Physics Quiz #8(Radiation, MRI and Pulse Oximetry) Flashcards
The analysis of Electromagnetic Radiation interaction with matter is the underlying principle of what four things used in healthcare?
- X-Ray fluoroscopy
- Anesthetic Gas Analysis
- Pulse Oximetry
- Lasers
The operation os what monitoring device uses Beer’s law?
Pulse oximetery
Explain how a pulse oximeter works.
- 2 different wavelengths of light are used: one is visible red(wavelength = 660 nanometers) and the other is infrared(wavelength = 990 nanometers).
- Infrared light(990 nm) is absorbed by oxyhemoglobin, and red light(660 nm) is absorbed by deoxyhemoglobin.
- The differences in absorption are used to calculate the oxygenation saturation.
What two principles are combined in the pulse oximeter to measure oxygen saturation in arterial blood?
Pulse oximeters combine the principles of oximetry and plethysmography to measure noninvasive oxygen saturation in arterial blood.
What does a finger plethysmography detect?
A finger plethysmography uses a light-emitting diode and a photoelectric cell to detect changes in finger volume.
The Lambert-Beer law is based on what observation and applies to what monitoring modality?
- The Lambert-Beer law is based on the observation that oxygenated hemoglobin and reduced hemoglobin differ in their absorption of red and infrared light.
- This law forms the basis of pulse oximetery.
Identify the two light sources in the photo diode of the pulse oximeter.
Red light(60 nanometers wavelength) and infrared light(990 nanometers wavelength).
List the absolute and relative contraindications to pulse oximetry.
There are no contraindications to pulse oximetery!
List four examples flow perfusion states that can cause pulse oximetery artifact.
- Low cardiac output
- Anemia
- Hypothermia
- Increases systemic vascular resistance
What 10 factors, unrelated to low perfusion, interfere with an accurate pulse oximeter reading?
- carboxyhemoglobin gives a false high reading
- methemoglobinemia gives false low reading
- excessive room ambient light, or overhead infrared lights
- tremors or vibrations of the patient
- methylene blue dye
- venous pulsations
- deeply pigmented skin
- fingernail polish
- light leakage from the light sources to the light detectors
- low oxygen saturations(< 70%)
Can the pulse oximeter detect a ventilation:perfusion mismatch? Why or why not?
- Yes
- PaO2 decreases when a ventilation:perfusion mismatch develops
- Since SaO2 decreases when PaO2 decreases below 100 mmHg, a pulse oximeter can detect a ventilation:perfusion mismatch
What are the two best monitors to detect ventilator disconnection?
- capnography and spirometery
- the next best monitors for detecting ventilator disconnect are pulse oximetry and stethoscope
What two measurements assess blood oxygen?
PaO2
SO2
What are the 4 types of radiation?
- alpha radiation
- beta radiation
- gamma radiation
- x radiation
What are the physical properties of alpha radiation?
It is a heavy, very short-range particle and is actually an ejected helium nucleus.
What are two characteristics of alpha radiation?
- most alpha radiation is NOT ABLE TO PENETRATE HUMAN SKIN or clothing
- Alpha-emitting materials can be harmful to humans if the materials are inhaled, swallowed or absorbed through open wounds
What are the physical properties of beta radiation?
Beta radiation is a light, short-range particle and is actually an ejected electron.
What are 2 characteristics of beta radiation?
- Beta radiation may travel several feet in air and is moderately penetrating. Clothing provides some protection against beta radiation.
- Beta radiation can PENETRATE HUMAN SKIN TO THE “GERMINAL LAYER”, WHERE NEW SKIN CELLS ARE PRODUCED. If high levels o beta-emitting contaminants are allowed to remain on the skin for a prolonged period of time, they MAY CAUSE SKIN INJURY.
What is Gamma radiation?
Gamma radiation and X-rays are highly penetrating electromagnetic radiation.
What are 2 characteristics of gamma radiation?
- Gamma radiation or X-rays are able to travel many feet in air and many inches in human tissue
- They readily penetrate most most materials and are sometimes called “penetrating” radiation.
