Radiography and Ultrasonography

Describe appropriate darkroom conditions as related to safelight illumination.

A darkroom light switch should have a delay to minimize any accidental light exposures. Wet and dark areas should be separated to prevent unintended exposures. The images should be processed by technicians wearing appropriate safety equipment. This includes proper gloves and protective eye wear. An eyewash bottle should be kept in the vicinity, in compliance with state/federal regulations regarding timely treatment following an accident. Light leakage is defined as an event which leads to fogging of the images in the radiographs. A check for fogging can be accomplished by placing an open, unprocessed film cassette in the darkroom. Three quarters of the film should be covered with a lightweight paper board for a period of 1 minute. The other portion of the cardboard should be covered for the second minute. The first section should be uncovered during this time. Continue in like manner, until the entire board has had 1 minute of covered exposure. This takes a total of 3 minutes time. On the fourth minute, the film is left uncovered in its entirety so that the film can be totally exposed. After development, any darkened areas on the film will indicate conditions which permit film fogging to occur.

Define: Tranducer

A device that converts one form of energy into another form. The defining features of the transducer may influence the wavelength..

Attenuation

A loss of vitality, amplitude, or power. With sound, this occurs when intensity is lost as an ultrasound beam passes through tissue. The loss can be attributed to the way the beam is absorbed into the tissue as it makes its way through. The absorption process creates heat and results in a loss of energy. Tissue that has sound refractory characteristics can scatter the sound in a multitude of directions

Define the terms resolution, lateral resolution, axial resolution, and sound beam zones as they pertain to ultrasonography.

A properly resolved (clearly seen) image on an ultrasound is defined as 2 small objects in close proximity which can be individually recognized. The frequency of the transducer is critical tot he resolution quality of the image. Resolution is increased when higher frequencies are applied. This is due to the shorter wavelength used to gain the image. Lateral resolution refers to the ability to properly resolve 2 objects that are both side-by-side and perpendicular to the beam. The beam functions to visually separate the 2 objects from each other. The degree of lateral resolution is also a function of the beam's width. Objects in parallel position to each other are best able to be identified when they are spaced farther apart than the diameter of the beam. Axial resolution is the ability to resolve 2 objects are located one above another in the beam's pathway. In this situation, greater resolution and differentiation is obtained at lower frequencies. The size and design of the transducer controls the ultrasound beam zones. The near field (aka Fresnal zone) refers to the entire area of the ultrasound beam that recedes the focal point an is most proximal (nearest) the crystal. It is characterized by a narrowing, gradually converging beam shape.

Describe the sonogaphic appearance of the bladder, prostate, and uterus.

A sonographic image of the urinary bladder is typically dark as it is fluid filled and thus is relatively anechoic. However, the bladder has a wall that presents itself as hyperechoic, and it is not unusual to find debris in the bladder that aids in visualization. In the male, the prostate can be ultrasonographically located by following the urethra to the pelvic inlet. The urethra is encircled by the prostate. The prostate is composed of 2 lobes. The prostate has an illuminated capsule in its ultrasonographic image. In the female, the uterus is evident as the organ adjacent to an enlarged bladder. The wall of the uterus is hypoechoic. The optimum time to discover an early uterine pregnancy in small animals is about 30 days into gestation. In horses, the optimum early confirmation time is around 11-14 days into the gestation period. At these junctures, the sonographic equipment should be able to detect viable embryos in their gestational sacs. However, it can often be hard to distinguish the exact number of fetuses inside the sac. This is due to the problem of superimposition and the usual presence of gas in the intestines.

Describe the purpose of a transducer and the function of the transducer crystal.

A transducer is a device that transforms one form of energy into another form. The transducer probe is the principal transforming component of the ultrasound machine. This device will transform sound waves into electrical energy, from which an image can be obtained. The sound waves produce echoes that can be received as they bounce back in return. The pulsed-wave transducer is a device that emits a short pulse of sound, and works to send and receive these signals in a patterned sequence. An additional form of a transducer probe is known as a continuous-wave transducer. This device actually utilizes 2 transducers. The first transducer sends out a constant sound wave, while the second transducer continuously receives sound waves as they echo back. Ultrasound devices function with transducer crystals to enhance the electrical energy conversion process. However, a transducer crystal cannot send and receive sound waves simultaneously. Thus, the transducer must perform these functions in an alternating pattern (unless a dual-crystal [continuous] wave transducer is used).

