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CSH059 Imaging > PET > Flashcards

PET Flashcards

1
Q

What is nuclear medicine?

A
  • applies unsealed radioactive substances, administered in the form of radiopharmaceuticals

Used for the diagnosis and treatment of disease

Non-invasive imaging aimed at capturing functional and metabolic images of the target body tissue.

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2
Q

What is the process of Nuclear Medicine

A

A small dose of a radioisotope is administered to the
patient in the form of a radiopharmaceutical or tracer,
which is designed to enter the cells of the target organ.

The radioisotope decays to emit energy in the form of
gamma radiation that can be detected by the gamma
camera or PET/CT Scanner.

Scanned data represents the distribution and uptake of the tracer in the body

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3
Q

What is radioactive decay?

A

◦ decay is spontaneous process aimed at achieving stability in the atom

◦ Decay can result in the emission of energy in the form of
electromagnetic radiation or the emission of particles.

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4
Q

Unit of radioactive decay

A

The unit of radioactivity is the Becquerel (Bq)

One Bq. corresponds to 1 decay per second

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5
Q

What is the half-life

A

Half-life is the length of time that it takes for an element to decay to half its activity.

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6
Q

When a nucleon is transitioning from excited state back to ground state, energy is released in the form of…

A

electromagnetic radiation - Υ ray (gamma ray)

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7
Q

When an electron transitions from the excited state back to the ground state, energy is released in the form of…

A

electromagnetic radiation - X rays

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8
Q

What is SPECT Imaging

A

Camera rotates around the patient recording multiple images that are then reconstructed into a 3-D data set

Cross sectional imaging

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9
Q

Disadvantages of sole SPECT imaging

A

◦ Low resolution leads to decreased reporting confidence
◦ Acquisition times long, motion a problem
◦ Lack of anatomical landmarks

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10
Q

What is the benefit of SPECT CT

A

Combines the low resolution of SPECT with High Resolution of CT

Provides specificity to the image interpretation

Allows for image attenuation correction, localisation and registration

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11
Q

How is SPECT CT beneficial to RT

A

CT images for SPECT are typically LDCT’s and their purpose is for attenuation
correction, image co-registration for the purpose of pathology localisation

Once the CT is imported and registered to the RT planning data the nuclear
medicine metabolic data can then be accurately used to assist with
treatment planning

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11
Q

How is SPECT CT beneficial to RT

A

CT images for SPECT are typically LDCT and their purpose is for attenuation
correction, image co-registration for the purpose of pathology localisation

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12
Q

How to maintain radiation safety

A

Time - reduce time spent surrounding the patient

Distance - maintain distance between the patient and yourself (distance greater than 1.0m shown to be effective when communicating)

attempt to schedule around other procedures especially ultrasound which does require close contact

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13
Q

PET overview

A

◦ provides metabolic and functional imaging
◦ Uses short lived positron emitting isotopes
◦ uses annihilation coincidence detection

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14
Q

How are short-lived positron emitting radiopharmaceuticals created?

A

Cyclotron - stores isotropes used to make radiopharmaceuticals

A cyclotron is a type of particle accelerator which repeatedly propels a beam of charged particles (protons) in a circular path

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15
Q

What is positron decay

A

Positron decay is a way for an atom with too many protons to achieve a more relaxed state

P + -> n + e + + neutrino + energy

A proton in a nucleus is transformed into a neutron and a
positively charged electron – or a positron.

The positively charged electron and a neutrino are ejected
from the nucleus

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16
Q

What is a positron?

A

A positron is the antiparticle of an ordinary electron

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17
Q

What happens to a positron once ejected from a nucleus?

A

 After ejection from nucleus it loses kinetic energy in collisions with atoms in surrounding matter and comes to rest within millimetres of the site of origin (10 -9sec)

 The positron then combines with an ordinary electron in an annihilation reaction

 In which its mass and that of the ordinary electron are converted into energy

 This energy appears in the form of two 0.511MeV annihilation photons

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18
Q

PET/CT relation to annihilation photons

A

 PET uses annihilation coincidence detection to create the image

 This is based on two 511kev photons are emitted in opposite directions following the annihilation of a positron and an ordinary electron

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19
Q

Why is attenuation correction important in PET/CT

A

Photons from deep in the tissue are absorbed –> therefore need to correct for depth

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20
Q

Where can the attenuation coefficient be applied in PET/CT

A

Where the tissue structure is relatively uniform’ e.g. the head, a standard attenuation value can be used uniformly across the structure

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21
Q

What was the motivation for PET/CT

A

The motivation for the development of PET/CT was the need to be able to identify areas of increased
radiopharmaceutical (metabolic information) with patient-specific anatomy under identical “conditions”.

