Hybrid Imaging (PET Equipment and Clinical Applications) WORKSHEET Flashcards
What types of radionuclides are used in PET imaging and what types of energy do they
produce (and which are detected by the PET scanner)?
They use positron emitting radionuclides as a result of pair production. This
electron-positron pair annihilate each other as positrons and negative electrons cant
co-exist , therefore this produces 2 gamma photons which move at 180 o to each
other and have the energy of 511 KeV (the pair production radionuclide must have
an energy of 1.02 MeV)
Example of this is Fluorine-18, Carbon-11
State TWO advantages to PET/CT imaging
CT has highest resolution and low noise Physiologic PET image is perfectly aligned
with a high resolution scan (CT)
Combination of functionality and anatomy means better diagnostic imaging
It’s good for radiotherapy, as it reduces unnecessary radiobiological damage to
healthy tissues image to reduces the treatment areas to just active diseases reduces
normal cell radiation burden radiotherapy cell damage from radiotherapy,
usage for monitoring response to treatment plan, by just using CT you are not able
to see changes as well as pet/CT scan you can see the flair (uptake of fluorine)
decreasing/increasing
i.e. useful for determine what to do next with chemo patients
non-invasive and painless (only invasion is injecting radionuclide into patient)
Certain radionuclides are specific to certain tumour types, so if you see it as a
hotspot on the screen you can identify the tumour type.
Integrated system there = cost effective
The CT is very fast and can be used for the Attenuation Correction.
Avoidance of unnecessary surgery
State TWO disadvantages to PET/CT imaging and how are these rectified?
Diabetic patient who undergo pet/ct scan must do so under precaution. The
radioactive material is combined with glucose and injected into patients, this can
affect diabetic patients (hyperglycaemia) a diabetic patient’s blood sugar level will be
Imaging Science Principles Module 2021-22
evaluated, and a glucose serum blood test might be administered. This can significantly
increase the time required to complete the testing.
PET/CT uses high energy gamma photons hence more risk than nuclear med exam,
as a result patient should be in a controlled area
Risk to pregnant woman, however there’s always risk therefore benefit should
outweigh the risks
Pregnant oncology patient poses A LOT of risks and ethical considerations regarding
treatment plan. Also have to respect mothers issues
Radionuclides are costly to produce and manufacture Cost comes from the expense
of producing the short-life isotopes and transporting them.
Have stringent QA requirements if these fail must cancelled and re-booked
Relatively HIGH DOSE, combination of the two means you are factoring in both
doses (however under i(re)mer patients can receive high dose as long as there is
justification
Describe the imaging process of a PET/CT scanner from patient to resultant image.
Patient lies down the bed they first have their CT scanogram done.
Then they have a full body CT scan where CT attenuation correction is done by
working out the body thickness of different parts this adds to our PET scan.
CT attenuation correction improves the quality of the image, using reconstruction
algorithms
this fuses the CT AND PET IMAGE TOGETHER.
You get a CT image, PET image and then the COMBINED PET/CT IMAGE
PET IMAGING:
This circular gantry is surrounded with an array of scintillation crystals grouped in 4’s
Each crystal has their own integrated system they have their own photomultiplier
and signal circuitry which processes the data centrally
The gamma photons emitted by the patient is absorbed by the scintillation crystals
in the detector, this then produces light
This is detected by the photomultipliers (increases signal)
Information is sent to the Coincidence processing unit
Computer plots back to where this energy is coming from
Through coincidental scanning and attenuation of the CT, you can see where in the
body these gamma photons were emitted
If there is more events occurring this means that the body Is taking the FDG up more
meaning there will be more hotspots on the resultant image
The PET scan detects the energy emitted by positively charged particles (positron) as the
radiotracer breaks down In the patient body, positron are made. The energy appears as 3D
image on the computer.
Describe how a SPECT (Single Photon Emission Computed Tomography) image is acquired
and what are the advantages of combining this with CT in SPECT/CT imaging.
To acquire SPECT images, the gamma camera acquires static images as it is rotated
around the patient.
Projections are acquired are defined points during the rotation
Typically at 3 degrees
Imaging Science Principles Module 2021-22
A 360degree rotation is used to obtain optimal reconstruction
180degrees if you have two gamma camera heads
To either 180 o or 360 o depending on the exam
Data is built into a 3-D image which can be sliced through coronal, sagittal and
transverse planes
By combing it with CT you integrate the high resolution from CT to give functional
anatomy to get better diagnostic imaging
• The CT is very fast and can be used for the Attenuation Correction.
Describe why it is necessary to use CT to correct attenuation in a PET scan.
The 511 KeV gamma photons when being emitted from the patients body
encounter different tissue types before they get absorbed by the scintillation
crystals
So CT is just compensating for those differences IN BODY THICKNESS where the
events may be occurring, this can alter the photon energy slightly
the image is sharper and more accurate giving us better diagnostic images
State FIVE factors that can affect attenuation correction when using CT with PET imaging?
