PET: Principles of Operation

Question 1

PET is a — imaging technology used to assess — in the body, such as glucose metabolism, blood flow, and oxygen use.

Answer 1

non-invasive, metabolic processes

Question 2

It is widely used in – (to detect tumors), – (to study brain function and disorders like Alzheimer’s), and – (for heart disease imaging).

Answer 2

oncology, neurology, cardiology

Question 3

PET detects – emitted indirectly by a positron-emitting radiotracer injected into the patient

Answer 3

pairs of gamma rays

Question 4

PET is often combined with CT scans (PET/CT) to provide both functional and anatomical information in a single scan, improving —.

Answer 4

diagnostic accuracy

Question 5

PET was initially developed in the – for – but has evolved into a widely used clinical tool.

Answer 5

1970s, research in brain function

Question 6

The technique is based on the detection of positrons emitted by a radiotracer injected into the body. When a positron encounters an electron, they —, producing two 511 keV gamma photons that travel in —.

Answer 6

annihilate, opposite directions

Question 7

PET uses radiotracers such as FDG (—), which mimic – – –. For example, FDG is a – – used to assess glucose metabolism, which is often elevated in cancer
cells.

Answer 7

Fluorodeoxyglucose, natural biological processes, glucose analog

Question 8

— prepares a radiopharmaceutical for an examination of – with one of the first PET scanners (1975).

Answer 8

Michel Ter-Pogossian, Henry Wagner Jr

Question 9

– – occurs when a radioisotope decays, releasing a positron. Common radioisotopes include
– – –.

Answer 9

Positron emission, F-18, C-11, and N-13

Question 10

After traveling a short distance in tissue (a few millimeters), the positron encounters an electron, and – occurs.

Answer 10

annihilation

Question 11

– – convert the energy from gamma photons into visible light,
which is detected by – or – in the PET detector.

Answer 11

Scintillator crystals, photomultiplier
tubes (PMTs) or silicon photomultipliers (SiPMs)

Question 12

• Common scintillators include –, –, and – which are chosen for their high density and efficiency in detecting photons.

Answer 12

BGO (Bismuth Germanate), LSO (Lutetium Oxyorthosilicate), and LYSO (LutetiumYttrium Oxyorthosilicate)

Question 13

PET scanners use – – to ensure that only gamma photons from the same annihilation event are detected.

Answer 13

coincidence detection

Question 14

The system detects two gamma photons that are emitted at 180° apart, which helps to establish a – – – (–) between the detectors.

Answer 14

line of response (LOR)

Question 15

These LORs are used to construct a 3D image of the area being scanned, which represents the – – – —.

Answer 15

distribution of the radiotracer

Question 16

– – ensures that only paired gamma photons from a single
annihilation event are registered by the system.

Answer 16

Coincidence detection

Question 17

– –:
* Both gamma photons from a single annihilation event are detected within the allowed time window. These provide accurate data for image formation.

Answer 17

True events

Question 18

• Increases with system sensitivity

Answer 18

True events

Question 19

– –:
* One or both photons are deflected before reaching the detector, leading to inaccurate localization of the event.

Answer 19

Scatter events

Question 20

• Increases with body size, energy of the scattered radiation is less than 511 keV.

Answer 20

Scatter events

Question 21

– –:
* Two unrelated photons are detected simultaneously, which can cause artifacts in the image.

Answer 21

Random events

Question 22

• Increases with radioactivity level and sensitivity of the detectors

Answer 22

Random events

Question 23

Gamma photons emitted from deep within the body may be – or – by tissues, leading to underestimation of tracer activity in those regions.

Answer 23

absorbed or scattered

Question 24

compensates for this effect, ensuring more accurate representation of tracer distribution

Answer 24

Attenuation correction

Question 25

In PET/CT, a low-dose CT scan is often used to generate a -- -- --, which helps correct for photon attenuation

Answer 25

tissue density map

Question 26

TOF PET, TOF means?

Answer 26

Time-of-Flight

Question 27

TOF PET measures the -- -- -- -- of the two gamma photons at the detectors.

Answer 27

difference in arrival times

Question 28

By using this time difference, the system can -- -- the annihilation event along the LOR, leading to -- --.

Answer 28

better localize, sharper images

Question 29

TOF PET improves -- -- and provides -- -- --, especially in larger patients because of the reduction in the propagation of noise.

