Radiology Concepts I & II

Radiology

study of X rays and radioactive substances and their uses in the diagnosis and treatment of diseases

Radiology Screening

Using radiology to ID risk factors, detect occult disease

Radiology diagnosis

using radiology to establish or exclude disease, early dx, or determine stage / activity of disease

Radiology Disease Management

Using radiology to estimate prognosis, monitor condition, help select therapies

Disadvantages of radiology

cost, risk of discomfort, pain, or morbidity, and incidentalomas

Incidentaloma

refers to a mass lesion involving an organ that is discovered unexpectedly by the use of ultrasound, computed tomography scan, or magnetic resonance imaging and has nothing to do with the patient's symptoms or primary diagnosis

Gold Standard Test

the test with the highest known accuracy of identifying a person as having or not having the disease being assessed

TOC

test of choice

Radiation

energy emitted from unstable atoms (radioactive energy)

Ionizing imaging

Imaging process that uses radiation

Non-ionizing imaging

Imaging process that doesn't use radiation

X-rays

Electromagnetic radiation having a very short wavelength; can penetrate substances such as skin and muscle.

Scatter radiation

A form of secondary radiation that occurs when an x-ray beam has been deflected from its path by interaction with matter

What is required by X-rays used in diagnostic radiology?

A vacuum and a high potential difference between a cathode and an anode

Radiographic Density

the degree of blackness on a radiograph

Radiographic Contrast

The difference between adjacent densities ranging between clear white through various shades of gray to black

Radiolucent

a substance that allows x-rays to pass through and appears black or dark gray on the resulting film

Radiopaque

substance does not allow x-rays to pass through and appears white or light gray on the resulting film

Radiodense

substance does not allow x-rays to pass through and appears white or light gray on the resulting film

Naturally occurring radiographic densities (calcium, adipose, air)

appear as shades of gray to black on a radiograph

Unnaturally occurring radiographic densities (metal, plastic)

appear as white

If an x-ray beam exposed the film entirely, what color would the film be?

black

What happens when a patient stands between the film and the x-ray?

Various structures in the body absorb the x-ray beams

How does the darkness and lightness occur on an x-ray film?

lightness = x-rays are absorbed by structures and do not pass through

darkness = x-rays pass through the object and meet the film

Risk of cell mutation from ionizing energy is higher for what population of people?

younger people

Why is risk of cell mutation higher for younger populations?

They have more cells dividing, more tissues growing, and longer lifespans to develop cancers

Biological effects of radiation

Deterministic (Non-Stochastic)

Stochastic (Probabilistic)

Deterministic effects of radiation

the amount of radiation imparted to a tissue that exceeds a damage threshold value

Stochastic (Probabilistic) effects of radiation

effects can manifest no matter the dose; any procedure with radiation carries some risk

ALARA

As Low As Reasonably Achievable

Ways to decrease radiation exposure

Decrease time of exposure

Increase distance from X-rays

Use shielding

Radiography

process of recording x-rays; produces a static 2D image

In reading X-Rays, what does PA and AP mean?

The way the X-ray beam travels through the body to the film

Posterior Anterior

Anterior Posterior

A provider wants to see a patient's lungs in an x-ray, how should we have the patient stand relative to the film?

Patient should stand facing the film (PA) so the lungs are closer to the film

Why do we want the object of interest in an X-ray to be closer to the film?

The further an object is from the film, the more distorted it becomes

What makes an x-ray film adequate?

Presence of intended anatomy on the image as well as proper exposure / contrasting light and dark to be able to see the structures

A patient has had a rough cough for a few weeks and the provider orders a chest X-ray to rule out infection. The provider receives an X-ray taken at an AP view. Why might the tech have taken that view?

The patient is immobile or too sick to get up. The tech can make it easier for the patient by having them lay down or sit against the film.

Fluoroscopy

visualization of body parts in motion by projecting x-ray images on a luminous fluorescent screen

Why is contrast used for imaging?

It varies the densities of certain tissues to allow them to be distinguished from each other on imaging

What are the two most common contrast agents used in imaging?

Iodine and barium

Computed Tomography (CT)

a scanning technique using multiple X-rays to construct three-dimensional images

How is a patient positioned during a CT scan?

Supine on a table

Hounsfield Unit (HU)

A numeric value in a CT scan representing the density of a certain tissue. Air = -1000 (black), water = 0 (gray), bone = 800-1000 (white)

What are window levels when viewing a CT scan?

Levels used to manipulate the grayscale to focus on certain organ systems (EX adjust levels to view lungs vs soft tissue vs bone)

Which test is faster: CT or MRI?

CT

Which test is better for detecting demyelination: CT or MRI?

MRI

Axial plane

Horizontal plane

Sagital plane

divides the body into left and right halves

Coronal plane

divides body into front and back

Magnetic Resonance Imaging (MRI)

a technique that uses magnetic fields and radio waves to produce computer-generated images that distinguish among different types of soft tissue; allows us to see structures within the brain

How does MRI work?

Uses a magnet to manipulate hydrogen atoms. Each H atom gives off a radio-frequency that is assigned a grayscale value by the computer, resulting in a highly detailed image

MRI T1

Better resolution and better for anatomy

Fat appears white and water appears dark

MRI T2

Better contrast, especially with water and better for pathology such as tumors

Fat appears dark and blood, edema, and CSF appears white

Hypointense

Areas of low intensity or decreased brightness on the MRI image

Hyperintense

Areas of high intensity or increased brightness on the MRI image

dual energy x-ray absorptiometry (DEXA)

A highly accurate method of measuring body composition and bone mass and density using multiple low-energy X rays.

DEXA T scores

compares bone mineral density to a healthy 35 year old female's.

DEXA Z scores

compares bone mineral density to age/sex-matched control

DEXA T & Z scales

Less than -2.5 = osteoporosis

-2.5 to -1 = osteopenia

Greater than -1 is normal

Nuclear Medicine

Uses radioactive materials either to image a patient's body or to destroy diseased cells

Radiopharmaceuticals

radioactive substance used for diagnostic or treatment purposes

Scintigraphy

diagnostic nuclear medicine test using radiopharmaceuticals and gamma cameras to create images

single photon emission computed tomography (SPECT)

radioactive tracer is injected intravenously and a computer reconstructs a 3D image based on a composite of many views

Positron emission tomography (PET)

a method of imaging that assesses metabolic activity by using a radioactive substance injected into the bloodstream

Ultrasound

Images created via the sending and returning of soundwaves from and to a transducer

Echogenicity

The property of a tissue that allows it to reflect ultrasound waves

hyperechoic

Increased reflection of ultrasound waves

isoechoic

having the same echogenicity

hypoechoic

Low-level echoes within a structure

sonolucent

without echoes, same as anechoic

attenuation

Loss of power in a signal as it travels from the sending device to the receiving device

Doppler shift

the shift to a different wavelength caused by sound passing something moving

Acoustic shadow

the area on the side of the head opposite from the source of a sound in which the loudness of a sound is less because of blocked sound waves