week 3-4 Flashcards
what are the 3 types of administration of radiotracers
- ingestion
- inhalation
- injection
what are the differences between NM and x-ray imaging
NM
- requires injection of radiopharmaceutical. the gamma ray emitted from the patient is detected by the cameras which creates images
X-ray
- images are formed by passing x-rays through the body to the image receptor placed behind the body
NM
- patient is radioactive
X-ray
- patient is not radioactive
NM
- provides functional information
X-ray
- provides anatomical information
NM
- gamma camera does not produce radiation
X-ray
- X-ray tube produces radiation
NM
- system/organ senstive
X-ray
- not system/organ sensitive
advantages of NM imaging
- non invasive and minimal risk to patients
- patient can be imaging over several hours without additional radiation dose
- provide qualitative information
- physiological changes take place before morphological changes
most common form on NM imaging
static/ planar acquisition
what is a static/ planar acquisition
- single shot
- study is completed either at the end of specified time or counts
what is a dynamic imaging
- study changes overtime
- imaging is undertaken while radiotracer is administered in a patient
- time per frame is dependent on the physiologic changes that is measured
- for purpose of imaging alone, longer time per frame are generally used in order to provide sufficient imaging statistics for each frame
what is whole body imaging
- move and shoot
- imaging of the whole body is acquired in one image
- continuous movement and imaging
- imaging time is dependent on the speed of the imaging couch
why is MUGA scan used
- imaging of a moving organ
- imaging the heart poses challenges due to the heart’s movement
- insufficient counts due to short acquisition time
- long acquisition time results in a blurred image due to overlapping of moving parts
- therefore, MUGA scan is used
- electrocardiographic (ECG) gating is used to synchronise image acquisition with the patient’s heart rate
factors that affect image quality
- collimators type
- distance of detectors to patient
- time per image
- photopeak selection
primary function of collimators
accurate spatial localisation
5 types of collimators
- low energy high resolution (LEHR)
- low energy general purpose (LEGP)
- medium energy general purpose (MEGP)
- high energy general purpose (HEGP)
- pinhole collimators
what is low energy collimators used for
nuclides emitting photons up to 160keV
what is medium energy collimators used for
nuclides emitting photos between 160keV to 250keV
what is high energy collimators used for
nuclides emitting photos >250keV
key artefacts in NM
- movement
- cold artefacts - seen as photophenic defects
- metallic implants, accessories, etc - hot artefacts - seen as areas of increased uptake
- injection site artefacts
- contamination artefacts
common indication for a bone scan
- skeletal metastatic disease and staging
- trauma/ fractures
- infection
- metabolic bone disease and other benign osteopathies (eg Paget’s disease, fibrous dysplasia)
- avascular necrosis
advantages of bone scan
- high sensitivity for cortical lesions
- ease of surveying the whole skeleton
disadvantages of bone scan
- non-specific
- any cause of increased metabolic activity whether due to metastatic disease, primary bone tumour, inflammation of trauma can cause increased tracer uptake
explain the bone scan uptake mechanism
- diphosphonate is absorbed onto the surface of bone especially at sites of new bone formation
- uptake will depend on local vascularity and the degree of osteoblastic activity
patient preparation for a bone scan
- ensure patient well hydrated and void frequently
- void before scan
- remove all metal objects before imaging
- note location of pacemaker, colostomy bag etc
why must patients hydrate themselves for bone scan
- allow rapid excretion of radiopharmaceutical via kidneys
- minimise radiation dose to bladder
- pubic lesions may be obscured by bladder activity
- to obtain good quality image
what is the average injection-to-imaging time
2-4 hours
patient positioning for a bone scan
- supine
- elbows straight with palms on lateral side of thighs
3 phases in a triphasic bone scan
- phase 1: angiographic/ flow
- phase 2: blood pool
- phase 3: delayed
