Lecture 3 & 4: An introduction to medical imaging & Radiology Flashcards
How do X-rays work?
- Focused bean of high energy electrons pass through body onto receiver
- Some are absorbed or scattered
- More dense = higher attenuation = lighter appearance
What are the advantages of using X-rays?
- Quick
- Portable
- Cheap
- Simple
What are the disadvantages of using X-rays?
- Radiation (relatively low but still present)
- One plane = 2 dimensional
- Poor soft tissue imaging
What are some clinical examples that X-rays can be used for?
- Chest: infection, oedema
- Bowel: dilation, perforation
- Orthopaedic: fracture / trauma
- Post-procedure: Nasogastric rube, pacemaker
- Dentistry
How does ultrasound scanning work?
- High frequency sound waves are sent into the tissue
- Depending on the composition of different tissues, signal will be returned back at separate intervals
- Detected by scanner
- Creates electrical signal (time taken to come back = how deep a structure is, proportion of reflected waves = density of structure)
What are the advantages of using ultrasound scanning?
- Studies function of moving structure in real-time
- Emits no ionizing radiation
- Relatively inexpensive
- Quick to perform
- Portable
- Can be inserted into body cavities
What are the disadvantages of using ultrasound scanning?
- Very operator defendant- depends on how well the person uses it and how well they know their anatomy
What are some clinical examples that ultrasound scanning can be used for?
- Imaging the fetus in pregnant women
- Elastography (determines whether a tissue is hard or soft indicating the presence or absence of disease as tumors are harder than surrounding tissue)
How does medical resonance imaging work?
- Strong magnetic field aligns hydrogen atoms
- Some point towards head and some towards feet
- Radiofrequency pulse applied
- Unmatched ions absorb energy and spin in other way
- Pulse turned off and atoms spin returns which emits energy
- Computer processing to generate image
What are the advantages of medical resonance imaging?
- No radiation
- Excellent soft-tissue contrast
- Different pulse sequences can be used for specific MRI diagnostic imaging
What are the disadvantages of medical resonance imaging?
- Health risks associated with tissue heating from exposure to the RF field can become non-functional
- Metal implanted devices will accelerate to great speeds
- More expensive
- Time-consuming
- Claustrophobia-exacerbating
- Clinically obese patients cannot fit
- Loud
What are some clinical examples that medical resonance scanning can be used for?
- Detecting disease in various organs (liver, breast, pancreas)
- Assessing effects of vascular disruption agents on cancer tumor survival
- Provides superior information as compared to CT scans when seeking information about headaches
How do CT scans work?
- X-ray tube opposite a detector in a ring-shaped apparatus rotate around a patient
- Produces computer-generated cross-sectional image
What are the advantages of using CT scans?
- Quick
- Good spatial resolution (easy to distinguish between adjacent tissues)
- Can scan most areas
What are the disadvantages of using CT scans?
- Health hazards due to significantly more ionizing radiation than a radiograph
- Lower contrast resolution (hard to distinguish between different densities within the same tissue)
- Requires breath holding
- Incidental findings
- Overuse (fishing for diagnosis)
What are some clinical examples that CT scanning can be used for?
- Diagnosis: cancer, stroke, bone injury, blood flow
- Guide further tests or treatment: radiotherapy,biopsy
- Monitor conditions: cancer treatment
How does positron emission tomography work?
- Radionuclides bound to glucose (places that are metabolically active)
- PET camera detects annihilations (high energy gamma rays) from areas of high glucose metabolism
What are the advantages of PET scans?
- Non-invasive diagnosis and patient management
What are the disadvantages of PET scans?
- Health hazards due to radiation
What are some clinical examples that PET scans can be used for?
- Images of radioactivity distribution throughout the body can show rapidly growing tissue, like tumors, metastasis or infection
How does fluoroscopy work?
- Radiocontrast agents are administered into patient
- Radiocontrast agents strongly absorb or scatter X-rays and in conjunction with real-time imaging, allow demonstration of dynamic process
- Enhanced by contrast
What are the advantages of using fluoroscopy?
- Real-time imaging
- Cheap
- Interventional procedures can be conducted
What are the disadvantages of fluoroscopy?
- Health hazards due to radiation
What are some clinical examples that fluoroscopy can be used for?
- Angiography: examination of blood vessels
- Contrast GI studies
- Therapeutic joint injections
- Arthrograms: study of joints
- Screening in theatre
What is nuclear medicine?
- Administration of radio pharmaceuticals labeled with radioactive tracers into the patient
- Use of gamma camera and PET scanner to detect radiation emitted by tracer and display as an image
- Used to display physiological function
What are the uses of nuclear medicine?
- Excretory function of jidneys, iodine-concentrating ability of the thyroid, blood flow to heart muscle can be measures
What are the limitations of nuclear medicine?
- High cost
- Radiation
What is contrast media?
- Administered by swallowing or injecting into the body to delineate anatomy and functioning of blood vessels, the genitourinary system or GI tract
- Radiocontrast agents strongly absorb or scatter X-rays, allowing demonstration of dynamic processes
- Iodine contrast can also be concentrated in abnormal areas more or less than in normal tissues, making abnormalities more obvious
What are the common uses of contrast media?
- Barium sulphate is given orally or rectally for evaluation of the GI tract
- Iodine is given by oral, rectal, vaginal, intra-arterial or intravenous routes
- Air can be used for the gastrointestinal system
- Carbon dioxide can be used in the venous system
What is interventional radiology?
- Diagnose or treat pathologies with the most minimally invasive technique possible
- Images are used for guidance as maps to allow the clinician to guide needles and catheters through the body
- By minimizing physical trauma, infection rates, recovery times and hospital stays can be reduced
What is an example of interventional radiology?
- Angiogram (x-ray using contrast media to examine coronary arteries - diagnostic purposes)
- Angioplasty (widen narrowed or obstructed arteries or veins - treatment purposes)
What is the difference between T1 and T2 weighted mode in MRI?
T2 weighted mode: water is white
T1 weighted mode: water is black
How much background radiation does a patient receive during a head CT?
1 head CT = 1 year
What are the ideal properties of a solution used as contrast media?
Low osmolality and highly soluble
