some report any activity in a nodule above lung background as suspicious. Others use activity equal or greater than mediastinal blood pool as suspicious.

Fletcher et al JNM 2007 study of 532 SPNs

No PET activity (“definitely benign” NPV 97%)

Minimal activity SUV >0.6-0.8 but <1.5-2.0 (“probably benign” NPV 87%)

Activity greater than lung background but less than blood pool.

Activity similar to mediastinal blood pool >1.5-2.0 but <2.5 (“indeterminate” NPV 78%)

F18-FDG PET

Key Finding

Classic locations of symmetric bilateral supraclavicular and paraspinal increased metabolic activity. Does no conform to any abnormality on CT only nml appearing fat

Other common areas or intercostal, perinephric and mediastinum

SUV values are highly variable

Related to adrenergic stimulation of brown adipose tissue for heat production

Winter-months or cold air-conditioned room

Pretreat with benzodiazipines or propranolol

Type of Scan, Differential and Diagnosis?

Tc99m Mebrofenin (Choletec) Key findings: Photopenic area in Right hepatic lobe.

Hyperechoic mass on US. Heteogenous mass on CT. Delayed GB filling by 120 minutes.

Normal gallbladder filling and biliary to bowel transit by 60 minutes.

Nearly all hepatic masses will be cold on hepatobiliary scan.

If no GB filling by 60 minutes can give morphine, otherwise may need delayed images up to 4hrs to exclude cystic duct obstruction.

Delayed biliary to bowel transit very nonspecific. Nml, spinchter of oddi dysfunction/spasm, common duct obstruction (stone, scar, tumor).

Acute Cystic Duct Obstruction

24 yo male with RUQ pain and jaundice

Key findings

Persistent hepatic activity to 24 hours

No biliary excretion

Persistent Cardiac activity

High specific for hepatocellular dysfunction / decreased uptake

Identify what type of radiotracer/exam

Know Tc99m properties in detail

Remember nuclear medicine is more about physiology than anatomy

Don’t forget SPECT

Thank you and Good Luck!