week 5-6 Flashcards
1
Q
advantage of SPECT
A
- improved image contrast
- absolute 3D localisation of tracer distribution
2
Q
maximum COR error
A
<0.5 pixels
3
Q
application of NM cardiac imaging
A
- MUGA
- cardiac amyloidosis (PYP imaging)
- SPECT myocardial perfusion imaging
- PET/CT cardiac imaging (MPI and viability imaging)
- cardiac sarcoidosis (18F-FDG PET/CT)
4
Q
what is NM cardiac imaging
A
- non invasive evaluation of cardiac physiology and function
- selective detection and functional consequences of numerous cardiac abnormalities
- provides complementary information to anatomic imaging techniques
5
Q
radionuclide imaging procedures are designed to assess
A
- myocardial perfusion and viability
- regional and global ventricular function
6
Q
what is ECG G-SPECT
A
- semi quantitative evaluation of coronary perfusion and LV function
7
Q
semiconductors detectors possess superior
A
- energy resolution
- better scatter rejection
- can be made in a compact
- and rugged package
8
Q
with superior characteristics, semiconductor detectors ensure
A
- improved image contrast
- improved multi-isotope imaging
- faster scanning/ lower dose scans
- more flexibility in scanner design
9
Q
what is SPECT/CT
A
- hybrid imaging technique that allows the direct fusion of morphologic information and functional information
- lesions visualised by functional imaging can be correlated with anatomic structures
- more anatomic information = increase sensitivity and specificity or scintigraphic findings
- add true diagnostic information derived from CT imaging
10
Q
advantages of SPECT/CT
A
- improved attenuation correction, resulting form the more accurate and precise attenuation map with CT
- add value to SPECT studies with superior quantification of radiotracer uptake
- ability to perform complementary diagnostic studies in the same setting
11
Q
challenges associated with SPECT/CT
A
- increased cost of the equipment and room preparation
- patient motion, CT metal artifacts
- total radiation burden to patient
12
Q
PET imaging is useful in
A
- measuring blood flow into tissues and tumours
- imaging and measuring receptors
- imaging of enzyme and cellular functions
13
Q
isotopes elements used for PET
A
- carbon 11
- oxygen 15
- fluorine 18
14
Q
why do PET scan
A
- higher sensitivity
- uniform high resolution
- superior attenuation correction
- superior quantification
- high clinical sensitivity and specificity
15
Q
PET decays and emits
A
positron
16
Q
in PET, protons decay to
A
a neutron, positron and neutrino
17
Q
daughter isotope in PET has how many more/less atomic number than parent
A
one less
18
Q
in PET, what happens to the positrons emitted
A
annihilate nearby electron, resulting in 2 gamma rays of 511KeV travelling at 180deg to each other
19
Q
what is “coincident”
A
two detection events unambiguously occuring within a certain time window
20
Q
resulting image of a PET scan shows
A
- tracer distribution throughout the body of the subject
- 3D images of the localisation of the radioisotope can be reconstructed
21
Q
design of the detector block in a PET/CT scanner machine
A
- a block of LSO crystals is coupled to 4 small PMT with light sensitive adhesive
- each block is magnetically shielded by a metal casing
- grooves between adjacent crystal blocks are filled with light reflecting compound
- 12 blocks arranged in a 3x4 format constitute a bucket
- 12 buckets (144 blocks) in the whole PET ring
22
Q
advantages of electronic collimation
A
- improved sensitivity
- improved uniformity
of the point source response function
23
Q
3 types of coincidence events
A
- true
- scattered
- random
24
Q
what is true coincidence
A
- when both photos from an annihilation events are detected by detectors in coincidence
25
what is scattered coincidence
at least one of the detected photons has undergone at least one compton scattering event prior to detection
26
what is random coincidence
two photos not arising from the same annihilation event are incident on the detectors within the same coincidence time window of the system
27
what are the energy of the different coincidence
T = 511kev
S = <511 kev
R = 511 kev
attenuated / undetected = <511kev
28
what is scatter map used for
correct the PET scan
29
problem associated with attenuation in PET scan
- photons are stopped in the patient body reaching the PET detector
30
consequence of attenuation in PET scan
- reduces appearance of deep lesions
- reduces quantitative accuracy
31
solution to attenuation in PET scan
- perform attenuation correction with scan of patient
