Cytopathology
Ultrasound guided fine needle aspiration (USFNA)
Ultrasound terminology
Copyright: 2002-2024, PathologyOutlines.com, Inc.
PubMed Search: Terminology [title] ultrasound
Ultrasound guided fine needle aspiration (USFNA)
Ultrasound terminology
Last author update: 1 March 2013
Last staff update: 26 May 2021
Copyright: 2002-2024, PathologyOutlines.com, Inc.
PubMed Search: Terminology [title] ultrasound
Table of Contents
General imaging terminology | Basic ultrasound machine function terminology | Key ultrasound terms used to describe the sonographic image and US wave interactions with tissuesCite this page: Jakowski J. D., Meanor S. Ultrasound terminology. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/cytopathologyfnaterminology.html. Accessed April 23rd, 2024.
General imaging terminology
- DICOM (Digital Imaging and COmmunication in Medicine) standard: an imaging standard with a specific file format and a network communications protocol that allows collected images including epidemiological information to be interconnected and transferred to other systems for viewing, printing, and electronic storage
- PACS (Picture Archiving and Communication System): a medical imaging technology which provides electronic storage, retrieval, and access to images in which the universal format of the input data is in DICOM standard
Basic ultrasound machine function terminology
- Calipers: a cursor that is electronically superimposed over the cross sectional image that is used to calculate size of the scanned structure; measurement is typically given in centimeters
- Depth control: increases or decreases the depth of the field of view and is typically a running scale at one margin of the sonogram with the depth measurement in centimeters; as the depth is increased with a linear array transducer, the width of the field of view will remain constant but the image on the screen will become narrower and the structures smaller
- Doppler ultrasound: allows assessment of tissue vascularity
- Several different types of Doppler US exist but the pathologist will find that color flow Doppler or power Doppler will suit their most basic needs:
- Color flow doppler: based on the Doppler principle to detect moving objects (red blood cells within vascular spaces) and assigns a color to the movement relative to the transducer
- Gives the direction and velocity of blood flow
- Blood flow moving away from the transducer will be blue and blood flow towards the transducer will be red (note: the corresponding colors, however, can be set by the operator on the US machine)
- Absence of blood flow is indicated by the absence of color
- Angle of transducer with respect to the blood flow will affect detection of flow (at a 90 degree perpendicular scanning angle, flow may appears absent!)
- Important to keep the on screen color Doppler box as small as possible when evaluating the area of interest to maximize sensitivity
- In general, the pathologist will not be interested in the direction or velocity of flow in a tissue or target, but in the presence or absence of flow, the distribution of flow within a target (peripheral versus central), and the overall quantity of flow (minimal, moderate, or high flow)
- Power doppler: useful adjuvant to color flow Doppler; essentially measures the "magnitude" of blood flow (essentially related to the number of RBC creating the Doppler shift) without regard to direction or velocity of blood flow
- Considered more sensitive than color flow Doppler for detection of low blood flow
- Less angle dependence than color flow Doppler in detecting blood flow
- Disadvantage is that it is more susceptible to tissue and patient movement artifact (so called flash artifact) due to higher sensitivity
- Focal zone: a point where the US beam emitted from the transducer is at its narrowest and gives you the best lateral resolution
- Can be adjusted manually to a selected depth on most US machines and is usually indicated by a single marker at the edge of the depth measurement
- When manually adjusting, the focal zone should be placed at or slightly below the target
- An inappropriately positioned focal zone may cause subtle masses to be less visible, sharp edges of a target to appear ill defined, and cysts to appear as solid tissue
- Some US machines have the capability of applying more than one focal zone on an image, however, this may slow down real time scanning and may decrease image resolution
- Frequency adjustment: a keyboard control used to either increase or decrease the US frequency of the transducer within a narrow range of a few Megahertz
- High US frequencies have less tissue penetration
- Lower frequencies have more tissue penetration
- As a rule of thumb, deeper targets are imaged using lower US frequencies and superficial targets, higher frequencies
