Nucleur Medicine imagery

what are the two types of radiation

non ionising radiation

• energy to make molecule/atoms vibrate to produce head

• not energetic enough to detach electrons from atoms/molecules

• mri uses non ionising radiation

ionising radiation

• energy to detach electrons from atoms/molecules = make ions

• we use in nuclear medicine

what are the two key ways ionising radiation is used

• ion directly damage DNA which we can use for treatment

• ionising radiation has enough energy to pass through body so we can use for imaging

e.g. x rays such as x ray and CT imaging

what is half life?

types of radioactive decay:

half life ( t1/2) = amount of time for radioactive decay(decays per second) to drop by half.

Alpha decay

• Higher damaging but stopped easily

• Good for treatment, bad for imaging

Beta decay

• Fairly damaging fairly easily stopped

Gamma decay

• Less damaging and very penetrating, great for imaging, bad for treatment

what is difference between radiopharmaceutical ( aka tracer) vs contrast agents

• tracers administered in lower conc and dont affect the process they are targeting

• radio-tracers radioactive, contrast agents aren’t

( if we can detect radiation we can build a picture of where tracer has gone in body and tracks the function it targets)

draw spider diagram for when we use each ‘thing’ in nuclear medicine in context of treatment and diagnosis

SPECT ( single photo emission computed tomography)

• include radiopharmaceutical used

• spect acquisition

• gamma ray produced when radiopharmaceutical decays creating 3D image

• Iodine (I)¹²³ and Technetium (Tc)^99m.

spect aquisition

• Patient is injected with radiotracer

• Gamma camera takes a 2d image  projection

• SPECT takes projections from different directions around patient

SPECT: the gamma camera

• include 4 key components and what they do

• draw rough diagrams

• what is a sinogram

gamma camera components r - how to make 3d images

(1) the Collimator - allows us to work out position of photon emission. Only ionising radiation parallel to collimator holes pass through scintillation crystal

(2) Scintillation crystal - converts ionising radiation into light photons

(3) Photomultiplier Tubes - light photons are converted into electrons before being significantly amplified in number

(4) Processing Electronics - positional and energy info is gathered. Image digitalized ready for display

sinogram = stack of projections taken at different angels

PET ( Positron Emission Tomography)

• PET acquisition

• radiopharmaceuticasls used

PET acquisition

• Patient lies inside the PET ring of detectors

• Radiotracer within the body emits a positron which annihilates (destroys) producing back-to-back photons

• Photons are measured by detectors in the PET ring

• If 2 photons are detected within a certain time frame then this is called a coincident event and a line of response (LOR) is drawn between them

PET radiopharmaceutical =Fluorine (F)¹⁸ 

PET:

• include key components

NOTE : PET USES SAME COMPONENTS AS GAMMA CAMERA BUT ARRANGED DIFFERENTLY

differences between PET and SPECT

PET	SPECT
Positron emission	Gamma emission
2 gammas detected	Single gamma detected
PET scanner is a ring of detectors	Gamma camera is 1 or 2 heads which rotate around patient
Position determined by line between 2 gamma rays	Position determined using collimators
Gamma rays 511keV	Gamma rays normally around 140keV

 

state and explain 2 examples of PET

1. glucose metabolism imaging ( how fast brain uses sugar)

• Radiopharmaceutical: F¹⁸ FDG = glucose analogue ( meaning body treats same as real glucose)

• used especially in epilepsy and dementia

2. amyloid imaging

• Amyloid beta: neurotoxic protein deposited in the grey matter in Alzheimer’s disease

• Radiopharmaceutical: F¹⁸ florbetapir

• f18 emits positrons we can measure and florbetapir sticks to amyloid beta plaques in brain

state and explain 2 examples of SPECT

1. perfusion imaging

• perfusion= blood flow to brain

• radiopharmaceutical : Tc^99m ECD

• Tc99m emits gamma rays which we can measure

  ECD delivered to the brain in proportion to the amount of blood flow to the brain region. it crosses blood brain barrier and gets trapped in brain cells

2. DATscan

• Radiopharmaceutical - I¹²³ Ioflupane

• I123 emits gamma rays which we can measure (with gamma camera)

• Ioflupane targets presynaptic dopamine transporter

• often used to diagnose parkinson’s

name 4 measures of image quality

noise
contrast
spacial resolution
artefact

noise - what is it and how to reduce it ?

what is it?

random statistical fluctuations make the image blurry

how to reduce it?
detect more photons - i.e. longer scan or bigger dose of radioactivity

contrast - what is it and how to increase it?

what is it?

difference between high and low areas of radiopharmaceutical uptake

how to increase it?

more iterations - although have to optimise for noise also

spatial resolution

• what is it

• how it impacts image quality in SPECT

• name 4 factors which affect spacial resolution in PET

what is it?

• Amount of blurring in the image

how it impacts image quality in SPECT

• determined by collimator geometry and distance to patient - angle of acceptance

name 4 factors which affect spacial resolution in PET
- crystal width
- anger logic
- photon noncollinearity
- positrons range

name two artefacts that are most prevalent in nuclear medicine imaging

• motion

patients moving during scans

to correct you have to align the SPECT projections before reconstructing

• attenuation

• The gamma photons emitted from the tracer need to reach the detector

• Attenuation = photons being absorbed or scattered in the body

hybrid imaging - CT

• include advantages and disadvantages of PET MRI over PET CT

• pet CT and spect CT because most are sold with a CT scanner attached. imaging is sequential for both.

• advantages and disadvantages PET MRI over PET CT

✓Great soft tissue contrast

✓scan simultaneously

✗worse for attenuation correction