Define: Second

A unit of time measured in a given cycle. This measurement is applied to number the times a cycle is replicated.

Define the basics of sound waves.

A wavelength is defined as the span of distance that a wave travels in one repeating cycle. Wavelength is written in an abbreviated international symbol or notation form as the lowercase Greek letter lambda. Audible sound has a wavelength that spans a lengthier distance than the wavelength displayed by an ultrasound A transducer is a device that converts one form of energy into another form. The defining features of the transducer may influence the wavelength. A second is defined as a unit of time measured in a given cycle. This measurement is applied to the number the times a cycle is replicated. The frequency is how many ties the cycle occurred. Frequency is given the following symbol: (f). The wavelength will extend for a longer distance or increase as the frequency decreases. The frequency range for ultrasonic waves is measured at 2 to 10 Mhz. The frequency range for human auditory perception is approximately 20 Hz-20 kHz. Velocity is given the following symbol: (v). Sound velocity is defined as the speed at which a sound wave travels through a medium. The formula for velocity is given as the frequency multiplied by the wavelength.

A-Mode

Amplitude mode

Anechoic

An absence of echoes. A condition sometimes characteristic of chambers, spaces, or fluid-filled areas, where the sounds pass deeper into the tissue without producing returning echoes from that area. This produces a black image on the viewinterm-8g screen, which sometimes represents tissue saturated with fluid. Example: Fluid inside the urinary bladder

List the components of an x-ray tube and describe how they work.

An x-ray tube consists of the following components: a cathode filament, an anode plate, a focusing cup, a target, a glass envelope (within which a vacuum is created), an aluminum filter, and a beryllium window. The x-ray tube generates the photons carry the electromagnetic charge, and directs them along a targeted pathway. The cathode filament is usually made from tungsten. The tungsten filament is a coiled wire that releases electrons when heat is applied to its surface. The cathode filament is situated across from the focusing cup and the anode plate. The filament maintains a negative potential throughout the heating process. The electrons are drawn to the positively charged anode at great speed. The anode can be immobile or it can be put into a rotation. The target is described as tungsten with a copper stem. The target is fastened to the face of the anode. The entire x-ray device is encased within a tube shaped Pyrex capsule that creates a vacuum. This is essential for x-ray generation. The x-rays are sent out through a small window fashioned from a thin section of glass. This glass absorbs a small quantity of x-rays or electromagnectic radiation.

Discuss other types of transducers.

Another kind of transducer is known as the mechanical multiple angle or sector scanning transducers. The mechanical sector transducer utilizes one or more crystals in its operations. The device will create an image that has the form of a pie wedge or circle segment. It is often a better choice when deep tissue penetration and a large, far-field view is needed. Another version of a transducer is the phased array sector scanner. This computerized device has the ability to guide ultrasound pulses from about 20 crystals through a particular area. Providing images of time-motion (TM) activity, the phased array sector scanner is best applied to echocardiography. However, this compact device can be an expensive purchase. Another version of a transducer is the broad bandwidth transducer. This version utilizes a piezoelectric ceramic and epoxy material in the probe. It is a lightweight device with a minimum of acoustic impedance. Importantly, these transducers can operate on a variety of frequencies. These frequencies or short-duration pulses are available because of the transducer's ability to transmit over a wide range of bandwidths.

List the factors that influence radiographic contrast and subject contrast.

Black and white can be combined to produce a variety of different shades of gray and degrees of intensity. The degree of difference between the shades is defined as the radiographic contrast. Radiographic contrast can be impacted by the following: kilovoltage, scatter radiation, processing features, and physical aspects. Some examples of physical aspects include beam attenuation and fogging effects. Kilovoltage (kVp) has the strongest impact on radiographic contrast. The x-ray beam is polychromatic, with many wavelengths. Lower kVp ratings offer wider rangers of energy levels. Higher kVp ratings produce more consistent penetration and fewer disparities. Objects along the pathway of the beam scatter the effect. This creates a reduction in the film's contrast and is displayed by overcast shades of gray on the film. Subject contrast distinguishes between the density an mass of 2 adjacent structures. A high subject contrast will produce a more prominent radiographic contrast. The thickness and density of the anatomic structures being imaged will also impact subject density. Bones are an example of an object with high subject density, as bones are more opaque to x-rays, and will thus image as white or light gray on a radiographic image

B-mode

Brightness mode

"Cat" scan

Computerized Axial Tomography

Describe the imaging technique called computerized axial tomography.