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22
Q

How can malignant tumours be visualised on a PET/CT

A

 Increased glycolysis is a distinct marker of malignant tumours compared to normal tissue

23
Q

Typical biodistribution of FDG throughout the body

A

The Brain
 High Uptake - Cortical and cerebellar grey matter, nuclei, and thalamus
 Low/No Uptake - White matter and ventricular system

Body
 Liver > Spleen
 Mediastinum (blood vessels)
 Kidneys, Ureters and Bladder
 Muscles and Bone Marrow

24
Q

What is the standardised uptake value

A

 SUV is a relatively simple, reproducible and well-established
index for quantifying glucose utilisation by measuring the
activity of tracer in the lesion or organ corrected for the
patient’s weight and dose of FDG injected.

provide an objective assessment of therapy response on serial PET scans

25
Q

Patient preparation for FDG imaging

A
  • 6 Hour Fast - Nothing to eat or drink other than plain water with no additives
  • Refrain from strenuous exercise 24-48 hours prior to scan
  • Diabetics must discus current therapy and special requirements with the department to
    insure insulin levels are correct
26
Q

Why is lorazepam sometimes utilised for PET scan

A
  • Reduces muscle activation within
    the neck and relieves tension. Also used for patients
27
Q

How can brown fat affect PET imaging

A
  • Mitochondria-packed brown fat cells burn energy and rapidly produce heat
  • 18F-FDG uptake in brown fat is a potential confounder in the interpretation of PET images, because the presence of brown fat may obscure or lead to erroneous diagnosis of lesions

Beta blockers can be given an hour to scan

28
Q

What is brown fat

A

Brown fat (brown adipose tissue) is a type of body fat that regulates your body temperature in cold conditions

29
Q

How to ensure excellent cardiac suppression on PET

A
  • 48 hours prior to imaging we ask the patient to follow a high fat, low carb diet -> ensurs heart is using fatty acids and glucose as an energy source when FDG is administered
  • Heparin may also be used 15 minutes prior to injection to stop non-specific myocardial uptake by increasing free fatty acid availability

Steps used with tumours located around/within the heart

30
Q

How does crystal size in the PET detector correlate to spatial resolution and detectability

A

Reducing crystal size –> improve spatial resolution and detectability

31
Q

What are the benefits of Biograph Vision Quadra PET CT scanner

A

 Decreases the time of scan which will allow us to decrease the dose administered to the patient significantly to achieve reductions in ionising radiation

FOV -> 106 cm

32
Q

What is a PET/MRI

A

combination of the metabolic information from a PET scan with the superior soft tissue and morphologic imaging offered by MRI

33
Q

What is rigid-coregistration?

A

LDCT from PET session is fuse to the simulation/planning CT

Spatial transformation is then applied to the respective PET (translation or rotation)

34
Q

What is deformable co-registration

A
  • Allows for registration beyond translation and rotation
  • deformable algorithms “warp” the PET data set to match the reference image (QA is needed when applying to check PET and LDCT perfectly aligned)
35
Q

Disadvantages of Hybrid Imaging

A

Differences in breathing patterns
- CT – breath hold
- PET – tidal breathing
- Mis-registration

High density contrast agents (eg barium) and
metallic objects (eg pacemaker, hip
replacement)

-overestimation of FDG activity if CT data is
used for attenuation correctionq

36
Q

Where do meningiomas arise from

A

 Meningiomas arise from the dura of the brain / spinal cord

37
Q

Effects of Meningioma and epidemiology

A

 Are the most common intracranial tumour – accounting for
almost 30% of all primary intracranial tumours (higher incidence in female 3:2)

 Progressive enlargement of the tumour and compression of
the neural tissue lead to clinical manifestations such as seizure disorders, focal neurological deficits and neuropsychological decline

