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Fundamentals of P > X-Ray, CT, PET > Flashcards

X-Ray, CT, PET Flashcards

1
Q

List imaging types with Ionising Radiation

A 
Ionising Radiation
Planar X-ray
CT
Gamma Camera and SPECT
PET
Hybrid Imaging
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2
Q

What is ionising radiation?

A

Radiation that causes ionisation when it interacts with matter

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3
Q

Types used for medical imaging are:

A

Gamma rays

X-rays

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4
Q

Why use ionising radiation?

A

Why use ionising radiation?

Penetrating

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5
Q

Ionising Radiation Action

A

Indirect Action –
Majority of the body is water

Production of Free Radicals & Hydrogen Peroxide

FR are highly reactive, so direct action = mutation in cell DNA

= biological response = genetic, death, cancer

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6
Q

Direct effect of radation damage

A

Only at high radiation dose not noticed at usual diagnostic doses
Threshold effect
e.g. Erythema & hair loss

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7
Q

Indirect effect of radation damage

A

Indirect effects
Risk of cancer induction
Risk of genetic change in subsequent population
Effect is proportional to radiation dose, no threshold
🡪 all radiation has risk

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8
Q

Some typical effective doses (mSv) are:

A 
Some typical effective doses (mSv) are:
Dental intra-oral	0.002
Chest X-ray		0.02
Lumbar Spine		2
NM Bone Scan  	3
IVU				4
CT pelvis			7
CT head			2
Barium enema		8
MIBI cardiac scan     10
PET scan 		        10
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9
Q

Risk of fatal cancer induction is:

A

Risk of fatal cancer induction is:
5% per Sievert
1 in 20000 per mSv
1 in 2000 per PET scan

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10
Q

Annual radiation dose in the UK average = ?

A

Annual radiation dose in the UK average 2.7 mSv

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11
Q

Positrons - effect

A

Positive electrons interact with matter to create gamma rays = PET

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12
Q

Gamma rays - effect

A

Penetrating radiation = Gamma camera imaging

e.g. SPECT

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13
Q

X-rays - effect

A 
X-rays
Spectrum of electromagnetic
	radiation = X-Ray imaging
e.g. radiographs,
CT

Artificially produced in an X‑ray tube

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14
Q

Relation of positrons’ and gamma rays’ emission

A

Emitted following the radioactive decay of an unstable nucleus

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15
Q

Attenuation increases with

A

Attenuation increases with
Higher atomic number
Higher density
X-Rays are essentially an attenuation map

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16
Q

Transmission Imaging - action and advantages

A

Transmission Imaging
Radiation is directed through the patient
A transmission map collected is essentially an attenuation map
Good at showing structure, especially between tissues of different densities or atomic number

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17
Q

Emission Imaging - action

A

The radiation is administered to a patient in the form of a tracer
Emitted radiation is detected outside the patient

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18
Q

Voltage/current function in X-ray tube

A

High voltage controls the energy of the x-rays

Current control the amount of x-rays

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19
Q

X-ray produced when and how much control do we have

A

X-rays only produced when tube is in action i.e. can be switched on/off
We have control over the amount and energy of x-rays produced

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20
Q

Detectors for planar X-ray - Film Hardcopy = describe action

A

Film processor with tanks of chemicals

High resolution

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21
Q

Detectors for planar X-ray - Computed Radiology computer copy
= describe action

A

Phosphor plate
Special laser scanner or CR reader that reads and digitizes the image
Digital enhancement and archiving

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22
Q

Detectors for planar X-ray - Digital Radiology (DR)

= describe action

A

Flat panel detector, fully digitised system

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23
Q

PE X-ray description

A

Wedge shaped defect 🡪 Pulmonary embolism

Only large PE can be seen on X-ray

24
Q

X-Ray Screening: Mammography = describe action and advantages

A

High resolution
Compression plate used to reduce breast thickness
Improves resolution
Lowers radiation dose (used as a screening tool)

25
Q

Real-time X-ray: Fluoroscopy - action and use

A

Real-time imaging
A catheter is fed inside an artery and radio opaque dye is injected
Show blood flow inside vessels and can be used to assist with interventions

26
Q

X-ray intervention:

Coronary angiography - action

A

Real-time imaging using an image intensifier called fluoroscopy

A cardiac catheter is fed inside the aorta
Radio-opaque contrast agent used to identify areas of occlusion

Treatment may be either balloon angioplasty or insertion of a stent

27
Q

Limitations of Planar X-ray

A

Cannot distinguish between overlying tissues
Tissues other than those being observed reduce contrast in the image
Historically partially solved by moving the film cassette and X-ray relative to the patient to blur out overlying tissues, called “tomography” (from Greek “part/slice” - “write”)
Superseded by Computed Axial Tomography, now abbreviated to CT