Answer 29

signal-to-noise ratio, enhanced spatial resolution

Question 30

PET systems are typically arranged with multiple rings of scintillator crystals surrounding the patient, which allows for ------.

Answer 30

full-body imaging in 3D

Question 31

The -- houses the detectors, which are organized into -- and -- for efficient photon detection and processing.

Answer 31

gantry, blocks and buckets

Question 32

Modern PET systems often include a CT component, enabling simultaneous acquisition of -- (PET) and -- (CT) images.

Answer 32

functional, structural

Question 33

The gantry houses the PET and CT detectors and forms the -- -- of the scanner.

Answer 33

physical framework

Question 34

It surrounds the patient and contains both the PET detectors (for functional imaging) and CT detectors (for anatomical imaging).

Answer 34

PET/CT Gantry

Question 35

moves the patient through the scanner to capture images from multiple angles

Answer 35

PET/CT Gantry

Question 36

The CT detector array is composed of -- that convert Xrays into electrical signals.

Answer 36

X-ray detectors

Question 37

The CT component provides anatomical images of the body, which are used for -- -- in PET and to provide detailed -- -- of functional abnormalities

Answer 37

attenuation correction, anatomical localization

Question 38

-- -- are arrays of scintillation crystals coupled with photomultiplier tubes (PMTs) or silicon photomultipliers (SiPMs).

Answer 38

PET detectors

Question 39

The -- -- convert the gamma photons produced by positron annihilation into light

Answer 39

scintillation crystals

Question 40

PMTs or SiPMs then convert this light into an -- --, which is used to calculate the location of the annihilation event

Answer 40

electrical signal

Question 41

A -- -- -- --uses a continuous ring of detectors surrounding the patient.

Answer 41

full ring PET scanner

Question 42

This design maximizes the coverage area and allows for simultaneous detection of positron annihilation events from all angles

Answer 42

full ring PET scanner

Question 43

Used for Full-body oncology scans and other clinical situations requiring high quality, comprehensive data.

Answer 43

full ring PET scanner

Question 44

full ring PET scanner: (advantage)

Answer 44

High sensitivity, Efficient Data Collection, Optimal for Large Volumes

Question 45

full ring PET scanner: (disadvantage)

Answer 45

Cost and Size

Question 46

-- -- -- -- use a rotating set of detectors that do not form a full 360-degree ring. Instead, they move around the patient to collect data from different angles.

Answer 46

Partial ring PET scanners

Question 47

Ideal for facilities with budget constraints or for applications that do not require extensive full-body imaging.

Answer 47

Partial ring PET scanners

Question 48

Partial ring PET scanners: (advantages)

Answer 48

Cost-effective, Flexibility

Question 49

Partial ring PET scanners: (disadvantages)

Answer 49

Lower sensitivity, Longer scan times

Question 50

The -- -- --moves the patient in and out of the gantry during the scan.

Answer 50

motorized patient table

Question 51

It ensures accurate positioning of the patient during scanning and moves smoothly to capture images at various positions along the body

Answer 51

motorized patient table

Question 52

The -- -- where the technologist or physician interacts with the PET/CT system

Answer 52

operator’s console

Question 53

The control console is used to configure -- --, control the --, initiate -- --, and -- the resulting images.

Answer 53

scanning protocols, gantry, data acquisition, process

Question 54

The -- also monitors the patient's condition during the scan

Answer 54

operator

Question 55

Image reconstruction in PET is typically done using iterative algorithms such as ------.

Answer 55

OSEM (Ordered Subsets Expectation Maximization).

Question 56

-- -- improves image quality and reduces artifacts, making it the preferred method in modern PET imaging.

Answer 56

Iterative reconstruction

Question 57

-- -- --provides objective data on the concentration of the radiotracer in specific tissues.

Answer 57

Quantitative PET imaging

Question 58

One common metric is the ------, It is a simple way to determine how much activity or FDG uptake there is on a PET scan in the tissues, which normalizes radiotracer uptake to patient body weight, injected dose, and decay.

Answer 58

Standardized Uptake Value (SUV),

Question 59

SUV is particularly useful in -- for assessing tumor activity and monitoring response to treatment.