38
Q

Precision Medicine

A

tumours are heterogenous -> radiopharmaceuticals are chosen by facotring in the biology, physiology and molecular profiles

39
Q

Disadvantages of FDG usage

A

 Tumour must have upregulation of the Glut1 receptor to be
detected

  • poor at early response to assessment
40
Q

What gene does meningiomas overexpress

A

Meningomas demonstrate overexpression of SSR2

Because of this, Ga68 DOTATATE which acts as a SSTR2
analogue has been found to be of value

41
Q

What is Ga 68 DOTATATE

A
  • Ga 68 Dotatate is routinely used for diagnosis and staging of well differentiated neuroendocrine tumours..
  • It provides functional imaging by acting as a somatostatin analogue
  • DOTATATE binds to somatostatin receptors (SSTR) and in particular, binds to SSTR sub-type
42
Q

Benefits of GA68 DOTATATE use for Meningiomas

A

 Ga68 DOTATATE PET/CT has been shown to assist with
◦ target volume delineation
◦ Stereotactic surgical planning
◦ Diagnosis of small meningiomas
◦ Monitoring tumour growth rate
◦ Evaluation in recurrence in the presence of scar formation (MRI non-
specific due to contrast enhancement of scar tissue)

Ga68 DOTATATE PET/CT is far superior to CT or MRI when there is low
lesion contrast (infiltrative lesions) or the imaging is prone to artefact
such as from base of skull

This study demonstrated that Ga-DOTATATE PET has
potential to improve planning contours with more precise
target delineation and as a consequence reduce treatment
toxicity for patients (OAR)

43
Q

What radiopharmaceuticals are used in prostate cancer

A

GA68 PSMA
F18 PSMA

44
Q

What is Ga68 PSMA

A

GA68 PSMA is the most commonly used
agent for prostate cancer imaging

We use this to image tumours with
increased prostate-specific-membrane-
antigen (PSMA)

45
Q

What is a PSMA

A

PSMA is a transmembrane protein primarily
present in all prostatic tissues

46
Q

Which malignancies have increased expression of PSMA

A

◦ Renal Cell Carcinoma
◦ Colorectal
◦ Prostate malignancy
◦ high PSMA expression on
the angiogenic neovasculature of solid
tumors (GBM)
◦ Adenoid Cystic Carcinoma

47
Q

When should GA68 PSMA be considered

A

 Primary staging in high-risk disease before surgical procedures or planning external beam radiation
◦ Gleason score >7, PSA > 20ng/mL, clinical stage T2c-3a)

 In this setting when the likelihood of lymph node or bony
disease is increased PSMA PET has shown to be superior to
CT, MRI or Bone Scans alone.

48
Q

What analogs should be utilised when PET imaging a glioblastoma

A

 PET using Amino Analogs have been proposed as a way to
provide prognosis and assess for tumour progression

49
Q

Epidemiology of Glioblastoma

A

 GBM account for 70% of gliomas
 1000 Australians affected annually
 Morbidity is devastating both physically and cognitively

50
Q

Benefits of PET Amino Acid Analog Imaging

A

Amino acid (AA) PET is promising in brain tumours
◦ The AA tracers show promise in distinguishing disease recurrence from pseudoprogression (an increase in the size of the primary tumor or the appearance of a new lesion followed by tumor regression)

AA transport is increased in malignant transformations due to cell
proliferation
◦ High tumour uptake and low background
◦ AA uptake may be present in non-enhancing sites of tumour
◦ AA are beneficial in demonstrating the site and extent of tumour
◦ May guide stereotactic biopsy or radiotherapy

51
Q

F18 and Ga68 half life and energy

A

511 keV
F18 - 110 min
Ga68 - 68 min

52
Q

Motion in PET effect on RT

A

Blurring in PET images can be used to RT advantage to define the GTV

53
Q

Application of F-FDOPA

A

Large neutral amino acids analogue that detects:
1. Glioblastoma
2. Parkinson’s disease
3. Congenital hyper insulinism

54
Q

Use of FMISO and FDOPA in RT

A

Use of radiosensitiers such as stereotactic boost to hypoxic regions

CSH059 Imaging (8 decks)

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