28
Q

Helical scanning - action

A

Helical scan is a method of recording high-frequency signals on magnetic tape

Continuous rotation
Continuous table feed

29
Q

Helical MSCT - advantages

A

Multi-slice
Faster scan
More coverage each rotation

30
Q

CT acute diagnosis:

Haemorrhage or blood clot? - what is needed and why

A

Urgent diagnosis required for treatment

Clot busting drugs may increase bleeding

31
Q

CT: Disease progression - use of imaging and any measurements done

A

Measurement of the size of the left inguinal lymph node shows progression of disease
Imaging is used for monitoring response to therapy

32
Q

CT in Treatment Planning

A

External beam radiotherapy irradiates normal tissue as well as tumour
Multiple beams are used to spare normal tissue
CT is used to define area to be treated and the direction of the radiotherapy beams that are used

33
Q

Functional Imaging - action

A

Inject radioactive tracer, patient is emitting the gamma rays
Image depends on the metabolism of the tracer: Functional Imaging

34
Q

Gamma camera - what does it use and +ves

A

Uses single photon emitting radionuclides

Can operate in 2D (planar) or 3D (SPECT)

35
Q

PET - uses what and characteristics

A

PET
Positron Emission Tomography
Uses positron emitting radionuclides
Always 3D

36
Q

Why is nuclear medicine a functional modality

A

Nuclear Medicine only shows function
It may reflect anatomy but without metabolism, the tracer will not be taken up
Nuclear Medicine is a functional modality

37
Q

Half-life- define

A

Half-life is time taken for the radioactivity to reduce to 50%

38
Q

Gamma Camera Imaging - function of imaging heads

A

Gamma cameras have imaging “heads”

For radionuclides that decay with direct emission of gamma rays

39
Q

Most common radionuclide

A

Most common radionuclide is Tc-99m (T1/2 = 6 hours)

40
Q

Tracers used in gamma camera imaging:

A

Tracers used in gamma camera imaging:
Tc-99m MDP (bone scans)
Tc-99m DTPA (kidneys)
Tc-99m White Cells (infection/inflammation)

41
Q

Dynamic Renal Transplant Scan - action

A

Camera positioned above the patient
Tc-99m DTPA injected IV
Camera positioned above the patient
Gamma camera records gamma rays and collects image over time
Functional Time –Activity curves are obtained

42
Q

SPECT - define + +ves

A

SPECT is a nuclear imaging scan that integrates computed tomography (CT) and a radioactive tracer (observe BF)

Acquire up to 64 images from around the head

Reconstruction of transaxial slices

43
Q

DaTSCAN - define and action

A

A DaTSCAN is a scan of the brain. DaTSCAN contains the active substance ioflupane (I123) which is used to help diagnose abnormalities in the brain.

Binds to the dopamine transporters (DAT), on the neurons

44
Q

β+ Particle Radiation - effect

A

Both positron and electron are annihilated

2 gamma rays are created at 180o to each other

45
Q

β+ Particle - define

A

A beta particle, also called beta ray or beta radiation, is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay

46
Q

FDG - define + allows what

A

FDG is a glucose analogue which enters cells in the same way as glucose

Allows = good reflection of the distribution of glucose uptake and phosphorylation by cells in the body

47
Q

Metabolism of FDG

A

Glucose in blood → Glucose in cell → Glucose-6P (by phosphorylation) → Glycolysis

FDG in blood → FDG in cell → FDG-6P by phoshphorylation but then it is metabolically trapped

48
Q

PET Scanner - action

A

A ring of scintillation detectors supported in a fixed gantry

Operated in “coincidence mode” - only photons emitted from an annihilation event are recorded

49
Q

PET Coincidence - describe

A

2 gamma rays originate from one annihilation event

Both are detected within a short time (a few ns)

Defines ray path for subsequent reconstruction of image

50
Q

Alzheimer’s disease characteristics

A

Alzheimer’s disease (hypometabolism, mostly in temporal and parietal regions)

51
Q

Pick’s disease characteristics

A

Pick’s disease (fronto-temporal hypometabolism)

52
Q

High resolution - types of scans

A

High resolution
CT
SPECT
PET

53
Q

Hybrid Imaging - examples

A

PET-CT
SPECT-CT
PET-MR

54
Q

Role of CT in localisation

A

Fused PET & CT show the exact location of the “hot spot”

55
Q

Attenuation - describe

A

Gamma rays originating from the centre of the patient will travel through more tissue which mean they are attenuated more
The CT image is used as an attenuation map to correct the PET image

Fundamentals of P (62 decks)

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