Computerized axial tomography ("CAT" scan) is primarily employed as a diagnostic test to determine the health of the central and peripheral nervous system, although it is also used for many other kinds of evaluations. This imaging technique can detect numerous forms of disease in a variety of animas However, it is also one of the costliest examinations used by veterinarians. The animal having this procedure will require general anesthesia to limit movement. The equipment used in computerized tomography requires that the patient by moved slowly through a circular gantry while remaining virtually motionless. This circular segment of the machine holds the x-ray tube and detectors. The equipment has the capability of moving completely around the patient, encompassing 360 degrees in total Each movement of the scanner produces a recording of a single cross-sectional slices of data. This recording is created when x-rays are picked up by the scanner. The x-rays are transformed into electronic signals with a wide range of intensity levels. These varying levels are produced through radiant attenuation. The image is then computed and shown in a re0creation produced by the computer.

Describe the contrast media used in contrast radiography.

Contrast radiography allows hollow areas of the body (vessels, intestines, etc) to be more meaningfully viewed. Two variations of the contrast medium include positive and negative contrasts. The positive contrast agents are known as radiopaque agents. These agents are found in products like barium and iodine. Radiopaque agents have the capacity to absorb x-rays more thoroughly than the absorption rate found in bones. This causes the structure filled with the radiopaque agent to appear whiter on the film than any other structure in view. Barium is typically employed when examining areas of the gastrointestinal tract. This is an insoluble positive contrast agent. Soluble contrast agents are found in products with iodine. These products are appropriate for the examination of the renal, articular, vascular, myelographic, and gastrointestinal systems. It should be noted that some patients can exhibit toxic reactions to these agents, although these reactions rarely occur. Soluble iodinated contrast agents can be attributed to a hyperosmotic condition. Negative contrast agents include air and carbon dioxide, and are known as radiolucents. Radiolucent media will show up as black (indicating a void) in radiographs. This is because it is entirely unable to absorb x-rays. Both positive and negative contrast agents are employed by professional using double-contrast studies.

Describe the technique called Doppler imaging.

Doppler imaging is beneficial in examining aspects of the body that remain in constant motion. One such part of the body is blood. Doppler imaging uses differences between sound wave frequencies received at a remote point as opposed to the frequency found at the sound's origin to analyze certain characteristics about motion. The difference is most pronounced when there is activity between the original sound and the receiver. Specifically, the sound wave frequency can increase when the receiver is moving towards the originating location of the sound, and it can decrease when the receiver moves away. Thus, the frequency will increase or decrease in relationship to any movement between the receiver and the originating source. The postion-dependent wave amplitude changes between a stationary object and one in motion are referred to as a "Doppler shift." In Doppler imaging, a continuous-wave ultrasonic beam is sent to and received back from a part of the body in motion. Using the sound wave frequency data obtained from movement such as blood flow, the blood's velocity can be calculated. Doppler imaging is beneficial in determining whether or not a lesion or a mass exists in a vessel. Doppler imaging can also help in location portal systemic shunts and in assessing cardiac function and effectiveness in the body, etc.

Describe the various screen speeds and characteristics of screen film.

Fair to goo resolutions can be obtained with medium-speed x-ray films. These require relatively low exposure times. Fast-speed films allow more reduced exposure time and provide superior patient x-ray penetration. However, they trade speed for image quality. The poorer quality image is caused by the larger crystals and thicker layers applied in fast-speed screens. These blurred images show less detail than images taken with a medium or slow speed screen. Film made with silver halide crystals or grains has a superior rate of sensitivity to the waves of light produces from the intensifying screens. This increased sensitivity allows a diagnostic radiograph to be created using a shorter exposure time. Greater resolution is obtained because of the finer image resolution grains on the film. This greater resolution is accomplished through longer exposure times. Shorter exposure times can only be achieved with larger grains on the films. The veterinarian will find that x-rays performed on animals usually require only a medium-grain film. This medium-grain film is a concession made to obtain a reasonably good image resolution without an extended exposure time.

Hypoechoic

Giving back few echoes. A condition where less sound echoes back to the transducer, as compared with adjacent tissue. This less reflective tissue creates a darker ultrasound image. Examples: muscle as compared to tendon fiber, soft atherosclerotic plaque, and some tumor tissue.