32
problems with random coincidence
- randoms equal and may exceed true events
33
consequence of random events
- reduced contrast
- reduced accuracy
34
solution to random events
- measure random events
- reduce randoms by decreasing coincidence time window
35
key benefits of PET/CT
- combine functional and anatomical imaging for highest accuracy coregistration and fusion
- PET and CT components can be operated independently
- short duration, low noise CT-based attenuation correction and scatter correction
- faster overall scanning time
- fully quantitative, whole-body images for SUV calculation
- applications in improved disease localisation, biopsy guidance, therapy monitoring, and radiation therapy planning
36
imaging sequence for a PET/CT
- topogram or scout for positioning
- spiral CT scan and generation of ACF
- PET scan over the same axial range as CT + reconstruction of CT images simultaneously
- attenuation correction of PET data
- reconstruction of attenuation corrected PET data
- display of final fused images
37
why PET/MR
- high soft-tissue contrast
- advanced MRI techniques such as MR spectroscopy allows in vivo identification of specific chemical compounds and provides insight into physiological changes in tissue of interest
- combination of PET and MRI increases the diagnostic accuracy but PET and MRI data fused in retrospect often result in misalignment and motion artefacts
- simultaneous acquisition can be achieved; risk of misalignment due to patient movement will be greatly reduced with shorter examination time
38
advantages of PET/MR
- reduce exposure to ioninsing radiation
- similar to image quality and quantitative data achieved using PET/CT
- higher quantitative lesion contrast due to decrease in background SUVs
- volumetric axial sequences gives good resolution and better registration
39
steps involved in reconstruction of SPECT image
1. acquisition
2. correction
3. QC
4. reconstruction (filtered back projection)
5. attenuation correction
5. reconstruction (transverse --> coronal and sagittal)
40
centre of rotation calibration recommendation
- point source placed at the centre of the FOV
- point source placed off centre relative to the AOR
- line source
- byte or word mode of acquisition
- separate COR calibration for 64x64 and 128x128 matrix sizes
41
radionuclide imaging procedures are designed to assess
- myocardial perfusion and viability
- regional and global ventricular function
42
regional wall motion abnormalities are classified into
- hypokinetic - diminished wall motion
- akinetic - absent wall motion
- dyskinetic - particular segments moves paradoxically outward rather than contracting inward during systole
43
what is the difference between cardiac SPECT and conventional SPECT
- use of CZT, which have a higher sensitivity for the detection of photons
- advanced software solutions, such as iterative reconstruction, resolution recovery and noise reduction
- reduction in the administered activity while maintaining image quality
44
2 dedicated cardiac SPECT
- CZT with multiple single-hole detectors
- upright CZT camera with sweeping parallel-hole collimators
45
difference between administered dose in conventional and dedicated cardiac SPECT
C = 8-12mCi
D = 4-6mCi
46
acquisition duration for conventional and dedicated SPECT
C = 15-25mins
D = 2-8 mins
47
what does MUGA do
- qualitative and quantitative of LV function
- assess cardiac chamber morphology
- evaluate global and regional measures of ventricular function
48
indications for a MUGA scan
- cardio-oncology
- vavular heart disease
- cardiomyopathy
49
what is the radiopharmaceutical used for MUGA
- Tc99m labelled RBC
- reduction of Tc99m pertechnetate is required to bind firmly to haemoglobin
50
radioactivity for MUGA radiotracer
20mCi
51
RBC labelling techniques
- in vivo
- in vitro
- mixed in vivo/ in vitro
52
indications for PYP
- individuals with heart failure and unexplained increase in LV wall thickness
- individual over the age of 60 years with unexplained heart failure with preserved ejection fraction
- individuals with unexplained neuropathy, bilateral CTS or atrial arrhythmias in the absence of usual risk factors, and S&S or heart failure
- diagnosis of cardiac ATTR in individuals with CMR or echocardiography consistent with cardiac amyloidosis
- patients with suspected cardiac ATTR amyloidosis and contraindications to CMR such as renal insufficiency or any implantable cardiac device
53
additional imaging to PYP
- SPECT
- whole body planar imaging
54
