Nuclear Medicine

Cardiac

Agents

ARTIFACTS

Breast attenation = anteroseptal wall (mild to moderate fixed defect)
Diaphragm attenuation = along mid to basal inferior wall (mild to moderate)

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Imaging Agents

Pathology

Stress Agents

Regadenoson - A2A Receptor Agonist, CORONARY VASODILATOR, good for pts w/ LBBB. B/c contractile agents (dobuatamine, exercise stress) means more BPM, so there is a delay in diastole w/ LBBB when you have too much BPM w/ a LBBB, you get less perfusion in diastole, so can get a false positive


Adenosine - A1 receotir agonist = AV block, so CONTRAINDICATIONS are active wheezing, 2nd or 3rd degree blocks, SEVERE asthma or SEVERE COPD, seizure history

Stunned Myocardium = Decreased contractility, normal perfusion, and FDG UPTAKE


Hibernating myocardium = Decreased contractility, decreased perfusion, and +FDG Uptake


Scar = decreased contractility, decreased perfusion, and no FDG uptake. Non-viable tissue

N-13 = Better spatial resolution,r short half life of 10 minutes
Rubidium-82 = Half life of 76 seconds
Thallium-201 = Excellent first pass extraction, half life of 3 days, image 10 minutes after , FOR VIABILITY can image 24 hrs later b/c thallium has good redistribution in the myocardum
Tc-99m Sestamibi or Tetrofosmin = PERFUSION agents, imaged 30-45 minutes after injection to allow for liver clearance.

Pulmonary


Imaging Agents
Xenon = Can't do multiple projections, super short half life, need negative pressure rooms, low photo peak of 81 kev means lots of soft tissue attenuation,


Tc99M-DTPA = Can do multiple projections, better photon flux, less soft tissue attenuation. MUST DO VENTILATION IMAGING BEFORE PERFUSION


DTPA has central accumulation in pt's with ASTHMA or COPD (can see the trachea and stuff, which can then go down the esophagus and into the stomach)


IN-111 WBC = Uptake at 1 hr in lungs is physiologica, uptake after 4 hrs or more delayed could be infections

Immune

Ga-67 = GOOD FOR VERTEBRAL OSTEOMYELITIS
In-111-WBC Scan = Good for ABD infections (Gallium has liver and spleen uptake which obscures the bowel)

Doses
VQ Scan = More dose to fetus
CTPA = More dose to Mom and Mom's breasts

FALSE NEGATIVE FDG PULMONARY MALIGNANCIES
-Well differentiated adenocarcinoma w/ lepidic pattern
-Carcinoid

MODIFIED PIOPED II CRITERIA


High Prob = >2 large matched defects (>75% of a lung segment)
Very low probability = Nonsegmental defects, stripe sign, 1-3 small segmental defects, single triple matched defect in upper lung, perfusion defect smaller than corresponding CXR abnormality


Nondiagnostic = Perfusion does not fit into these categories (common ND is triple matched defect in LOWER LOBES)

Renal

IMAGING AGENTS:
DTPA = GFR (20% of renal plasma flow is cleared by GFR)

  • Good for GFR
    MAG-3 = Tubular secretion (80% of renal plasma flow cleared by tubular secretion)
  • Good for renal flow and function, and if concern for OBSTRUCTION)
    DMSA = Renal cortical imaging agent
    -Good for eval of pyleonephritis, cortical scar, differential renal fxn

Renogram Interpretation of Renal Dysfunction
Normal = Prompt tubular extraction (time to peak 3-5 minutes), Good renal clearance/excretion (time to half peak 6-10 minutes) or a 20 min/peak ratio <0.3


Mild Renal Dysfunction = Normal time to peak (3-5 minutes), delayed 20 min/peak ratio >0.3


Moderate Renal Dysfunction = Delayed time to peak, and delayed 20 min/peak ratio >0.3


Severe Renal Dysfunction = Poor uptake, progressive accumulation and no significant clearance (markedly prolonged time to peak)


LASIX RENOGRAM INTERPRETATION
-Diuretic T 1/2 time of < 10 minutes = Nonobstructive
-Diruetic T 1/2 time of 10-20 minutes = indeterminate
-Diruetic T 1/2 time of >20 minutes = Obstructive

BILATERAL DELAYED CLEARANCE IN CAPTOPRIL STUDY?