What type of radiation are X-rays and example of?
Gamma rays
What are two examples of “penetrating” radiation?
Gamma rays and X rays
What type of materials are needed to shield for gamma radiation?
Dense
What are the 3 categories of radiative materials we are constantly being exposed to?
- primordial radionuclides
- cosmogenic radionuclides
- anthropogenic radionuclides
What is primordial radionuclides?
Primordials radionuclides and their progeny have been around since the solar system and earth existed and make EXCELLENT TIME-MEASUREMENT TOOLS because their known half-lives and decay properties(“radiometric dating”).
What is cosmogenic radionuclides?
Cosmogenic radionuclides are formed when radiation from space, called cosmic rays, interact with matter. Cosmogenic radionuclides are formed continuously and include things such as 3H(tritium) and 14C. 14C has a 5730 half-life- By measuring the 14C/12C RATIO, the age of an artifact from an organism that was previously living can be readily established.
What is anthropogenic radionuclides?
Anthropogenic radionuclides occur n the environment as a RESULT OF HUMAN ACTIVITIES including nuclear medicine, electricity generation by nuclear power stations and nuclear weapons testing.
What is the unit which expresses the risk of the occurrence of the stochastic effects associated with all possible exposure situations? The indicator is known as the “effective dose”.
Sievert(Sv)
How is the effective dose calculated as related to Sievert?
from the dose absorbed by the various exposed tissues and organs, by APPLYING WEIGHTING FACTORS which take into account the RADIATION TYPES(alpha, beta, gamma, X-rays, neutrons), THE MEANS OF EXPOSURE(external or internal) and the SPECIFIC SENSITIVITY OF THE ORGANS OR TISSUES.
What amounts of radiation do X-rays and mammography usually produce?
low amounts of radiation
What amounts of radiation do Cat scan, fluoroscopy and nuclear medicine procedures produce?
higher amounts of radiation
What 4 organs are especially sensitive to low radiation exposure?
- reproductive cells/gonads
- red bone marrow
- breast tissue
- thyroid gland
On a C-arm where is the radiation coming from?
The X-ray source of C-arm fluoroscopy machine is coming the the “little disk”
On a C-arm where does the radiation go too?
towards the image detector(the large glass plate)
Where on the patient should the shield be placed in relation to where the radiation enters the body?
The shield should be placed on the patient bodies between the radiation source(i.e. the “little disk”) and the body.
What is the purpose of the lead shield?
The lead shield is used as a barrier between the X-ray beam and the patient’s body.
If the C-arm is placed where the X-ray source is coming from above the patients body part, where would the shield be placed?
the shield would be placed on top of the patient
If the C-arm is placed where the X-ray source is coming from under the patients body part, where wold the shield be placed?
the shield would be placed under the patient
What is Magnetic Resonance Imaging?
MRI is a diagnostic procedure that uses a combination of a LARGE MAGNET, RADIO FREQUENCIES, and a computer to produce detailed images of organs and structures within the body. It is an important tool to help improve the accuracy of diagnoses and treatments of broad categories of diseases including stroke, brain tumors, epilepsy, musculoskeletal and heart disease.
What do MRIs use to create cross-sectional images of anatomy?
MRIs use a magnetic field and radio waves to create cross-sectional images of anatomy.
What is the key to image clarity with MRIs?
The magnet strength is the key to image clarity: the stronger the magnet, the more clear the image.
What are the two types of MRI scanners as related to magnet strength and in what instances would they be used?
1.5 T and a 3T; 3T is stronger with more detail. If someone has braces for instance they would go to the smaller one.Magnets that pick up junk cars have a strength of about 1.5T. Or, put another way, the 3T is 60,000 times as powerful as the earth’s magnetic field.
Why is MRI used in some situations instead of CT scan?
MRI may be used instead of a CT scan in situations where organs or soft tissue are being studied, because bones do not obscure the images of organs and soft tissues, as they do in CT.
Is there any risk of radiation exposure with MRIs?
no
How do MRIs work?
