PET/CT

Positron emission tomography (PET)

medical imaging technique which allows quantitative in vivo measurements of 3D distributions of positron-emitting tracers. 

18F-fluorodeoxyglucose (FDG)

is the most commonly and widely used PET tracer in oncological applications.

glucose consumption

FDG basically provides a measure of _______________________, and it is mainly used to detect malignancies

vivo

PET is a molecular imaging technique which measures the distribution of a radioactive tracer in ______. 

therapeutic responses; efficacy of new drugs.

PET can be used for assessment of _____________________ as a clinical application or for the evaluation of the _______________________

511

The positron and electron are then converted into two photons, each having an energy of _____ keV, which are emitted in nearly opposite directions (180 degree). PET image acquisition is based on the simultaneous (coincidence) detection of these two photons. 

annihilation coincidence detection

this process is the hallmark of PET imaging

Random coincidence

coincidence detection of 2 uncorrelated photons

Scatter coincidence

coincidence detection of one or both photons from a single event produced from Compton scattering

True coincidence

arise from the simultaneous (coincident) detection of 2 annihilation photons generated by 1 positron emission

1. Random Correction

2. Attenuation Correction

3. Scatter Corrrection

Correction methods

2 different positron emissions

Random coincidence arise from the ‘simultaneous’ detection of  2 uncorrelated photons, i.e. photons coming from ______________________.

uniform background

As these randoms are uncorrelated, their mutual directions are also uncorrelated and an almost ___________________ is added to the measured 3D activity distribution. 

block singles; delayed coincidence time window method

Nowadays most PET-CT systems use sophisticated random correction methods based on using either ___________________ or a _______________________

loss of coincidences

Attenuation of photons in the patient causes ___________________

CT data

In PET/CT, ___________ is used to derive attenuation correction (CTAC)

compton scattering

The main cause of scattering events for 511-keV photons is ________________, where the photon interacts with (‘hits’) an electron.

single scatter simulation method

The most frequently applied scatter correction method in PET is based on estimating the scatter distribution/contribution using a ____________________ described by Watson et al

• O-15

• N-13

• C-11

• F-18

commonly used positron-emitting radioisotopes are based on atoms found in organic substances

• Differentiation of benign from malignant lesions

• Searching for an unknown primary tumor

• Staging and response assessment

• Inflammation & infection imaging, cardiology, and neurology

Main indications of PET/CT

• Chewing gum

• Obesity

• Cold Exposure

• Increased Glucose Levels

• Intravenous Insulin Administration

• Coffee or caffeinated beverages

• Metformin

PET/CT contraindications

masticatory muscles

Patients are also advised not to chew gum for 24 h before the study to avoid activation of ___________________

obese

PET scan may not be possible if you are _______ and unable to fit into the scanning chamber (gantry).

• 425 to 450 pounds,

• 27.5 inches

The scanning table has a maximum weight capacity of _____________, while the gantry has a diameter of only _____________ (70 centimeters). Image quality may be degraded if weight and size limits are exceeded.

Cold exposure

is known to stimulate BAT via an adrenergic mechanism which is more pronounced during fasting

malignant lesions

Prominent 18F-FDG uptake within brown adipose tissue (BAT), which normally has a role in nonshivering thermogenesis, can potentially mask or mimic ________________

glucose transport

Blood glucose levels can have a significant influence on tumor 18F- FDG uptake because 18F-FDG and glucose compete for _________________ and phosphorylation by hexokinase

Increased

_____________ glucose levels decrease 18F-FDG uptake in the brain and in tumors because of direct competition between binding sites and enzyme

Intravenous Insulin Administration

Increases the translocation of GLUT4 (glucose transporter), thereby rapidly and efficiently shunting 18F-FDG to organs with a high density of insulin receptors (e.g., skeletal and cardiac muscles), resulting in altered radiotracer biodistribution and suboptimal image quality

Coffee or caffeinated beverages

are not recommended because even if “sugarless” they may contain traces of simple carbohydrates and have the potential to induce excitant effects; this may also be the case for “sugar-free” beverages

Metformin

Prominent 18F-FDG bowel uptake, which can compromise image quality, has been identified by multiple investigators with use of _______________

4.7 mGy

The International Commission on Radiological Protection (ICRP) reports that for an adult patient the administration of 259 MBq (7 mCi) of FDG results in an absorbed radiation dose of _______ to the nongravid uterus (i.e. 1.8×10−2 mGy/MBq)

iodine-based contrast dye

If undergoing a combination PET-CT scan, the ___________________ used for the CT component can cause side effects, including nausea, vomiting, headache, itching, flushing, and mild rash.

anaphylaxis

In rare cases, a serious, all-body allergic reaction known as __________ may occur