  • Bilateral Renal Artery Stenosis is not as common (only 30% in pts older than 55), think of other causes
  • Calcium Channel Blockers, Captopril induced hypotension,, and dehydration

PEDS

Renal Scintigraphy


-Mild VUR = Visualization of the ureters
-Moderate VUR = Visualization of the non-dilated pelvicalcyceal system
-Severe VUR = Visulization of pelvicalyceal system and dilated collecting system


Who gets is? --> Children w/ UTIs, suspected VUR, screening in siblings of pts w/ VUR

STRESS FX ON BONE SCAN = Fusiform shape, focal cortical uptake, 3 phase positive uptake


SHIN SPLINT ON BONE SCAN = Linear, cortical uptake along the POSTEROMEDIAL CORTEX of 1/3 of the tibial diaphysis


EARLY OSTEOMYELITIS in KIDS = Hot on all 3 phases, can have a cole/photopenic defect at metaphysis w/ increased uptake in adjacent diaphysis. Most common sites = Distal femur + proximal tibia

Salivagram = Detects aspiration


Milk scan = Detects and can grade GE Reflux (high level = mid esophagus, prolonged = reflux 10 seconds or longer)


Biliary Atresia vs. Hepatitis = BA = Liver uptake at 24 hours, no bowel, Hepatitis = No liver uptake and see bowel.

MAA Particle Reduction:

  • NEONATES = 10,000
  • Kids < 5 yrs = 50,000-150,000


RANDOM RADIOTRACER STUFF


MIBG = Norepinephrine (Pheochromocytomas, Carcinoid, Medullary Thyroid Ca, Retinoblastomas) . stop insulin, reserpine, TCAs, and amphetamine-like drugs before MIBG scan.


Octreotide = Somatostatin Receptor Analog (see uptake in Medullary Thyroid Ca, Small Cell Ca, Meningioma)


Typically CNS lymphoma, toxoplasmosis, bacterial abscess, Cryptococcus infection, and tuberculosis are all positive on Ga-67 scintigraphy whereas only CNS lymphoma will be positive on Tl-201.


Use Ga-67 for vertebral OM, since IN-111 doesnt really have uptake in spine. Use IN-111 for ABD INFECTION/INFLAMMATION since Ga-67 has physiologic bowel uptake.

Thallium-201 = Decays via electron capture to Mercaury-201, CRITICAL ORGAN = KIDNEYS, 73 HR 1/2 life, text

NRC STUFF
The dose limits of medical radiation exposure to the public is 100 mrem (0.1 rem) per year, or 2 mrem in any 1 hour.


  • GM counter should be calibrated ONCE A YEAR

PROTOCOLS:
-IN-111 = Label and reinject pt, then image 24 hours later (otherwise might get false positive with lung uptake)


-Bone scans w/ IN-111 and Tc-Sulfur Colloid = Do In-111 first, then Tc-SULFUR COLLOID for the marrow, wait 30 minutes after sulfur colloid before getting images

Neuro

  • Lewy Body Dementia = Although there can be hypometabolism in all of the above regions in Lewy body dementia, the hallmark finding in this type of dementia is reduced glucose metabolism in the occipital lobe on F-18-FDG PET.

ENDOCRINE and GI


-Normal Thyroid uptake at 24 hours is less than 35%

  • 15-20% of cold nodules are malignant
    -1% of hot nodules are malignant

Gallbladder Ejection Fraction? --> Values less than 38% are considered abnormal!