Need to adjust attenuation maps from CT kV to 511keV (to mirror PET)
(see graph)
uses Ct Hounsfield units to correspond to density and then look at energy ranges
PET produces and compares them knowing that at this energy Pet energy should be
like this (uses table) because that’s the attenuation correction factor. Applies certain
algorithm to that specific point and that will change the way that it appears on actual
pixels on my screen
Contrast media (has high atomic number affects the photons)
Metal objects/artefacts/implants
Movement
Cardiac
Breathing
Bed stability (if it wobbles or moves then this causes issues)
- With regards to PET/CT imaging (Case study type question):
Imaging Science Principles Module 2021-22
A patient arrives in department for PET scan and are injected with 250MBq of 18 FDG. She is a
breast feeding mother and has come with her partner for the scan
What checks should you make prior to injecting them with the PET radionuclide.
No smoking, as smoking impacts the way FDG travels around the patients body
Patient should not exercise vigoursly a day before the scan to reduce the metabolic
activity of muscle, if muscle activity is high then it will absorb all the FDG, resulting in a
poor image as all you see is muscle.
If patient is diabetic need to consider this (i.e glucose monitoring), can be prevalent as
she is a breat feeding mother and post-partum diabetes is common side effect of
pregnancy. Glucose test has been done
Since the mother is breast feeding I would tell patient they are able express milk prior to
the FDG being injected, as it is advised mother should not be in close contact with baby
up to 4hrs after examination and third party should potentially feed the baby due to the
radiation risks to baby
PATIENT SHOULD LIE IN REST AREA for some time TO MAKE SURE THEY ARE RELAXED (IF
THEY ARE NOT RELXAED CAN AFFECT FDG UPATKE AND ALTER RESULTS)
Empty bladder before scan. TO REMOVE ANY UPTAKE IN BLADDER, patient has to lay
down for a while after the scan and having a full bladder is not ideal
D13 CHECKS (THIS IS MORE ABOUT PATIENT RATHER THAN LINKED TO ISP)
NAME
DATE OF BIRTH
ADDRESS
IN LINE WITH IRMER REGULATIONS
PATINET SHOULD BE IN A GOWN, NO METAL ON THE PATIENT (AFFECTS CT IMAGE AND
CAUSES ATTENUATION PROBLEMS)
That baby was fed by mother prior to the FDG being administered
FDG concentration in breast milk is low, we have to consider radiaition dose to baby as
they would be in close proximity with the mother
Baby is more radiosensitive, advised that baby is fed by third party up to 4hrs after
injection to reduce radiation burn to baby
What advice do you give the patient post injection and what are the implications of this if this advice
is not followed in terms of image quality and radionuclide up-take.
Patient should relax for 45-60 minutes post injection, and they must stay isolated in their
own cubicle until scan and cannot leave the department
Patient should try to stay as still as possible should not speak, or chew anything as this can
increased FDG uptake in these areas therefore altering the results
Patient should NOT MOVE, as movement increases the FDG to those muscles involved
MOVEMENT AFFECTS THE IMAGE QUALITY, as it can mask pathology because there’s an
increased fluorine uptake to those areas
Imaging Science Principles Module 2021-22
If this advice is not followed it will skew the results as there will be false positives results, false
uptakes. Uptake in muscles means it will overshadow any pathology.
uptakes. Uptake in muscles means it will overshadow any pathology.
You go to get the patient after an hour and find that their patient gown is wet with urine. The
patient is very embarrassed and says that she has had difficulties since a difficult child birth. What
steps do you follow to deal with this situation?
Priority in how to deal with is patient first, radiographer (staff members) next and then room
If radiographer was not wearing gloves they have been contaminated by radioactive urine,
therefore another staff member should come help. Need to raise alarm
This is a radioactive spill and minimising risk to everyone should be the priority
Person dealing with this must be wearing protective equipment, aprons, gloves etc
First get the patient changed, do this by getting patient to stand in a yellow bag and remove
all clothes, must give a fresh gown to cover dignity
Get towels and pat the patient dry
Then we must scan patient to see how radioactive they are
Assess the situation with a dosimeter, must see where the urine has spilled to and mark
these areas with tape to know where the extent of spread is
Geiger counter is important
The yellow bag SHOULD BE LABELLED WITH WHAT TYPE OF RADIONUCLIDE, DATE AND TIME
and be stored in the radiation bunker until safe to dispose
Patient is then taken to get a shower
Wash all contaminated areas with soap and water, be as gentle as possible so as to not rub
radioactive substance into open wounds or the eyes
DECON90(2%) HOT AREAS prior to taking a shower
Continue washing until with Decon90 and showering until patient has reached safe levels
The room should be mopped moving from outside-inwards and scrub area with decon90 and
keep monitoring the levels
FILL OUT INCIDENT REPORT, HAVE TO INFORM RPS
What are the implications for the scan itself in this case?
IMAGES BECOME UNDIAGNOSTIC AND NEED TO REPEAT SCAN HENCE RESCHEDULED,
DECONTAMINATION PROCESS MEANS WE MAY HAVE LOST THE HALF LIFE due to decay,
RE-BOOK ANOTHER DAY AND ANOTHER INJECTION.
This is deemed as an unnecessary radiation dose to patient therefore must carry risk
assessment to see the implications it has on the patient.