Define: Frequency

How many times the cycle occurred. Abbreviated as (f). Wavelength will extend for a longer distance or increase as frequency decreases. Frequency range for ultrasonic waves is measured at 2-10 MHz. The frequency range for human auditory perception is about 20 Hz - 20 kHz.

Describe the imaging technique called nuclear scintigraphy.

In nuclear scintigraphy imaging, the patient can be given gamma emissions from radioactive material or radionuclides applied by a variety of methods. These methods include intravenous injections, transcolonic applications, or aerosol insufflation (blown into or onto the body). The radioactive material is picked up by sensors found in the gamma scintillation camera. The organ is then pictures on x-ray film, formatted in black and white shades of varying contrast. Clinical nuclear scintigraphy is typically performed on the thyroid, bone, and iver. The results derived from this technique provide physiological, pharmacological and kinetic data. Nuclear scintigraphy is beneficial in many treatments to provide to horses. However, the handler and persons coming into contact with the horse having this procedure should use the recommended safety equipment. This equipment should prevent undue exposure to the harmful effects of radioactive material. The animal will expel the radiopharmaceutical elements in its bodily waste. The contaminated urine and feces is normally expelled within 24 to 72 hours after the procedure was completed.

Define the term attenuation artifacts.

Include acoustic shadowing and acoustic enhancement. Acoustic shadowing is found when an object reflects a sound wave in its entirety, producing an acoustic shadow of the actual structure. Acoustic enhancement occurs when a propagated wave passes largely unimpeded through an anechoic structure, resulting in an artificially strong wave and echo from otherwise deeper tissues.

Define: Audible sound

It has a wavelength that spans a lengthier distance than the wavelength displaced by an ultrasound.

MRI

Magnetic Resonance Imaging

Describe the imaging technique called magnetic resonance imaging.

Magnetic resonance imaging (MRI) produces cross-sectional images of anatomy. This technique has some shared characteristics with those found in computerized axial tomography. However, magnetic resonance imaging does not employ the use of ionizing radiation to create a likeness of the tissues or organs. Instead, it incorporates a magnetic field to produce the desired image being scanned. Enclosed coils in the device are able to transmit and receive magnetic field signals. Then the computer organizes those signals into an image. Magnetic resonance imaging provided an image resolution that has a better quality than other techniques used. Indeed, thus device is sensitive enough to display detailed portions of an animal's anatomy and tissue makeup. Magnetic resonance imaging particularly lends itself to head and spine appraisals that require more intricate images to be produced.

Describe the process for automatic film processing.

Mechanized film processors can be employed to provide automated film processing. The film is routed through the chemical solutions and out to a dryer on a roller assembly. The temperature ranges from 20 to 35 degrees celsius (77-96 fahrenheit). Mechanized film processing can take as little as 90 seconds or as long as 8 minutes. The procedures and chemicals are much like those used in the manual processing methods. However these mechanical chemicals are mixed in a much more concentrated manner. The hardener is mixed directly into the developer solution. These is no rinsing step between the developing and fixing steps in this method. The mechanical process can only be accomplished by maintaining very clean equipment. The rollers, roller racks, and crossover rollers cannot be dirty. Chemicals should be replaced at recommended intervals to give optimum performance in the mechanized film development process.

M-mode

Motion mode

Describe the different types of transducer crystals and the function of the linear array transducer.

Natural crystals are often utilized as transducer crystals. These crystals include: quartz, tourmaline, and Rochelle salts.. Some synthetic crystals are also utilized as transducer crystals. Synthetic crystals include the following: lead zirconate titanate, barium titanate, and lithium sulfate. Sound vibrations are promoted via a piezoelectric electric effect. A dampener is applied to terminate the vibrations after they have been received. Then new echoes received come into contact with the crystals and initiate the vibration again. These vibrating movements back and forth are subsequently transformed into electrical energy. One version of transducer is known as the linear array transducer. The linear array transducer has a tiny row of crystals that operates in a regular rhythm. The linear array transducer produces a composite image from many parallel lines. These lines form an image in a rectangular shape. Thus, the linear array transducer is often best applied to imaging a wide, near field such as transrectals and equine tendons.

List the basic criteria and principles used for positioning and restraint when taking diagnostic radiographs.

