Lecture 3 & 4: An introduction to medical imaging & Radiology

Question 1

How do X-rays work?

Answer 1

• Focused bean of high energy electrons pass through body onto receiver
• Some are absorbed or scattered
• More dense = higher attenuation = lighter appearance

Question 2

What are the advantages of using X-rays?

Answer 2

• Quick
• Portable
• Cheap
• Simple

Question 3

What are the disadvantages of using X-rays?

Answer 3

• Radiation (relatively low but still present)
• One plane = 2 dimensional
• Poor soft tissue imaging

Question 4

What are some clinical examples that X-rays can be used for?

Answer 4

• Chest: infection, oedema
• Bowel: dilation, perforation
• Orthopaedic: fracture / trauma
• Post-procedure: Nasogastric rube, pacemaker
• Dentistry

Question 5

How does ultrasound scanning work?

Answer 5

• 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)

Question 6

What are the advantages of using ultrasound scanning?

Answer 6

• Studies function of moving structure in real-time
• Emits no ionizing radiation
• Relatively inexpensive
• Quick to perform
• Portable
• Can be inserted into body cavities

Question 7

What are the disadvantages of using ultrasound scanning?

Answer 7

• Very operator defendant- depends on how well the person uses it and how well they know their anatomy

Question 8

What are some clinical examples that ultrasound scanning can be used for?

Answer 8

• 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)

Question 9

How does medical resonance imaging work?

Answer 9

• 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

Question 10

What are the advantages of medical resonance imaging?

Answer 10

• No radiation
• Excellent soft-tissue contrast
• Different pulse sequences can be used for specific MRI diagnostic imaging

Question 11

What are the disadvantages of medical resonance imaging?

Answer 11

• 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

Question 12

What are some clinical examples that medical resonance scanning can be used for?

Answer 12

• 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

Question 13

How do CT scans work?

Answer 13

• X-ray tube opposite a detector in a ring-shaped apparatus rotate around a patient
• Produces computer-generated cross-sectional image

Question 14

What are the advantages of using CT scans?

Answer 14

• Quick
• Good spatial resolution (easy to distinguish between adjacent tissues)
• Can scan most areas

Question 15

What are the disadvantages of using CT scans?

Answer 15

• 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)

Question 16

What are some clinical examples that CT scanning can be used for?

Answer 16

• Diagnosis: cancer, stroke, bone injury, blood flow
• Guide further tests or treatment: radiotherapy,biopsy
• Monitor conditions: cancer treatment

Question 17

How does positron emission tomography work?

Answer 17

• Radionuclides bound to glucose (places that are metabolically active)
• PET camera detects annihilations (high energy gamma rays) from areas of high glucose metabolism

Question 18

What are the advantages of PET scans?

Answer 18

• Non-invasive diagnosis and patient management

Question 19

What are the disadvantages of PET scans?

Answer 19

• Health hazards due to radiation

Question 20

What are some clinical examples that PET scans can be used for?

Answer 20

• Images of radioactivity distribution throughout the body can show rapidly growing tissue, like tumors, metastasis or infection

Question 21

How does fluoroscopy work?

Answer 21

• 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

Question 22

What are the advantages of using fluoroscopy?

Answer 22

• Real-time imaging
• Cheap
• Interventional procedures can be conducted

Question 23

What are the disadvantages of fluoroscopy?

Answer 23

• Health hazards due to radiation

Question 24

What are some clinical examples that fluoroscopy can be used for?

Answer 24

• Angiography: examination of blood vessels
• Contrast GI studies
• Therapeutic joint injections
• Arthrograms: study of joints
• Screening in theatre

Question 25

What is nuclear medicine?

Answer 25

• 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

Question 26

What are the uses of nuclear medicine?

Answer 26

• Excretory function of jidneys, iodine-concentrating ability of the thyroid, blood flow to heart muscle can be measures

Question 27

What are the limitations of nuclear medicine?

Answer 27

• High cost

- Radiation

Question 28

What is contrast media?

Answer 28

• 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

Question 29

What are the common uses of contrast media?

Answer 29

• 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

Question 30

What is interventional radiology?

Answer 30

• 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

Question 31

What is an example of interventional radiology?

Answer 31

• Angiogram (x-ray using contrast media to examine coronary arteries - diagnostic purposes)
• Angioplasty (widen narrowed or obstructed arteries or veins - treatment purposes)

Question 32

What is the difference between T1 and T2 weighted mode in MRI?

Answer 32

T2 weighted mode: water is white

T1 weighted mode: water is black

Question 33

How much background radiation does a patient receive during a head CT?

Answer 33

1 head CT = 1 year

Question 34

What are the ideal properties of a solution used as contrast media?

Answer 34

Low osmolality and highly soluble