(1) fundamental principles of imaging modalities

who is wilhelm conrad roentgen?

discovered the first x-ray image in 1896

what was the first x-ray picture of?

his wife anna bertha’s hand

how does radiography work?

• x-ray source on one side of patient & x-ray detector on the other side

• short duration (<1.2 second) pulse of x-rays is emitted by the tube

  • most rays interact with the patient

  • some pass throught the patient and reach the detector

what causes a heterogeneous pattern of x-rays reaching detector?

different attenuation patterns of tissue

how does fluoroscopy work?

continuous/pulsed x-ray beam passed through body to create real-time, moving images on a monitor

what is endoscopy?

non surgical procedure where doctor uses a thin flexible tube equipped with light and camera (endoscope) to examine the inside of the body

• digestive tract usually

what is mammography?

specialized low dose x-ray image of breast

• special detector used to accentuate contrast in breast

what do you need to see in breast mammography?

• glandular and fatty tissues

• skin line of breast

when did computed tomography become clinically available?

1970s

what is computed tomography?

passes x-rays through body at large number of angles

• done by rotating x-ray tube around patient

how are these images produced in CT?

computer synthesizes the data into tomographic images

• tomographic images eliminate superposition of anatomical structures

• you get unobstructed view of the anatomy

the radiation burden in the US has increased due to

CT

• ½ of all medical radiation is due to CT

what is an angiogram?

type of vascular interventional radiography

• dye that is visible by an x-ray machine is injected into blood vessels of the heart

• x-ray rapidly takes a series of images (angiogram)

how do stents appear on xray?

bright, metallic, tubular/cylindrical mesh structures

what is cardiac balloon angioplasty and stenting?

when a balloon tipped catherter is inserted in artery

• balloon is inflated to flatten plaque & expand artery

• mesh tube/stent is placed to keep artery open

what is MRI?

radiation free medical imaging technique that uses powerful magenetic fields (10,000-60,000) times stronger than earth’s magnetic field

how does MRI work?

it uses the magnetic resonance properties of protons

• nucleus of hydrogen atom (which are abundant in biological tissues)

produces 3D detailed images

what is nuclear medicine?

FUNCTIONAL imaging

• shows how organs and tissues work (physiology)

• not for structural images

how does nuclear medicine work?

uses tiny amounts of radioactive materials that are injected, inhaled or swallowed → therefore the patient is the source of radiation

• produces EMISSION images as opposed to transmission images

  • this is because the radioisotopes emit their energy from inside the patient

what are the types of nuclear medicine imaging?

PET, SPECT, PET/CT

what is SPECT?

single photon emission computed tomography

• 3D nuclear imaging test

• computer is used to create cross sectional pictures of parts of the body

• good for stress test imaging

what is PET?

positron emission tomography

• nuclear imaging that allows visualization of physiologic proceses in body

• imaging, characterization, quantification of bio processes, stages → all happen at cellular and subcellular levels of living subjects

what is the difference between SPECT and PET scans?

PET

• higher resolution

• better sensitivity

• faster scan times
  

SPECT

• more widely available

• less expensive

• uses tracers with longer half lives

what is the speed of sound in tissue?

1540 cm/s

what is radiation? types?

energy that travels thorugh space or matter

• electromagnetic (EM)

• particulate

what is ionization vs non ionization?

non ionizing

• any type of EM radiation that does not carry enough energy to change atoms/molecules

ionizing

• high energy EM waves

• removes electrons from atoms → can break chemical bonds in molecules/ change basic make up of atoms in cells

what is a sound wave?

MECHANICAL wave of pressure

*requires a medium to propagate

what are EM waves?

• form of energy emitted and absorbed by charged particles transmitted as oscillating electric and magnetic fields

• can travel through vaccum

which cells are more sensitive to radiation effects?

• actively dividing cells

  • bone marrow

  • lymph glands

  • gonads

who is the most susceptible to radiation effects?

children and developing fetuses

what is the ALARA principle?

as low as reasonably achievable

• minimize time of exposure

• double distance between body and radiation source (reduced radiation exposure by factor of 4)

• shielding : use absorber materials such as plexiglas for beta particles and lead for x-rays/gamma rays

what is the best distance from radiation source?

6ft

when is organogenesis?

betwen 8-15 weeks of pregnancy

• this is when fetus is more sensitive to radiation induced effects

most medical sources of radiation exposure come from

computed tomography (24%)

most background radiation exposure comes from

radon and thoron (37%)

what are mild anaphylactoid reactions to contrast media?

mild urticaria (hives)

mild pruritis (itchy skin)

what are intermediate anaphylactoid reactions to contrast media?

more severe urticaria (hives)

hypotension

mild bronchospasm

what are severe anaphylactoid reactions to contrast media?

severe bronchospasm

alryngeal edema

unconsciousness

convulsions

pulm collapse

cardiac arrest

what increases risk of anaphylactoid reactions to contrast media?

history of asthma (10x)

history of atopy (10x)

• genetic tendency to develop allergic diseases

previous anaphylactoid reaction to iodinated contrast media

what is contrast induced nephropathy (CIN)

refers to greater than 25% reduction of renal function occuring within 3 days of contrast medium injection

• most cases resolve in 1-2 weeks

what are risk factors for CIN?

pre-existing impaired renal function

dehydration

sepsis

age >60 years

what are safety issues for MRI?

metallic items

medical equipment

implanted items in patients

nephrogenic systemic sclerosis