Non-manual restraint of an animal is always recommended because of its minimization of radiation exposure for staff. Calipers are measuring instruments used to determine the number of centimeters involved in an area to be radiologically exposed. The recommended views are taken from 2 right angles. However, this is not true for thoracic views, contrast studies, equine radiography, and injuries that present only one view option. It is best to achieve a close up shot with the film nearest to the subject as is workable. The beam should be centered over the specified portion of the body. The film is positioned in a parallel direction. The x-ray beam is set perpendicular to the portion of the body to be shot. Some accommodation may be necessary for certain anatomy parts. This accommodation may be in the form of collimating (bringing into a direct line) the machine to use the smallest field available. Extremities are shot with the proximal and distal joints of long bones included in the image. The patient may need to be repositioned to get the best view. It is best to take the time necessary for repositioning so that retakes will not be required.

List the characteristics of non-screen film and describe appropriate darkroom conditions.

Nonscreen x-ray film does not utilize intensifying screens. It has improved sensitivity to direct ionizing radiation. However, the nonscreen film will require a longer exposure time to work. Even so, it has the advantage of producing an image that has better detail-revealing resolution than that of an image gained via an intensifying screen. The film is packaged into a heavy envelope that does not allow light to pass through. This film is often used in dental offices, where the bulkiness of radiographic film coupled with an intensifying screen is prohibitive. The film speed is depicted by the label D or E. The faster nonscreen film speed is the E label. Proper darkroom conditions must also be maintained in clean, well ventilated, temperature-controlled facilities. The correct wattage should be used for a safelight. A filter for the safelight that matches the sensitivity of the film being developed should also be utilized. The light should be positioned at least 4 feet away from the work space.

Describe the attenuation artifacts that can occur in ultrasound images.

Posterior shadowing occurs when an object blocks sound waves from passing deeper into the body. This type of shadowing can be a results of calculi and/or gas in the intestines. Calculi are defined as stones or hard fragments that are formed in the kidney, gallbladder, or urinary bladder. Objects located on the backside of organs filled with fluid may present with enhanced echoes, when compared to adjacent objects or tissues. This enhancement is a result of a fluid's anechoic nature, allowing sound waves to more readily pass through, and thus resulting in acoustic enhancement. Attenuation artifact occurs when tissues in the near field reduce the intensity of the ultrasound beam, leaving tissues in the focal region and far field poorly imaged. Attenuation artifact may cause a lesion itself to be perceived as a hypoechoic mass or cyst. Hypoechoic conditions exist when certain tissues direct less sound back to the transducer than adjacent tissues. This less reflective tissue creates a darker appearance than the neighboring tissue. Examples include muscle compared to tendon fiber, soft atherosclerotic plaque, and some tumor tissues.

List some pointers for manually processing film.

Processing of film involves the following steps: developing, rinsing (in a stop bath), fixing, washing, and drying. The chemicals must be diluted and mixed according to the manufacturer's directions. The chemical solutions are mixed at a temperature of 20 degrees C or 68 degrees F. The manufacturer lists detailed information about the time-temperature development of each chemical. The film should be shaken at regular intervals to prevent any air bubbles from forming while in the developing fluid. The oxidation of developing chemicals can be reduced by keeping lids secrely fastened on the tanks. As the developer solution is used, the exposed silver halide crystals are changed to black metallic silver. If the expected density or contract does not appear, then the solution has weakened and should not be used. The fixed solution is used to remove unexposed, undeveloped silver halide from the image. It also hardens the film. It should be discarded if it takes longer than 2 or 3 minutes for this step to be completed. The process is finished when the image goes from a hazy, cloudy image a clear image.

Discuss the maximum permissible dose of radiation and the hazards associated with radiation.

Radiation exposure standards are set to ensure patient and staff safety. The maximum radiation exposure allowed is defined in terms of dose rates and exposure time (dose = dose rate x exposure time). Thus, the maximum exposure time permitted is a function of the environmental and occupational dose rate. In clinical settings, the criteria are set according to guidelines issued by the National Committee on Radiation Protection and Measurements (the NCRP) These are derived from the recommendations produced by the International Commision on Radiological Protection (the ICRP). The NCRP, and almost every state, has established radiological protection guidelines. These guidelines specify acceptable rates of exposure when, for example, one is holding an animal for an x-ray (some states prohibit any type of manual animal restraint). To provide an extra measure of protection, staff will wear an individual dosimeter at the work site. It provides a cumulative record of radiation exposure over time, and is evaluated by a federally approved laboratory on a routine basis.