Answer 59

oncology

Question 60

the radiotracer uptake in the tissue (in Becquerel per gram, Bq/g)

Answer 60

Tissue activity concentration

Question 61

total activity of the radiotracer administered (Bq)

Answer 61

injected dose

Question 62

patients weight (g)

Answer 62

body weight

Question 63

--- ---: A 68Ge or 68Ga source is used to generate a uniform signal across all detectors. This scan checks for -- -- --.

Answer 63

Blank Scan, uniform detector response

Question 64

* -- -- and --: The CT component of the PET/CT scanner undergoes -- -- --- to ensure consistent X-ray output. Calibration checks the accuracy of -- -- measurements for CT.

Answer 64

CT Warm-up and Calibration, Xray tube warm-up, Hounsfield Unit (HU)

Question 65

Daily Calibration, What to Check: --- --- --: Check for any malfunctioning detector blocks (e.g., "bad blocks" which can cause image artifacts).

Answer 65

Detector block status

Question 66

Daily Calibration, What to Check: -- -- --: The result should be a uniform signal across all detectors without any visible “cold” or “hot” spots.

Answer 66

Uniformity of Response

Question 67

Daily Calibration, What to Check: Expected Result: A ------- (no gaps or irregularities in the detector array). If issues are found (e.g., dead pixels or blocks), corrective actions should be taken before any patient scans are performed

Answer 67

uniform blank scan with no anomalies

Question 68

daily calibration

Answer 68

blank scan, CT warm-up and calibration

Question 69

weekly calibration

Answer 69

High Count Rate Blank Scan, CT Spatial Resolution Test, Single Gain Update

Question 70

-------: Similar to the daily blank scan but performed over a longer duration to collect more counts and verify system performance at higher activity levels

Answer 70

High Count Rate Blank Scan

Question 71

CT Spatial Resolution Test: Use a -- to verify the spatial resolution of the CT component.

Answer 71

phantom

Question 72

-------: Calibration of detector gain, ensuring that the signals from all photomultiplier tubes (PMTs) or silicon photomultipliers (SiPMs) are uniform.

Answer 72

Single Gain Update

Question 73

Weekly Calibration, What to Check:

Answer 73

Detector Sensitivity, Image Registration

Question 74

Weekly Calibration, What to Check: Expected Result: A -------- with proper alignment of PET and CT images. The -- -- should ensure that all detectors respond uniformly to gamma photons

Answer 74

uniform & high-quality blank scan, gain calibration

Question 75

Quarterly Calibration:

Answer 75

Distortion Tests, Well Counter Calibration, 2D and 3D Calibration, Normalization of Detector Efficiency

Question 76

---: A phantom with known dimensions is scanned to verify there is no image distortion in PET and CT

Answer 76

Distortion Tests

Question 77

Well Counter Calibration: This ensures the accuracy of -------- by calibrating the well counter used to measure radiopharmaceutical activity.

Answer 77

Standardized Uptake Values (SUV)

Question 78

2D and 3D Calibration: This involves calibrating the individual slices in 2D and 3D modes, ensuring that all planes of the PET image are ---- --- and ---.

Answer 78

properly aligned and normalized

Question 79

Quarterly Calibration, What to Check:

Answer 79

Spatial Resolution and Sensitivity, Normalization Maps

Question 80

Quarterly Calibration, What to Check: Expected Result: Accurate -- -- and precise - - for quantitative analysis. Normalization ensures that the system maintains consistent sensitivity and spatial resolution across the field of view

Answer 80

distortion-free images, SUV values

Question 81

Yearly Calibration:

Answer 81

Complete System Calibration, CT HU Calibration, Comprehensive Quality Assurance (QA) Testing, Maintenance Check

Question 82

-- -- --: All detectors are recalibrated to account for any wear or degradation in performance over the year.

Answer 82

Complete System Calibration

Question 83

-- -- --: A phantom with different known densities is scanned to verify that the CT accurately represents the Hounsfield Units (HU) for air, water, and bone.

Answer 83

CT HU Calibration

Question 84

--------: Includes detailed checks of spatial resolution, contrast resolution, sensitivity, and quantitative accuracy for both PET and CT systems.

Answer 84

Comprehensive Quality Assurance (QA) Testing

Question 85

Maintenance Check: Includes -- --(e.g., checking the X-ray tube in CT) and -- --to ensure the system is operating with the latest versions.

Answer 85

hardware maintenance, software updates

Question 86

Yearly Calibration, What to Check:

Answer 86

Complete System Functionality, Accuracy of Quantitative Measures