The magnetic field alters the hydrogen atoms’ natural alignment in the body. The radio waves knock the nuclei of the atoms in your body out of their normal position. As the nuclei realign back into proper position, they send out radio signals. These signals are received by a computer that analyzes and converts them into an image of the part of the body being examined. This image appears on a viewing monitor.
What are the 3 planes in which thin “slices” are produced by an MRI?
sagittal
coronal
axial
What is the sagittal plane?
divides the body RIGHT and LEFT
What is the coronal(frontal) plane?
divides the body FRONT and BACK
What is the axial plane?
divides the body into TOP and BOTTOM
When is MRI contraindicated for the patient and you as the anesthesia provider?
Due to the use of the strong magnet, MRI cannot be performed on patients with :
implanted pacemakers, intracranial aneurysm clips, cochlear implants, certain prosthetic devices, implanted drug infusion pumps, neurostimulators, bone-growth stimulators, certain intrauterine contraceptive devices, or any other type of iron-based metal implant. MRI is also contraindicated in the presence of internal metallic objects such as bullets or surgical clips, pins, ect.
What are some objects containing metal that are prohibited in the MRI suite?
- all jewelry(except wedding bands)
- hair clips, bobby pins, hair bands
- scissors, cell phones, pens, pagers
- Identification badges and credit cards with magnetic strips
What are some things the patient should inform the radiology technician before an MRI.
- chance of being pregnant
- implanted medical devices
- retained hardware(metal screws/pins/bars,ect.)
- spaces, palate expanders-not compatible
Considerations when anesthetizing a patient in the MRI scanner.
- cables should be parallel to the main magnetic field
- keep cables straight, avoid loops
- coils, cables or iv tubing should not touch the patient’s skin-pad/insulate between patient and equipment
- avoid skin to skin contact-place padding
- MRI is loud! use ear plugs or head phones
- the transfer of energy to living tissue has a warming effect and this heat can cause potentially 2nd and 3rd degree burns
- keep the patient in a neutral position
MRI-capatible is _____ equipment.
non-ferrous
In case of an emergency situation such as a code, can the resuscitation occur in the MRI suite?
No, the patient must immediately be removed from the MRI suite.
What are the two basic types of waves?
transverse and longitudinal
What are transverse waves?
composed of up-and-down movement-the medium particles move perpendicular to wave direction. Like the heavy rope at the gym…moving it up and down
What are three examples of transverse waves?
vibration of a string
electromagnetic radiation waves
heavy rope at the gym
What is the meaning of amplitude in relation to waves?
how high the waves go
What is the meaning of wave length in relation to waves?
the distance between the high points and low points in the waves. Peaks and troughs.
What are longitudinal waves?
a wave moving if the vibration of the particles of the medium are in the direction of wave propagation. It is the wave movement back and forth like a slinky, not up and down but in and out…back and forth.
What are some examples of longitudinal waves?
sound waves, ultrasound, tsunami waves, earthquake, P-waves, water waves and waves in a “slinky”
What is another name for longitudinal waves?
they are also known as compression waves, they proceed in the form of compression and rarefaction(decompression).
What happens to the velocity of the pressure wave as it is transmitted from large arteries to small arteries in the periphery?
- the velocity of the pressure wave increases
- the pressure wave in the periphery travels 15 times faster than in the aorta.
In the aortic arch the pulse wave travels ____ m/sec.
3 - 5 m/sec
The pulse wave of the subclavian artery travels _____ m/sec.
7 - 10 m/sec
In the small non-distensible peripheral arteries the pulse wave travels _____ m/sec.
15 - 30 m/sec
Longer peripheral arteries with small diameters will cause the blood to flow _____ due to increased velocity.
faster
The contour of the pulse wave depends on what 3 factors as it changes as it moves more peripherally.
- velocity of the pressure wave
- duration of the pulse
- length of the vessel
Does peripheral pulse waveforms have less amplitude or greater amplitude?
greater
What happens when a pulsatile pressure wave enters the peripheral arteries and distends them?
The pressure in these peripheral arteries causes the pulse wave to begin traveling backwards.