List some safety practices when taking radiographs.

Radiation treatments cannot be conducted when a pregnant person is present in the room. It is best to use non-manual restraints on the patient, even if the state allows manual restraints, to avoid unnecessary x-ray exposure. People in the room should wear the following: protective gloves, thyroid protectors, and aprons. The x-ray machine itself should not be handled without protection. It is necessary to use a 2.5 mm aluminum filter to eradicate the lower-energy portion of the x-ray beam. The x-ray machine required routine maintenance and calibration It is important to keep body parts out of the path of the primary beam. This is necessary because of the primary beam's ability to transmit 25% of its radiation through a body shield. The technician should wear a dosimeter next to the outside collar of the apron. Ideally, diagnostic radiographs will be achieved with the fasted (lowest dosing) film-screen systems employed by the attending technician.

List the factors that influence radiographic density.

Radiographic density ultimately relates to the degree of darkness or blackness present on the developed film's surface. The density level is directly correlated with the number of photons that have affected the film. The density can vary according to the total number of x-rays that come into contact with the intensifying screen, transferring the image to the film. It can also be altered by the penetration strength of the x-rays. Density can be further influenced by the development time and temperature. Focusing filters and grids can make the beam weaker. In addition, tissue density and patient coverings and support pads can lessen the strength of the beam. The beam strength and exposure duration is measured in milliampere-seconds of x-rays that come into contact with the intensifying screen. The more x-rays that come into contact with the intensifying screen (a function of both strength and time), the more densley activated (darkened) is the film. The strength of penetration is determined by the measurement of kVp (kilovoltage peak). The higher kVp settings produce higher energy x-rays. These higher energy x-rays have higher levels of penetration strength. This results in an improved film density. Thicker or denser tissue causes a reduced film density (lighter film). In like manner, thinner tissue causes an increase in film density (darker film).

Define the term propagation artifacts.

Reverberations, refraction, and mirror images. Reverberations are exhibited as linear echoes. Reverberations are a result of sounds reflected between a strong reflector and the transducer in a continuous pattern. An example of a strong reflective (reverberation-prone) surface is illustrated by bones. Refractions are a result of sound beams changing directions as they are bounced off one medium and strike another medium's surface. Refractions are to blame for the manifestation of organs in unusual positions. An example of this is when an image is duplicated and appears as if it exists on both sides of a reflecting axis. This phenomenon is often due to the close proximity of strongly reflective organ to the reflector. This is typical occurrence in ultrasound images taken of the liver and of the diaphragm.

Isoechoic

Similar amplitude wave returns. Areas of similar echogenicity are considered to be isoechoic to each other.

Sonolucent (Echolucent)

Something that does not reflect sound, and thus produces no echo.

Define: Velocity

Sound velocity is defined at the speed at which a sound wave travels through a medium. Abbreviated as (v) Formula: v = f x (lambda) or velocity equals frequency multiplied by the wavelength.

Hyperechoic

Strong echo reflection. Also, a greater amplitude wave return. The results is a whiter image appearance from the high degree of sound that is transmitted back to the transducer. Examples: Bone, tendons, and ligaments when perpendicular to the beam.

Describe additional display formats used for ultrasound images.

The brightness mode (B-mode) produces a two-dimensional map of data represented by dots or small marks on a graph. The dots represent the returning echo. The deepness of the mirrored image is indicated by the location of the dot on the graph's baseline. The baseline is used to reference the results found. The motion mode (M-mode) is represented by a one-dimensional wave graph. It's vertical axis indicates the immediate position of the moving reflector. The horizontal axis represents the time. Objects in motion are represented by wavy lines on the graph. Stationary or immobile objects are represented by straight lines on the graph. The M-mode is best applied for cardiac examinations on a patient. The M-mode provides a beneficial evaluation of the condition of cardiac valves, walls, and chamber sizes. These display formats are essential to the ultrasound's ability to provide a display that meets the criterion for each particular purpose sought by the technician obtaining the image.

Acoustic Impedance

The capability of something to withstand or resist sound conduction. The density of tissue may be reflected in its degree of impedance. However, both air (not dense) and bone (very dense) will significantly obstruct the passage of sound. Thus, both bone and air have a high rate of acoustic impedance, despite their widely differing density. On a while, however, tissues respond favorably to the passage of sound waves. Therefore, most bodily tissues have a low rate of acoustic impedance.

