RNI gamma camera equipment worksheet Flashcards
- What are the THREE main branches of RNI and what types of radionuclides do they use?
a. Radionuclide Imaging (RNI) - Diagnostic Imaging
i. It uses a diagnostic gamma camera and mainly using 99mTc (gamma emitters)
b. Radiotherapy RNI - the use of RT radionuclides to treat cancers/clinical conditions
i. using β- emitters (can also image them in some cases)
ii. It uses tracers which emit β- emission
- we can image an examination that uses iodine or radioactive iodine, particularly Iodine-131, which is a beta emitter but also emits 5 gamma rays as well as part of its radioactive decay
c. Positron Emission Tomography (PET) combined with CT (PET/CT)
i. PET uses different radionuclides. These use pair production. So the gamma photons produce as a result of pair production, are much higher value. So they wont be detected by a gamma camera.
- State TWO advantages to RNI imaging
- Able to assess physiology and function that cannot be assessed with other modalities
- Relatively low dose in comparison to other modalities
- Can assess function as a whole
- Ability to do 3D images when combined with CT (PET/CT and SPECT)
- Addition of anatomical imaging - CT/MRI
- State TWO disadvantages to RNI imaging and how are these rectified?
- Poor resolution - Therefore, alternate modalities may be needed to clarify.
- High sensitivity, poor specificity (it can say something is wrong but can’t always tell you with absolute certainty what it is).
- It can take a long time to get to the target tissue - challenging for paediatric patients to stay still
- dependent on the availability of radiopharmaceuticals
- Describe the imaging process of a gamma camera from patient to resultant image.
- Initially, radiopharmaceutical is injected into the patient’s arm.
- Once radiopharmaceutical is administered to the patient, they become the radioactive source and gamma photons is emitted from patient in all directions.
- However, only those gamma photons that are perpendicular (at a right angles) to the camera will manage to pass through the holes of the collimator and get to interact with the sodium iodide (with thallium) (NaI[TI)] scintillating crystal, while scattered photons will get absorbed by the collimators.
-Collimators determine the resolution of the image.
4. Gamma photons then interacts with the NaI (TI) scintillating crystals and produces light. The intensity of the light is proportional to the gamma photon energy.
If a scattered gamma photon managed to get through, it will have less energy and it will produce less light (less bright). Scatter gamma photon affects the image quality as it produces noisy image.
5. The light is detected by the photomultiplier tube. The light gets multiplied and converted into a current (electrical signal) which plots the X & Y coordinates in the image matrix.
6. Pulse Height Analyser (PHA) - acts like a filter.
It measures the energy value of gamma photons to make sure they are the correct energy and gets rid of scattered energy.
If the energy value is correct, it gets mapped on the image matrix.
5. Define the following collimators stating their energy range and state a radionuclide that can be used for each: LEAP MEAP HEAP LEUHR
a. LEAP - (Low energy all purpose) Low energy (less than 150 keV) Radionuclides: 1. 99mTc (Technetium) 2. 201Tl (Thallium) 3. 123I (Iodine) b. MEAP- (Medium energy all purpose) - Medium energy (less than 375 keV) Radionuclides: 1. 111In (Indium) 2. 67Ga (Gallium) radionuclides 3. Might use in radiotherapy department for diagnostic purposes for infection purposes or particular tumour types c. HEAP- (High energy all purpose) - High energy (less than 500 keV) Radionuclides: 1. 131I (Iodine) 2. Usually used in thyroid ablasions 3. Interested in sensitivity d. LEUHR - (Low energy ultra high resolution) - bone imaging Low energy (less than 150 keV) Radionuclides: 1. 99mTc (Technetium) 2. 201Tl (Thallium) 123I (Iodine)
- State FIVE requirements of a scintillation crystal in a gamma camera
- The front face and sides are coated with a thin layer of aluminium to make it air-tight and light proof
- Good absorber of radiation
- Good converter of absorbed energy to produce light flashes
- Sensitive to rapid temperature changes
- (no more than 3degrees per hour or the crystal will crack) (has to have air-conditioned room) - Efficient converter of absorbed energy
- Why is it important to have an air conditioned room in RNI?
It is important to have an air conditioned room in RNI because it will prevent the crystal from cracking due to rapid temperature changes.
- Describe how a photomultiplier tube works in converting light to a signal.
- The light produced from the scintillating crystal is guided into the photocathode which releases electrons which are then proportional to the amount of light that it received from the crystal. Therefore, the more light received, the more electrons there is.
- The electrons are directed towards a dynode and every time it hits a dynode, it encourages more electrons to be released each time.
- The potential difference between the photocathode and the dynode attracts the electrons and accelerates them. As a result, more electrons are released at the dynode. Another potential difference is applied at the next dynode and the same process repeats until it reaches the anode.
- once it reaches the anode, it’s got 1000x the signal from the original one that was directed to. These signals will plots the X & Y coordinates in the image matrix.
- What is the purpose of the Pulse Height Analyser (PHA)?
PHA acts as a filter by excluding background and scatter radiation or gamma photons that is not within the desired range so it does go through to get more accurate plotting of photons on the image matrix.
- What is meant by the term dual energy acquisition and how does the PHA allow this?
Dual energy acquisition is when we utilise two radionuclides at the same time. An example of that is a VQ scan when they want to see perfusion and ventilation.
Two radionuclides will be used for that.
- Describe how a SPECT (Single Photon Emission Computed Tomography) image is acquired
- Everything is the same as how a gamma camera acquires images.
- The only difference is the camera acquires static images at 3 degree orbits around the patient until it reaches 180 or 360 degree rotation depending on the examination.
- The length of the scan is dependent on how many camera heads there is.
- A patient arrives in department for Bone Scan and are injected with 600MBq of 99mTc-MDP. What advice do you give to the patient prior to them leaving the department to maximise the quality of the scan in 3 hours’ time when the patient returns to be imaged and to ensure radiation safety?
- Patients must drink 2 pints of fluid over the 3 hours
- flush the chain twice when they void their bladders.
- Males are asked to sit down on the toilet and avoid urinals to prevent radioactive from splashing in the toilet.
- Avoid public transport.
- No close contact with pregnant women and children for extended periods.
- Women who are breast feeding are encouraged to express their milk before they have the injection of radionuclide.
- In patients with catheter bags, must have their bags labelled
- Two bone patients in a waiting room constitute a controlled area in RNI (where the dose is likely to exceed 800MBq of activity) - other people should not be in that vicinity
- Why is it important to record the absolute injected dose in functional RNI imaging and how is this done?
- Absolute injected dose required for quantification. This is to accurately gauge or to quantify differential function between both kidneys.
- Post injection, any residue left in the syringe must be calculated to find absolute dose injected.
- (residual syringe dose is subjected to original dose)
- At what dose does a patient have to be isolated due to be a controlled area?
800 MBq
- 2 bone patients in a waiting room constitute a controlled area in RNI
- where the dose is likely to exceed 800MBq of activity - other people should not be in that vicinity
- State FOUR common SPECT procedures naming the radiopharmaceutical used for each.
• The commonest at top:
1. DMSA for cortical scarring = 99mTc
2. 99mTc-MDP: bone diseases, cancer metastatic to bone
3. Brain SPECT ( brain perfusion) = 99mTc-HMPAO, 99mTc-ECD
4. Stress/Rest Myocardial Perfusion Imaging of CAD =
• Stress: 99mTc-sestaMIBI or 99mTc-Tetrafosmin
• Rest: 99mTc-labeled agents or 201Tl chloride
• (only half if stress/rest is given without the correct radionuclides/radiopharmaceutical)
