PET oral test out

Why do we glucose test patients before a FDG PET scan?

If a patients blood glucose is too high it will cause our tracer to not bind to what we want it to as well (competitive binding)

Normal values for a blood glucose level for a PET scan?

70-200 mg/dL

What if the patients blood sugar is too low?

Make sure that the glucose machine isn't broken/test again and give some juice to try and raise their blood sugar

What do we do if the patients blood sugar is too high?

Either give insulin and wait 4 hours or wait until you get a blood sugar you want if you have enough dose

How to do a FDG PET scan?

explain test, check blood glucose level, start IV, go to injection room, hook up to intego or give unit dose, 10-20mCi, wait 45-60 minutes, give patient a blanket/quiet room, patient voids before exam, scout image performed to map out body, then CT performed, then PET scan

Patient prep for FDG PET scan?

NPO 4-6 hours prior, diabetic medications stopped (insulin 4-6hrs, oral 4-6hrs), no exercise for 24hrs, no caffeine, high protein low carb diet

Why no exercise for 24-48 hrs?

Exercise causes binding of FDG in the muscles and this will ruin our test because it will not go to what we want it to

What will happen if the patient eats before the exam?

Possible competitive binding with blood sugar and there will be more bowel uptake because of bowel muscle movement

What are the instructions for the patient after injection of the RPx?

Need to relax and be warm, must give a blanket to keep from shivering, have them sit in a chair that is comfortable and in a quiet room

Why does the patient need to be well hydrated?

To clear the bladder quick and have good veins for IV

What does colorectal cancer look like on a PET/CT scan?

Focal hotspot on the colon

How long should a patient stop breast feeding after a PET scan?

12 hours

Normal organs that show up on a PET scan?

brain, heart, liver, bladder, testes, salivary glands

Clinical indications of a PET scan?

staging cancer, restaging cancer, post treatment assessment, malignant vs benign tumors, primary tumors, radiation therapy planning

Contraindications for a PET scan?

Blood glucose over the limit, food/sugar before test, if pt exercised, blood sugar is too low, smoking

What happens if insulin is given when blood glucose is too high?

It will cause increased muscle uptake

What do type 2 diabetes patients do if they are having a PET scan?

Follow prep directions like normal unless otherwise instructed by a doctor

What do type 1 diabetes patients do if they are having a PET scan?

Can be scheduled for mid-day/late afternoon, can have light meal and take insulin (must wait 4 hrs)

What if a prostate cancer patient comes in and cannot empty his bladder well, what could we do to make his bladder not so hot?

Use a diuretic (lasix), give plenty of water to help empty them or catheterize them

What kind of artifacts are there for PET scans?

Motion, truncation, metal artifacts, pulse pile up

What is truncation?

CT fov is smaller than the PET fov causing larger patients to have arms cut off in the pictures

How can we fix a truncation artifact?

By imaging the patient with the arms up

What is resolution?

Can differentiate two points from one another

What is a true?

Annihilation reaction occurs and 2 photons hit the detector causing a LOR to form (basis for PET)

What is a random?

When two photons hit the detector but they are from different annihilation reactions causing an incorrect LOR (may correct this with timing window)

What is a single?

When a single 511 keV photon strikes the detector

What is scatter?

When an annihilation reaction occurs and 1 of the 511 keV photons changes direction

What is a multiple?

When 2 or more annihilation reaction photons hit the detector at the same time

Which crystal has the highest stopping power?

BGO (has a longer dead time)

BGO vs LSO?

-LSO: Lower stopping power, faster scintillation, and more light output

-BSO: good stopping power, smaller light output, and poor energy resolution

What is light output?

the number of scintillations produced by each incident photon

Special melanoma consideration for PET scan?

-whole body scans, sit for 45 minutes, can originate/spread anywhere

How do we diagnose melanoma?

biopsy and doing histology stuff

What is a sinogram?

are individual slices of the scan stacked on top of each other

What does a sinogram help you determine?

If there is a black streak, then you know you have possible misalignment

What is the half life of F-18?

110 minutes

What is the half life of Rb-82

75 seconds (generator produced)

What is the half life of C-11?

20.3 minutes

What is the half life of N-13?

10 minutes

What is the half life of O-15?

2 minutes

What is the half life of Ga-68?

67.7 minutes (generator produced)

Mechanism of localization for FDG?

glucose metabolism

Mechanism of localization for NaF?

Osteoblastic activity

What is the order of a PET scan?

topogram (scout CT), CT, and PET

When should you perform PET QC?