Time period

The equivalent of one cycle of the wave. This is given the symbol (T).

Describe the sonographic appearance of the heart.

The heart is visualized using 2 types of sonographic imagery. M-mode or two-dimensional B-mode imaging. Sonograms of the heart require that 2 seperate directional views be taken along both the long- and short-axis of the organ. The Doppler imaging technique can then be applied to determine the turbulence and velocity of red blood cells within the heart. For an echocardiogram (cardiac sonogram), the animal should be placed in lateral recumbent position. The heart is normally ultrasonographically examined by aiming the ultrasound transducer between the fourth and fifth ribs. In this way, it is possible for the transducer beam to reach the heart from the underside of the animal. A hyperechoic appearance is seen in the walls and valves of the heart. A hyperechoic condition results when the tissue or an organ (or parts thereof) are highly refective of an ultrasound beam, thus producing a brighter or whiter appearance on the ultrasound image than the surrounding tissue.

Amplitude

The intensity or height of a wave.

Describe the sonographic appearance of the liver, gallbladder, and kidneys.

The largest part of the spleen is hyperechoic. It has a standard granular profile. It is also surrounded by an illuminated capsule. The patient's spleen should be ultrasonographically imaged from the left side. This side provides the best option for examining the spleen, with the least amount of surrounding tissue interference. The spleen lies just below the skin and facia, behind the stomach and under the diaphragm. Viewing the spleen from the trailing edge of the liver provides important imaging advantages. The livers outer layer has a thick surface which presents an echogenic disparity that should be avoided. The gallbladder (or cholecyst) is located under the liver. The liver has a multitude of vessels and bile channels. Sonographic images of the gallbladder are displayed as anechoic, as it is largely fluid (bile) filled. Thus, it presents itself as an illuminated wall. Sludge or solid deposits can occasionally be found and visualized in the gallbladder. Animals that have not eaten before a sonogram often have large (dilated) gallbladder sonographic images. The kidney will present as ovoid or egg-shaped. It will be enclosed by an illuminated capsule, as the cortex of the kidney is hyperechoic. The medulla of the kidney presents itself an anechoic. The pelvic fat will be displayed as an illuminated central zone. The sagittal view should be measured to determine the size.

Describe the terms associated with the sound beam zones and display formats used for ultrasound images.

The near field is that portion of the ultrasound beam that is closest to the crystal. The narrowest position or spot that is reached is known as the beam's focal point. The shifting of the focal point closer to the image can produce a better resolution of the image The transducer can be brought into focus by "shaping" (manipulating) the crystal. The focus can also be improved by adding a lens to the transducer. The section of the beam that gets broader, and less intense, as it moves away from the focal point is known as the far field (also called the Frauhnhofer zone). The different display formats for the ultrasound images include amplitude mode, brightness mode, and motion mode. The amplitude mode is abbreviated as A-mode. It can provide the depth and dimensions of a target. A-mode is demonstrated as a one-dimensional graph with a succession of rising points. Each rising point stands for a returning echo. A point that is higher on the graph is indicative of a larger, more intense echo coming back.

Describe the responsibilities and hazards involved in radiation safety.

The practice owner should be responsible for applying the appropriate radiological safety procedures in accordance with state requirements. These guidelines involve the use of the dosimeter devices, efficient radiation detection devices, equipment registration, staff certification, and radiologically appropriate room design. The health department is normally responsible for regulating these devices and safeguards. Trained personnel are necessary to apply to appropriate radiation safety guidelines. Personnel must be able to use the devices correctly according to instructions received. Every cell in an organism can be affected by ionizing radiation. Ionizing radiation generated charged particles that are able to modify or disintegrate a molecule. Modified molecules may not perform their intended functions appropriately. This can dangerously interrupt the normal functioning of tissues. This harm may not be immediately apparent. Some effects do not become evident for hours, days, months, years, or even generations. Intergenerational delays may occur when damage presents itself only in the genetic makeup of reproductive cells. Other alterations may not be readily apparent because of concurrent tissue restoration. Even so, somatic cell damage may take place throughout the body. The region of the cell most susceptible to the effects of ionizing radiation is the nucleus, and those aspects central to cellular reproduction.

