Ultrasound physics

Ultrasound frequencies in diagnostic radiology range from:

2 MHz to approximately 15 MHz.

Ultrasound frequencies range from __________to__________, although even higher frequencies may be used in some situations.

2 to 15 MHz

useable frequency range in diagnostic medical sonography

2-20 MHz

Ultrasound transducers contain more than one operating frequency. The following frequencies are a guide to frequencies typically used for ultrasound examination: 2.5 MHz: 3.5 MHz: 5.0 MHz: 7.5 MHz: 10.0 MHz: 15.0 MHz:

2.5 MHz: deep abdomen, obstetric and gynecological imaging 3.5 MHz: general abdomen, obstetric and gynecological imaging 5.0 MHz: vascular, breast, pelvic imaging 7.5 MHz: breast, thyroid 10.0 MHz: breast, thyroid, superficial veins, superficial masses, musculoskeletal imaging. 15.0 MHz: superficial structures, musculoskeletal imaging.

right posterior oblique

A patient lies at a 45 degree angle on their right posterior side. This is the _________ _________ _______ position.

acoustic enhancement

Acoustic enhancement also called posterior enhancement or enhanced through transmission, refers to the increased echoes deep to structures that transmit sound exceptionally well. This is characteristic of fluid-filled structures such as cysts, the urinary bladder and the gallbladder. The fluid only attenuates the sound less than the surrounding tissue. The time gain compensation (TGC) overcompensates through the fluid-filled structure causing deeper tissues to be brighter. Simply it is seen as increased echogenicity (whiteness) posterior to the cystic area. The presence of acoustic enhancement aids in the identification of cystic masses but some solid masses, especially lymphoma, may also show acoustic enhancement posteriorly.

___________ ____________ is present behind bones, calculi (stones in kidneys, gallbladder, etc.) and air (intestinal gas)

Acoustic shadowing

___________________ in ultrasound is the reduction in amplitude of the ultrasound beam as a function of distance through the imaging medium. Accounting for _________________ effects in ultrasound is important because a reduced signal amplitude can affect the quality of the image produced.

Attenuation

Blood vessels have a distinct appearance on color __________ mode: flow toward the probe appears red, while flow away from the probe appears blue. A useful mnemonic used by radiologists is BART, i.e., ______ ______, ______ ______.

Doppler; Blue Away, Red Toward

________________ refers to a structure with dissimilar components or elements, appearing irregular or variegated. For example, a dermoid cyst has heterogeneous attenuation on CT.

Heterogeneous

phased array probe uses

Phased Array transducer has a small footprint and low frequency (its central frequency is 2Mhz - 7.5Mhz). The beam point is narrow but it expands depending on the applied frequency. Furthermore, the beam shape is almost triangular and the near-field resolution is poor. What can you use the Phased Array transducer for? Cardiac examinations Abdominal examinations Brain examinations

Blood vessels often appear black or anechoic . Veins are usually easily collapsible upon external __________ by the transducer, while arteries are pulsatile and do not collapse with moderate pressure.

Pressure

proximal

Proximal means nearer to the center (trunk of the body) or to the point of attachment to the body.

read zoom

READ zoom produces the worse kind of images because it relies on stored images which enlarges the pixel density in that region

Refraction artifact

Refraction artifact can occur when a transmitted ultrasound pulse strikes an interface at a non-perpendicular angle. The difference in propagation speeds between the two tissues can cause refraction to occur. Should the refracted incident sound wave strike a reflector and cause an echo to return to the transducer, this may be displayed at an incorrect location as the transducer assumes all echoes have traveled along a direct path. Refraction artifact should resolve if the transducer is moved such that the incident pulse is perpendicular to the interface.

depth

The Depth is special a knob for adjusting the distance of the field of view. Structures within the field of view can be moved far or closer by adjusting the Depth. This is to ensure that the region of interest is closer enough for optimum visualization.

dynamic range

The Dynamic Range is a control on the ultrasound system that allows the operator to determine the range of shades of gray to be displayed on the monitor. Broad shades of gray displays a wider range of echo-intensity between bright and dark and produces a smoother image overall, whilst narrow shades of gray displays a narrower range of echo-intensity between bright and dark and produces a higher contrast between two regions of different echogenicity.

