MS-1 FUND 1: 9:10-10:00
Thursday, September 18, 2014
Dr. Sonavane
Imaging
Transcriber: Katherine Shelton
Editor: Jordan Busing
Page 1 of 2
Abbreviations: CT – computed tomography, MRI – magnetic resonance imaging, mSv - millisievert
Introductory Comments: This is the second hour of Dr. Sonavane’s lecture on imaging. Before this lecture Dr. Cotlin
made an announcement confirming that everyone has TBL Monday morning at 8:10, and that the information we are
responsible for learning is in the vodcast on MedMap. (S.N. Dr. Sonavane’s presentation did not always go in order the slides are in the
powerpoint on MedMap. This transcript is written in the order the points were given, but the slide numbers correspond to the slides on MedMap.)
I.
Radiation (slide 37) 9:10
a. When X-rays were first used, problems caused by radiation were not as well known and many modern
precautions were not taken.
b. Ionizing imaging can have many hazards so you will see caution signs where they are performed (especially
gamma rays, which are more ionizing than X-rays) (slide 53)
c. Radiation hazards can take two forms (slide 58) 10:20
i. Sudden exposure to a lot of radiation (such as in nuclear accidents, atomic bombings)
1. Causes radiation sickness and acute damage, especially to rapidly dividing cells
a. Can cause burns to skin, bleeding in epithelium of GI tract
2. Examples:
a. Victim of nuclear explosion showing burns (slide 54) 11:27
b. Two men discovered a Stalin canister of radioactive material in Soviet Georgia and used it for
warmth; developed radiation sickness (slide 55)
c. Woman who received radiation treatment for lymphoma suffered burns and radiation induced
skin damage (slide 56)
ii. Continuous exposure to small amounts causing accumulation
1. Happens more often due to medical imaging
d. Radiation risks (slide 57) 12:54
i. 600,000 annual CTs lead to 500 deaths attributable to cancer in pediatric population
1. Children are more sensitive to radiation and take longer to have cancerous changes, so risk still
exists 1-2 decades after exposure
2. Radiation is especially harmful to children and fetuses because it affects rapidly dividing cells
a. Hematopoietic cells are also affected because of rapid division
ii. 1% of cancer in the US is due to medical exposure
iii. Annual collective dose from medical exposure in US is equal to worldwide collective dose from Chernobyl
e. Comparative Effective Doses (slide 59) 14:13
i. Different procedures involve different doses of radiation, with a chest radiograph being lowest (0.02 mSv)
and an abdomen (three phase liver) CT being highest (30 mSv)
1. A three phase liver CT has 3x the dose of abdomen and pelvis CT because it passes three times
ii. Yearly background radiation (3.6 mSv) – a person’s exposure to radiation just from being on Earth with
no medical exposure
iii. Radiation Dose Comparison Table compares the dose of radiation from different procedures by showing
the number of chest X rays needed to reach an equivalent dose (slide 60) 16:03
1. For chest x-ray equivalents: Barium enema = 400; CT head = 100; CT abdomen = 400
f. Risk of death by cancer from 10 mSv (one CT) one-time exposure is 1:2000 (slide 61) 16:30
i. Comparable 1:2000 risk for death include (slide 62) 16:45
1. Smoking 140 cigarettes in a lifetime (risk for lung cancer)
2. Spending 7 months in New York City (risk for lung cancer)
3. Driving 4,000 miles in a car (risk of death by accident)
4. Flying 250,000 miles in a plane (risk of death by accident)
g. In the X ray department, everyone is constantly exposed to radiation (slide 63) 17:01
i. When radiation accumulates over time, it affects hemopoietic cells and causes malignancies such as
lymphoma and leukemia
ii. Picture from UAB’s fluoroscopy unit shows protective measures: (slide 64) 17:25
1. Gowns with 0.5 mm lead shield to protect from scattered radiation
a. Rays scatter from the patient’s body, so workers have some exposure
2. Radiation safety badge that can detect how much radiation a person has been exposed to over time
II. Magnetic Resonance Imaging (MRI) (slide 66) 19:40
a. MRI is a non-ionizing imaging technique – does not expose the patient to radiation
b. Basic principle: (slide 65) 20:50
i. The body is full of water, which means there is an abundance of H+ ions
ii. The MRI tube houses a giant magnet, which causes H+ ions to align in the direction of the magnetic field
