advantages and disadvantages of common imaging modalities Flashcards
Different Imaging Modalities
(1) X-ray
(2) Computed Tomography (CT)
(3) Magnetic Resonance (MR)
(4) Ultrasound (U/S)
(5) Nuclear Medicine
What modality
Uses a single pulse of ionizing radiation
-Radiation dose is low but some views have more radiation than others.
X-ray
X-ray
Good for
Bad for:
Good for: bones and airspaces
Bad for: soft tissue and overlapping structures
X-ray film is _____ to start with
Turns ______ when hit with ionizing radiation (x-ray)
- White
2. Dark
Five basic radiographic densities Air \_\_\_\_\_\_ Fat \_\_\_\_\_\_ Fluid/blood/soft tissue \_\_\_\_\_\_ Bone \_\_\_\_\_\_ Metal/contrast \_\_\_\_\_
(a) Air (Darkest)
(b) Fat (Less Dark)
(c) Fluid/Blood/Soft Tissue (Gray)
(d) Bone (White)
(e) Metal/Contrast (Most White)
______ are two- dimensional representation of a three-dimensional object.
-Therefore, structures can overlap and hide underlying structures depending on the
viewpoint.
- It is important to obtain more than one view
X-rays
What Xray view?
Used if patient is unable to stand or sit for a PA view
Lower quality than PA view
Back is placed next to the film
Heart is magnified and borders are fuzzier
Anteroposterior (AP “front to back”)
What Xray view?
Usually taken in conjunction with a PA view
Allows viewing of structures behind the heart (mediastinum) and provides three dimensional
image.
Lateral (LAT “side view”)
What xray image?
at an angle used mostly on limbs
Oblique (OBL)
What xray image?
used in Chest X-ray “mostly”
1) Object that is closer to the film has sharper borders
2) Chest is placed next to the film thereby placing most of the important structures,
such as heart and great vessels, closer to the film.
3) Heart size is minimally magnified and borders are sharp
Posteroanterior (PA “back to front”)
What modality?
Similar to x-ray:
(a) Emits radiation
(b) Shows color in black, white, and gray depending on density
(2) Uses multiple pulses (“shots”) of ionizing radiation
(a) Radiation dose is high
Computed Tomography (CT)
Computed Tomography (CT)
Good for: _________
Bad for: ________
Good for: Bone, airspaces, some soft tissue and overlapping structures (especially abdomen and in trauma).
Bad for: Some soft tissues (nerves, muscles, connective tissue), patients with retained metallic objects (causes artifacts).
Views for what modalities
(a) Sagittal or Median
(b) Coronal
(c) Axial or Transverse or Cross-sectional
Ct, mri
What modality
Uses electromagnetism and radio frequency properties.
(a) No exposure to ionizing radiation, but time consuming
Magnetic resonance (MR)
Magnetic resonance (MR)
Good for: ______________
Bad for: __________________
Good for: Soft tissue (nerves, muscles, connective tissue, brain, joints).
Bad for: People who cannot hold still or have ferrous metal in the body.
What modality? Uses sound waves (similar to SONAR) (a) No radiation, but can’t go very deep (b) Operator dependent (c) Image produced is a focused segment of the object (d) Rapid and portable
Ultrasound (U/S)
Ultrasound (U/S)
Good For: ____________
Bad for: _______________
Good for: Determining fluid vs solids, abdominopelvic imaging (gallbladder, kidneys,
uterus, testis), assessing blood flow (Doppler).
Bad for: Things under bones (chest) and air filled chambers, deep things
views of what modality
Longitudinal (same as sagittal)
Transverse (same as axial)
U/S
What Modality
(1) Radioactive agent is given intravenously
(2) The agent participates in physiologic processes while emitting radiation
(3) The radiation is detected and is used to create an image showing the distribution of the
agent within the body.
(4) A typical use is to detect stress fractures before being visible on x-ray
Nuclear Medicine
What modality?
Good for: Detecting normal or abnormal physiologic processes
Bad for: Showing less anatomic detail
Nuclear Medicine