What is a homogeneous echo pattern?

The appearance is of a compact mesh of fine scattered echoes of uniform distribution and amplitude.

zoom

The zoom is used for magnifying the area of interest. Unlike the depth which magnifies by moving the area of interest closer, the zoom actually magnifies by making the region of interest appear bigger. Another limitation of the depth that is addressed by the zoom is the ability to enlarge a specific region of interest. Without using the zoom, measuring some tiny structures may difficult because of poor spatial resolution. For instance, in measuring the thickness of the gallbladder wall, using the zoom improves the visualization of the wall for an accurate measurement

Isoechoic

Tissue or structures which produces an echo of the same strength as that of the surrounding structures or tissues, making it difficult to isolate.

linear array probe

Ultrasound probe with multiple in-line transducers that produce a rectangular shaped image.

write zoom (RES)

WRITE zoom tries to maintain the pixel density by zooming the image live which produces a better spatial resolution... regional expansion selection.

doppler effect.

a moving object will change the frequency of sound passing through it. This is how one can produce the color doppler mode (BART)

left lateral decubitus

a patient lies on their left side. This is the _______ _______ _______ position.

Acoustic impedance (Z)

a physical property of tissue. It describes how much resistance an ultrasound beam encounters as it passes through a tissue.

Echogenic

ability to bounce an echo... Echogenicity is higher when the surface bouncing the sound echo reflects increased sound waves.

If the difference in tissue density is very different, then the sound is completely reflected, resulting in total __________ __________

acoustic shadowing.

focal zone

allows the operator to improve lateral resolution in a region of interest by adjusting the focal zone. This is an additional measure to minimize the effect of attenuation. However, while other controls such as the overall gain and TGC are effective for improving axial resolution, adjusting the focal zone is much more effective for improving lateral resolution. Lateral resolution refers to the ability to identify structures lying side-by-side as separate structures, while axial resolution refers to the ability to identify a structure lying on another structure as separate structures. The focal zone normally appears at the lateral side of Bmode as a triangular-shaped structure or a dot. It can be moved up or down by the operator and should be placed at the region of interest or posterior to that region

period

amount of time one cycle takes to occur

The amplitude and intensity of ultrasound waves decrease as they travel through tissue, a phenomenon known as ________________

attenuation

Ultrasound transducers contain a range of ultrasound frequencies, termed ____________. For example, 2.5-3.5 MHz for general abdominal imaging and 5.0-7.5 MHz for superficial imaging.

bandwidth

large Bone appears __________ or anechoic on US, with a bright hyperechoic rim. Because the US beam cannot penetrate bone, it casts an acoustic shadow beyond it. Smaller bone is bright throughout.

black

celiac axis location

branches off of the aorta (superior to superior mesenteric artery)

B mode/ Greyscale imaging

brightness mode. pixels range from black to white (commonly used)

A hypoechoic nodule, sometimes called a hypoechoic lesion, on the thyroid is a mass that appears __________ on the ultrasound than the surrounding tissue.

darker

when an ultrasound beam passes through muscle tissue and encounters bone, it reflects off of it due to the difference in ____________ between the tissues.

density

Based on ________________, a structure can be characterized as hyperechoic (________ on the screen), hypoechoic (________ on the screen) and anechoic (_________ on the screen)

echogenicity; white; grey; black

distal

farther from the origin of a body part or the point of attachment of a limb to the body trunk

__________x__________ = velocity through a medium. Because we're shooting ultrasound through a body cavity which contains blood, muscle, fat, bone, etc., the speed will vary through these different tissues.

frequency x wavelength

6 basic controls to adjust on an US machine (instrument)

frequency, focus, depth, gain, TGC, zoom

propagation speed

how fast sound waves move through a medium... speed of sound in soft tissue is always 1540 meters/second or 1.54 mm/microsecond