limitations of PYP
- high affinity for areas of bones with altered osteogensis, damaged myocardial cells and RBC, specifically visualised in areas of blood pooling
- uptake by overlying breast tissue, degenerative bone disease, parenchymal lung processes such as consolidation and atelectasis, and attenuation from overlying devices on the chest wall can all result in false-positive when using planar imaging alone
55
indications for SPECT MPI
- ischemic assessment
- risk stratification in stable CAD
- post-acute MI eval
- eval after revascularisation procedures
- pre-operative assessment
- viability assessment to detect hypoxic yet viable myocardium that would benefit from revascularisation
56
pharmacologic stress agents for stress testing in SPECT MPI
- dipridamole
- adenosine
- regadenoson
- dobutamine
57
advantages of SPECT MPI
- lower cost
- less complex
- better accessibility and availability
58
advantages of PET/CT MPI
- shorter imaging protocol
- lower radiation exposure
- ability quantify absolute myocardial perfusion
59
radiotracers for PET/CT MPI
13NH3
82Rb
15O water
60
purpose of myocardial viability imaging
- identify chronically dysfunctional myocardium in CAD that may benefit from revascularisation
- performed as a combination of MPI and FGD
61
FGD PET/CT is a useful imaging method for
- diagnosis and monitoring treatment response in patients with cardiac sacroidosis
- detection of early disease, determining active vs chronic disease
- combined whole-body PET examination performed for the detection of systemic sarcoidosis
62
imaging protocol for sarcoidosis
- FDG PET/CT performed with resting MPI, followed by whole body imaging to assess for extra-cardiac disease
- high fat and low carbs diet followed by prolonged fasting of about 12-18 hours has been recommended to suppress normal metabolic uptake of FDG in the myocardium so that FDG accumulation due to sarcoidosis can be detected
63
what is the gastric emptying scan for
- evaluate the rate of gastric emptying
- involves eating a light meal that contains a small amount of radioactive material
- goal of scan is to identify patients with gastric motility problems who will benefit from either prokinetic drugs or other treatments to alleviate their symptoms
- amount of radioactivity in stomach is measured at various time points, to determine the volume of a meal remaining in stomach and thus determine the rate of GE
64
indications of GE scan
- exclude gastroparesis as a cause for persistent nausea and vomiting
- confirm or exclude delayed gastric emptying in diabetic patients w poor glycaemic control
65
contraindications of GE scan
- allergies to the recommended meal
- hyperglycemia in diabetic patients
66
advantages of GE scintigraphy
- non invasive
- quantification of the data
- low radiation burden permitting repetitive testing
- ability to analyse fundal, antral, and overall gastric motility
67
patient position during GE imaging
erect, hands resting on top of detectors
68
how many times is GE scan imaged and at what time points
4 times
- 0h
- 1h
- 2h
- 4h
69
what is considered normal GE
- 30 to 60% gastric retention at 2 hours and
- 0 to 10% at 4 hours
70
what is considered delayed GE
- more than 60% gastric retention at 2 hours or
- more than 10% at 4 hours
71
what is rapid GE
less than 30% gastric retention at 1h
72
what does 0-2hrs see in GE
early phase - reflect primarily fundal function
73
what does 2-4 hours see in GE
late phase - reflect how antral process and push food into the duodenum
74
advantages of hybrid imaging
- increased diagnostic accuracy
- better treatment planning
- reduced need for additional tests
- earlier detection of disease
- more personalised treatment
- improved guidance for interventions
75
contraindication for a GE scan
pregnancy
76
PMTs have very large
electronic gains (10^6) with relatively low noise
77
PMTs have conversion efficiency of
20% - affects both energy resolution and intrinsic spatial resolution
78
PMTs are affected by
environmental changes such as
- temperature
- humidity
- magnetic fields and
- their age
79
examples of improved replacements for conventional PMTs
- position sensitive PMT (PSPMT)
- avalanche photodiode (APD)
- silicon PMT
80
radiotracer used in MUGA
Tc-99m labelled RBC
81
radiotracer used in SPECT MPI
Tc-99m
Thallium-201
82
radiotracer used in PET/CT MPI
ammonia
rhubidium
water
83
radiotracer used in PET/CT viability imaging
18F-FDG
84
radiotracer used in PYP imaging
Tc99m-PYP
85
radiotracer used for cardiac sarcoidosis imaging
18F-FDG PET/CT
