1. Basics of Medical Imaging Flashcards
What are the types of clinical imaging?
- transmission imaging
- reflection imaging
- emission imaging
What are the transmission imaging modalities?
- X-ray modalities: radiographs, mammography, fluorosopy, CT
- a beam of high energy photons is passed through the body and they are either attenuated or blocked
What are the reflection imaging modalities?
- reflection of sound waves by the tissues
- ultrasonography (w/ doppler function), sonoelastography
What are the emission imaging modalities?
- nuclear medicine: gamma/positron emission from radioisotopes
- MRI: radiofrequency signal emission from hydrogen atoms
What is spatial resolution?
- it is the measure of the ability to differentiate objects from one another on imaging, when objects are in close proximity (measured in line pairs per mm, lp/mm)
- CT spatial resolution can be enhance by HRCT
- spatial resolution of nuclear medicine in relatively poor
- submillimeter-sized microcalicifications can be detected by excellent spatial resolution on radiographs
What is contrast resolution?
- ability to differentiate between different intensities on an image
- radiography differentiates 5 principle densities: metal, bone, water, fat and air
- MR has excellent soft tissue resolution
- contrast agents are used to enhance the contrast resolution
What are contrast agents?
- a substance used to increase contrast resolution in medical imaging
- different forms of contrast agents that can also be administered differently according to the substance
- each modality has contrast agents specific to it
What is the terminology for describing a radiograph?
- darker structures have low attenuation and more lucency – increased transparency or radiolucent
- brighter structures have high attenuation and more opacity – decreased transparency or radiopaque
What is the terminology for describing CT images?
- hypodense: dark structures with low attenuation
- moderate density
- hyperdense: brighter structures with high attenuation
What is the terminology used to describe US images?
- anechoic: appears black
- hypoechoic: appears dark
- hyperechoic: appears bright
- echodense: appears white
What is terminology used to describe MR images?
- hypointense: low signal intensity, appears darker
- intermediate signal intensity
- hyperintense: high signal intensity, appears bright
What is the terminology used to describe nuclear medicine images?
- low radiopharmacon uptake: appears dark
- high radiopharmacon uptake: appears brighter
What are the types of ionizing radiation?
- X-rays
- mammography
- fluoroscopy
- computed tomography
- nuclear medicine
What are the types of non-ionizing radiation?
- ultrasonography
- magnetic resonance imaging
What are the hazards of ionizing radiation?
- EM emissions with sufficient energy can result in the formation of free radicals in the body, which are highly reactive
- annual radiation dose from natural sources is 2.5 mSv/year
- ALARA principle is important to minimize hazards
What to consider in choosing the most ideal modality?
- spatial resolution
- contrast resolution
- depth of penetration
- artefacts
- speed of acquisition
- summation
- ionizing radiation
- contraindications
- cost
- availability
What are the major strengths of radiography?
- fast
- available
- great spatial resolution
What are the major strengths of fluoroscopy (and DSA)?
- functional information
- real-time imaging
- therapeutic intervention
What are the major strengths of CT?
- fast
- 3D imaging
- available
- multiple regions can be examined in short time
What are the major strengths of US?
- no ionizing radiation
- available (point-of-care)
- cheap
- real-time imaging
- no contraindications
- contrast enhanced US
What are the major strengths of MRI?
- no ionizing radiation
- 3D
- great contrast resolution
- angiography w/o contrast
What are the major strengths of nuclear medicine?
- functional information
- early detection
What is the patient preparation for interventional radiology procedures?
- INR and platelets testing (in moderate/high risk procedures)
- minimum 4 hour fasting before procedure
What is the patient preparation for US?
- minimum 6 hour fasting for abdominal US
- moderately full urinary bladder for pelvic US
- no special preparation for contrast enhanced US