The appearance of nerves is variable, depending on the proximity to the neuraxium. Proximal nerves are hypo-anechoic (approximately similar to blood vessels but neither collapsible nor pulsatile), and distal nerves are __________________, with a stippled ("honeycomb") structure (with hypo-anechoic fascicles on the hyperechoic background of connective tissue surrounding them)

hyperechoic

Muscles are ------echoic with striate structure; fat is almost anechoic, while fascia and other connective tissue strands and fascicles appear as hyperechoic lines. Lymph nodes appear ____________ or _____________.

hypoechoic; anechoic or hypoechoic

Something with low echogenicity appears dark in the image and is called ___________, while something with high echogenicity looks light and is called _____________.

hypoechoic; hyperechoic

Ultrasound waves are reflected at the surfaces between the tissues of different density, the reflection being proportional to the difference in _______________

impedance

If the speed of sound increases, then impedance __________

increases.

if the density of a tissue increases, impedance ________________

increases.

curvilinear probe

large footprint that allows good near-field and far-field visualization with limited intercostal access

refraction artifact degrades

lateral resolution

________ frequencies are used for deeper body structures

low

The ultrasound beam originates from __________ ___________of numerous crystals in a transducer, which is excited by electrical pulses. The transducer converts one type of energy into another.

mechanical oscillations

M mode

motion mode. often used in echocardiograms. A motion that passes through a given line on the screen will be recorded at intervals of time.

linear probe uses

near-field resolution is good... a linear transducer for 2D imaging has a wide footprint and its central frequency is 2.5Mhz - 12Mhz. You can use this transducer for various applications, for instance: Vascular examination Venipuncture, blood vessel visualization Breast Thyroid Tendon, arthrogenous Intraoperative, laparoscopy The thickness measurement of body fat and musculus for daily health care check and locomotive syndrome check Photoacoustic imaging, ultrasonic velocity change imaging

The ______________ is the functional parts of an organ, or of a structure such as a tumor in the body. This is in contrast to the stroma, which refers to the structural tissue of organs or of structures, namely, the connective tissues.

parenchyma

supine

patient is laying horizontally on their back

prone

patient is laying horizontally on their stomach

The _________________ effect is the cornerstone of traditional ultrasound. This is an electromechanical property of certain materials like quartz where an electrical current applied through the object generates vibrations resulting in pulsed sound waves.... In turn, echos reflected back on the crystal generate changes in electrical resistance and current. In short, the conversion of electrical energy (a current applied over a voltage) to mechanical energy (sound waves) is the key!

piezoelectric

When an electric current is applied to a _______________ crystal, it starts to vibrate and these vibrations generate sound waves with frequencies between 1.5 and 8 MHz (i.e ultrasound). Thus, _______________ crystals can convert electric currents into ultrasound waves.

piezoelectric

The ultrasound waves (pulses of sound) are sent from the transducer, propagate through different tissues, and then __________ to the transducer as __________ _________. The returned echoes are converted back into electrical impulses by the transducer crystals and are further processed to form the ultrasound image presented on the screen.

return; reflected echoes

It is important to remember that higher frequencies of ultrasound have __________ wavelengths and are absorbed/attenuated more easily. Therefore, ___________ frequencies are not as penetrating. This explains why high frequencies are used for superficial body structures.

shorter, higher

intercostal

situated between the ribs.

curvilinear probe uses

the beam shape is convex and the transducer is good for in-depth examinations. the convex transducer for 2D imaging has a wide footprint and its central frequency is 2.5MHz - 7.5MHz. You can use it for: Abdominal examinations Transvaginal and transrectal examinations Diagnosis of organs

Acoustic impedance (Z) depends on:

the density of the tissue (d, in kg/m3) x the speed of the sound wave (c, in m/s)

wavelength

the distance of one cycle

frequency

the number of cycles (wavelengths) that occur per unit of time (seconds). Measured in hertz

A way to overcome ultrasound attenuation is by using the _______ __________ ________(TGC) controls

time gain compensation

phased array probe

to work in small space, (lungs, or heart), short foot print

three layers of the artery

tunica interna, tunica media, tunica adventitia/externa

define anechoic (or sonolucent)

without an echo or appearing. without echoes. black on ultrasound scans.