iii. Different radiofrequency pulses are applied to disturb the MRI field, and the deviation/return of proton
alignment to the magnetic field is measured
MS-1 FUND 1: 9:10-10:00
Thursday, September 18, 2014
Dr. Sonavane
Imaging
Transcriber: Katherine Shelton
Editor: Jordan Busing
Page 2 of 2
Abbreviations: CT – computed tomography, MRI – magnetic resonance imaging, mSv - millisievert
iv. MRI is used to get different signals from different structures in the body
c. MRI is useful for soft tissues that contain a lot of water (e.g. muscle, tendon) (slide 67) 22:10
d. In an MRI of the brain, white and gray matter is easily differentiated (slide 68) 22:30
i. In this image, the white regions are the ventricles
ii. Can see a tumor in the basal ganglia (rounded, grey mass in right side of brain)
e. Shortcomings of MRI 23:20
i. It is a lengthy procedure – an abdominal CT will take ~3 seconds whereas an MRI will take 40-45 min
ii. If proper precautions are not taken, metal can get pulled in (shown on slide 69 and 70) 23:55
f. Modifications of MRI (slide 71) 24:45
i. Patients, especially children, can get claustrophobic and must stay still for a long time
1. Motion can cause artifacts on the image
2. Children are often put to sleep for MRI, but there are complications with this
3. Open MRIs can be used for small areas
a. Also used on adults (slide 72) 25:44
g. MRI machines are very heavy – example of how an MRI machine was delivered to UAB (slides 73-76) 25:54
III. Ultrasound (slide 77) 26:38
a. Has monitor and probe used on the patient
b. Principle of Ultrasound (slide 78) 27:04
i. Same principle as detecting enemies in submarine via sonar detection system
ii. Sound waves are sent out, then hit a target and echo back
c. Ultrasound image of a gallbladder (slide 79) 27:50
i. Not as fine an image as a CT or MRI
ii. Advantages:
1. Non-ionizing, so no danger of radiation exposure
2. Very quick, easy, and portable – can be used at the bedside or in ER
3. Good for looking at solid/fluid filled organs (e.g. gallbladder, liver, spleen, pregnant woman’s uterus)
a. Fluid looks black on ultrasound
d. Ultrasound image of fetal skull – black is amniotic fluid surrounding fetus (slide 81)
e. Can use ultrasound data to construct a 3D image (slide 82) 30:40
f. Ultrasound is not useful for air-containing organs or bony/calcified structures
i. Air and bone do not allow sound waves to go past
ii. Fetal bones are visible because they are not yet fully calcified
iii. Ultrasound use is also limited for large patients because the waves cannot penetrate deep enough
IV. Charges and Fee Schedule (slide 83) 32:58
a. Professional and technical fees (SN: see slide for examples of rates)
i. The first number is how much the insurance is asked to pay, and the second is how much is actually paid
b. If you own your own imaging machine, you can charge a global fee – the sum of professional and technical fees
V. ALARA – “As Low As Reasonably Achievable” (slide 84) 34:15
a. There is a balance: need to get information, but need to keep radiation exposure at a minimum
b. In the late 90s, a hair loss pattern was seen in patients who had CT perfusion study done (slide 86) 34:46
i. Used on patients who experience acute stroke – sudden occlusion of brain blood vessel
ii. Hair follicles damaged because of improper technique – too many radiation slices performed at same level
c. Ways to control exposure (slide 85) 36:57
i. External exposure control
1. Time – reducing the time the scan takes reduces exposure
2. Distance – inverse square law – when distance from radiation is increased, exposure decreases by
the square of the distance
a. Ex: if you move two feet away from the X ray, your radiation exposure decreases by 4x
b. SN:(Info from other sources) This is the inverse-square law in physics that states that intensity is inversely
proportional to the square of the distance from the source of the radiation, i.e. 𝑖𝑛𝑡𝑒𝑛𝑠𝑖𝑡𝑦 ∝
1
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 2
3. Shield – must use appropriate shielding at all time
ii. Internal exposure control – applies more to gamma rays than X rays
1. Protective gear – workers are preparing the radiopharmaceuticals themselves
2. Good hygiene – must be careful about spills while transporting and injecting radiopharmaceuticals
3. Swipe survey –quality control procedure in nuclear medicine to make sure there is no contamination
4. Methods to control contamination if it occurs
VI. ARS question: 41:24
<END OF LECTURE 42:00>