- There is an inverse relationship between sonographic resolution and scanning US frequency
- Higher frequencies have a better sonographic resolution
- Lower frequencies have a poorer sonographic resolution
- During US scanning, you will need to select a scanning frequency that optimizes both tissue penetration and sonographic resolution
- Linear array US transducer: a high frequency transducer with a linear set of piezoelectric crystals that gives good resolution in superficial tissues but does sacrifice tissue penetration as these two properties are inversely proportional; the sonogram produced is rectangular and the extent of visualization is usually limited to the footprint area
- On screen indicator: a colored mark or symbol in the upper left hand corner of the US display screen used for orientation purposes with the transducer indicator
- On screen orientation: by convention this is the proper orientation during US scanning in which the transducer indicator corresponds to the on screen indicator
- Overall gain: allows you to increase or decrease the brightness of the entire sonogram similar to the "brightness" control on a computer monitor
- Piezoelectric crystals: found under the footprint area of the transducer, has two functions:
- Vibrates when a voltage pulse is applied and creates the mechanical US waves (1% of the time during US scanning)
- Receives the pressure changes from the reflected US waves from the tissue (99% of the time during US scanning) that induce a mechanical vibration in the "listening" crystals which is converted into an electrical signal and processed by the US machine into the sonographic image
- Sonogram: 2 dimensional, grey scale, digital image representing both the strength and depth of the reflected US waves back to the transducer
- Time gain compensation (TGC): allows stepwise control of the brightness of the reflected US waves from different depths of the tissue to produce a desired uniform brightness of the sonogram
- Transducer footprint: portion of the transducer area that makes contact with the patient's skin and area in which the piezoelectric crystals are found
- Transducer frequency: usually a narrow range of a few Megahertz (e.g. 8 - 12 MHz) of scanning US frequencies that may be increased or decreased with a keyboard control on the US machine
- Transducer indicator: a colored mark or palpable protuberance at one end of the long axis of the transducer casing used for orientation purposes with the display screen
- Transducer scanning positions:
- Transverse: axial (right to left) orientation of the ultrasound probe with the transducer indicator notch towards the patient's right such that the left side of the sonogram should display structures on the patient's right side
- Longitudinal (also called Sagittal): cranial to caudal orientation of the ultrasound probe with the transducer indicator notch towards the patient's head such that the left side of the sonogram should display structures nearer to the patient's head
- Radial: used in breast US and follows a wagon wheel pattern of scanning with the nipple in the center to visualize the breast plane parallel to the ductal system
- Antiradial: used in breast US and is a scanning plane 90 degrees to the radial scanning pattern and is used to visualize the breast plane perpendicular to the ductal system
- Ultrasound transducer: produces the mechanical US waves and also receives the returning US echoes reflected from the patient's tissue boundaries and interfaces
Key ultrasound terms used to describe the sonographic image and US wave interactions with tissues
- Acoustic impedance: the resistance of tissue boundaries and interfaces to the passage of the US waves
- Anechoic: without returning echoes; appears completely black on US
- Echogenicity: the ability of a structure or tissue to return reflected US waves
- Edge shadow artifact: narrow hypoechoic lines that run parallel to the US beam and appear at the lateral edges of tissue, cysts, or masses that are smooth and rounded
- Heterogeneous: nonuniform in echogenicity and is a mixture of hyperechoic and hypoechoic areas
- Homogenous: uniform or equally distributed echogenicity
- Hyperechoic: highly reflective tissue with stronger returning echoes then the surrounding tissues; appears as a lighter shade of grey or white on US
- Hypoechoic: less reflective tissue with lower returning echoes then the surrounding tissues; appears a darker shade of grey on US
- Isoechoic: has the same shade of grey as the surrounding tissue of reference
- Posterior acoustic enhancement: a hyperechoic area in the sonogram at the posterior interface of the tissue or structures
- Posterior acoustic shadowing: a hypoechoic or anechoic area in the sonogram at the posterior interface of the tissue or structures
- Reverberation artifact: multiple hyperechoic lines that are perpendicular to the US beam that occur deep to interfaces