In the morning so that if there is any errors you correct them before injection of patients

How do you scan a patient with melanoma?

Arms down because it could be on their arms

What process can affect our scan?

Any metabolic process will show increased uptake (tumor, fractures, brain, heart)

False positives in PET?

infection, inflammation, muscle, brown fat, thymic rebound, graves/hashimotos, fractures

False negatives in PET?

Low-grade malignancies can be the same metabolic state as normal surrounding tissue causing a false negative

Why do we do PET/CT?

attenuation correction and anatomical reference

What are SUVs?

standardized uptake value, measures amount of FDG uptake and can give a little bit of an indication if a spot is benign or malignant

Non AC vs AC images?

AC images have lighter lungs and skin, Non AC has darker lungs and most of the body looks hotter

What crystals can be used for time of flight imaging?

LSO crystal because of fast scintillation time

What is time of flight?

Measures the difference on arrival times, can help pinpoint spot where annihilation occurred

2D vs 3D PET?

2D has septa and 3D does not

Partial volume effect?

smaller object looks larger, degrades images resolution, hotter spots look colder, and colder spots have more counts

Why is brown fat bad for a PET scan?

causes false positives on our exams

What is brown fat?

specialized form of heat producing tissue and is very metabolically active

Time of flight vs non time of flight cameras

Tof cameras have much higher resolution because they can determine exactly where on the LOR the annihilation event took place

Advantages of F-18 FDG

can be used for a multitude of different tests and is widely available, 110 minutes half life, and cyclotron produced

Disadvantage of F-18 FDG

Most everything in our body is metabolically active so false positives can occur, need to keep patient in a fine balance

Advantage of Rb-82

Good at assessing myocardial perfusion and produces better pictures then SPECT, used with larger BMI patients or those that cannot tolerate SPECT imaging

Disadvantage of Rb-82

Expensive because you need a generator, short half life, and insurance does not always cover PET hearts

NaF F-18 advantage

Good at assessing bones for same indications as a general nuc med bone scan, better image quality with PET

NaF F-18 disadvantage

Not really covered by insurance providers due to bone scans being "good enough"

N-13 advantages

very high first pass extraction

N-13 disadvantages

Very short half life (9.9 min)

Why would the heart show up really hot?

The heart will sometimes use glucose for its energy source as well but ideally we would want it to be in a fatty acid metabolism

Effect of radiation therapy and chemo on a PET scan?

Chemo increased bone marrow uptake and radiation therapy can cause tissue necrosis or radiation pneumonitis that can affect our test

What is volume averaging?

when 2 pixels are averaged out (decreases brightness of an object) thus decreasing spatial resolution

partial volume effect

Process by which different tissue attenuation values are averaged to produce one less accurate pixel reading. Also referred to as volume averaging.

Why would we do a WB immediately after a bone scan?

WB PET is more sensitive than planar/SPECT imaging

NaF use?

5-10 mCi for bone imaging the procedure is the same except we do not need a blood glucose

How would a bad nodule show up on a sinogram?

Empty column or "break"

MLEM & OSEM why is it most used?

most common types of iterative reconstruction because of speed

What does MLEM and OSEM do?

compares estimated distribution across LORs to acquire projection, corrects LOR errors, Randoms, scatters, and attenuation

How many beds for an eyes to thighs scan?

5-7 beds

When is WB imaging done?

cancer in head or legs and requires more than 10 beds

What sets PET apart from general nuclear medicine?

higher photon energies for PET

Normalization accomplishes what?

uniformity, setting the reference

Daily QCs on a PET scanner?

Need to do all the QC for CT like air calibration check and the water phantom and then do the PET germanium source for the PET daily QA

What is a blank scan?

Done daily, keeps attenuation maps correct, shows all possible angles from one coincidence via criss cross set of lines

What is an LOR?

A line representing the path of the annihilation photons usually 180 degrees and we can predict the location of the reaction from this

Advantages of respiratory gating?

Can help negate the effects of breathing and provide a more accurate interpretation of pulmonary nodules

Disadvantage of respiratory gating?

sampling too large of a portion of the respiratory cycle can cause potential for adding more motion artifacts

Why do we have patient in a dark room for FDG dementia?

minimize brain activity which would avoid false positives or high uptake in an area of unnecessary activity

Why is it hard to identify lower lobe lung nodules?

Because breathing artifacts can cause confusion with the liver

Method of localization of F-18

chemisorption

Method of localization of O-15 water

passive diffusion