Describe the sonographic appearance of the stomach, bowel, pancreas, and adrenal gland

The presence of gas or flatus in the abdomen and intestines presents a routine obstacle in ultrasonography. This is because air is hyperechoic and thus intestinal flatus limits the imaging of anything in the far field behind it. Even so, the intestinal walls on a sonographic image will look white or dark grey on the screen. Depending upon its contents, the stomach may be hypoechoic. However, the rugal folds of the stomach are usually visible in the image created. The pancreas is sandwiched between the spleen and the stomach. It is adjacent to the duodenum. The pancreas is a digestive and endocrine gland found in the body. The adrenal gland appears as a standard (isoechoic) gray color. The adrenal gland is responsible for the secretion of hormones in the body. The adrenal gland itself is hypoechoic. As reference points, the cranial pole of the kidney is situated toward the middle of the adrenal gland. The renal artery is next to the caudal pole found in the adrenal gland. The rental artery connects to the aorta.

Define: wavelength

The span of distance that a wave travels in one repeating cycle. Abbreviated by lambda.

Describe the intensifying screens and screen speeds used in x-ray film.

The x-ray machine incorporates an intensifying screen made from a synthetic base covered in sheets of small luminescent phosphor crystals. These crystals function as a protective covering. Two intensifying screens are located on the interior fabric of the x-ray cassette. The film is packed in between these 2 screens. Visible light exposed the light-sensitive emulsion of the x-ray film when radiation connects with and illuminates the surface of the phosphor crystals. This is referred to as indirect imaging, and is responsible for more than 95% of the film's exposure to light. The screen functions to decrease the exposure time necessary to create a diagnostic image on film. Differences in intensifying screen speeds refer to the amount of exposure time required for the production of a diagnostic film. Screen speeds are measured as slow, medium, and fast. The best quality image is gained when slower speeds are used. Further, slower screen speeds do not have any significant problems relating to exposure times. Gradually, computerized x-ray machines are moving into the field. Relying on digital media, they are much more versatile to use, and they bypass the film development step altogether. Further, they have greater file-sharing and archival capacities. Thus, they are slowly replacing the older film and intensifying screen-based processes. In the interim, however, familiarity with traditional x-ray equipment remains important.

Describe the components of an x-ray machine.

The x-ray machine must include the following components: electrical circuits to control the x-ray tube, a control panel, and a tube stand. It has filters, collimators, and grids as a part of its framework. The electrical circuits utilize high-voltage electricity to generate energy and speed. This speed allows the electrons to develop a high electromagnetic potential. The electrical circuits also supply a low-voltage electric current used for heating the cathode filament. A timer switch operates to measure exposure time in seconds. The rectification circuit is used to change the current supplied to the tube from alternating to direct current. The control panel is utilized to manage and regulate the kilovoltage peak, milliampere, milliampere-seconds, and/or seconds. This regulation is dependent upon the capacity of the x-ray machine. The kVp potential establishes the class of energy. The mA (milliampere) and involved tie establishes the intensity of the x-rays. The x-ray tube is set up on a foundation known as the tube stand.

Echogenic

Tissues with the capacity to produce return echoes. These echoes are singled out by the transducer, and displayed in a black and white image (with varying gray tones) that represents these tissues. Organs in proximity to each other will produce a larger echo reflection, indicating the gap between each organ.

Define x-rays and how they are produced.

X-rays are derived from the energy produced by electrons or negatively charged particles within an atom. This energy is converted to electromagnetic radiation. The radiation produces energy particles known as photons. Photons do not have any mass or electrical charge, but they can carry electromagnetic (EM) energy. When EM-carrying photons crash into and pass through matter, the x-ray picture is created. An x-ray tube has filters that are able to direct the source of the electrons at the object toward which it is aimed. The x-ray tube must have the following components: a source of electrons, a method to accelerate the electrons, a defined path, a target, and an encompassing envelope in which to create a vacuum. The electrode pair (a heated cathode and an anode carrying a powerful voltage charge) is the source from which the EM-charged photons are derived. The cathode is capable of releasing electrons when subjected to heat. The electrons are sped up when drawn toward the charged anode, and their collision with the anode produces EM-charged photons, which are aimed to produce a collision with the intended target. Approximately 99% of the energy created is heat and 1% is x-rays (photons carrying EM energy). EM energy is measured as a kilovoltage peak or potential kVp. This energy can be harnessed and adjusted in accordance with the specifications of the particular x-ray machine. The kVp of the electrons establishes the penetration strength of the x-rays.