image production v3

Which substance is added to the x-ray tube housing to increase heat dissipation?

Oil (The x-ray tube housing is filled with oil to help with heat dissipation, as well as electrical insulation. Liquid nitrogen, water, and methane have boiling points that are lower than that of oil, and are therefore not effective coolants at the temperatures generated at the anode.)

Which post-processing techniques may be used with digital imaging? (Select the three that apply.)

-Electronic masking. -Filtering. -Smoothing (Electronic masking is one word for post-exposure collimation. Smoothing refers to low-pass filtering, which removes high-frequency noise. Filtering, which may refer to high- or low-pass filtering, averages pixel strength. ABC is used in fluoroscopy. Quantum noise is seen in digital imaging, but is not a post-processing technique.)

Which factors affect spatial resolution in digital imaging? (Select the two that apply.)

-Greater number of pixels. -Smaller pixels. (Smaller pixels and a greater number of pixels increase spatial resolution. Bit depth affects contrast resolution. A smaller matrix size and increased pixel pitch decrease spatial resolution.)

Assuming that automatic exposure control is to be used, what backup milliampere-seconds (mAs) are sufficient for a large (100 kg) adult anteroposterior (AP) lumbar spine done at 80 kilovolts peak (kVp)?

100 mAs. (The rule of thumb suggests a back up mAs 50% larger than the highest expected mAs. Experience teaches that it is never a bad idea to use extra back up mAs, as it is difficult to predict the influence of musculature and pathology on a lumbar spine image. Thus 100 mAs is the best choice. 40 mAs might reasonably be expected to be the minimum mAs used for the actual exposure, not backup. 60 mAs might reasonably be expected to be needed for muscular or heavily arthritic patients. Thus 50% more than the highest expectation is 90 mAs. So 80 mAs, by that reasoning, is too low.)

The collimator light must be aligned to the radiation field to within what percent of the source to image distance (SID)?

2%. (The light field must be congruent with the radiation field to within 2% of the SID. The rest of the answers fall outside this range.)

A radiograph of optimal density is produced at 15 milliampere seconds (mAs) and a source to image receptor distance (SID) of 40 inches. Which mAs value is required to produce the same radiographic density if this exam is repeated at an SID of 48 inches?

22 (The density maintenance formula, mAs1/mAs2 = D1 squared/D2 squared, provides a method of compensating for changes in SID. In this instance, 15/x = (40)2/(48)2; 1600x = 34,560; x = 34,560/1600 = 22 mAs. The other answers result from math errors.)

Which milliampere seconds (mAs) value should be selected for a patient measuring 30 centimeters if 22 mAs is optimal for a patient measuring 25 centimeters?

44 mAs. (When using fixed kilovolts peak techniques, an increase in patient thickness of 4 to 5 cm requires that the mAs be increased by a factor of 2. In this example, an increase of 5 cm would require in increase from 22 mAs to 44 mAs. The other values represent increases of 25%, 40%, and 80%, respectively.)

An image of the abdomen demonstrates appropriate density and scale of contrast, but motion blur is present due to peristalsis. If the original image was obtained with a 200 milliampere (mA) station and an exposure time of 0.35 seconds, which set of technical factors will produce a comparable exposure while minimizing motion artifact?

500 mA and 0.14 seconds. (According to the reciprocity law, an increase in mA with a compensatory decrease in time will produce the same radiographic density while reducing the effects of involuntary motion. In this instance, a 500 mA station and an exposure time of 0.14 seconds will produce the same mAs (density) at less than half the exposure time. An mA of 400 at 0.35 seconds represents an increase in mAs with the same exposure time.An mA of 300 at 0.23 seconds will produce the same density, but is more likely to result in motion blur than a time of 0.14 seconds. An mA of 100 at 0.7 seconds will produce the same density, but with a greater likelihood of motion blur.)

This mobile chest image lacks which required image element?

Anatomical markers. (All radiographic images must contain anatomical markers. Patient shielding, while important, is not a required element on chest images. Images are not required to contain radiographer initials or exposure factors.)

In cassette-based computed radiography (CR) systems, the photostimulable phosphor plate is made of which material?

Barium fluorohalide. (Barium fluorohalide is commonly used as the phosphor in CR imaging plates. Cesium iodide is used as the phosphor layer for indirect capture digital radiography (DR) systems. Amorphous silicon is used in direct capture DR systems. Calcium tungstate was used in conventional radiographic screens before the development of rare earth screens.)

At which location is the ionization chamber located in an automatic exposure control (AEC) device?

Between the grid and the image receptor (IR). (For automatic exposure control, the ionization chamber is placed between the gird and the IR so the x-rays can interact with the chamber, which creates an electrical charge. This charge becomes a signal to terminate the exposure. The other locations aren't appropriate ionization chamber locations.)

Which effect will a low signal-to-noise ratio (SNR) have on the appearance of a digital radiographic image?

Decreased contrast resolution. (SNR is largely dependent on the number of photons available for image formation. Fewer available photons results in a low SNR, which in turn results in higher image noise and decreased contrast resolution. Dynamic range refers to the ability of an imaging system to display a range of intensities; the wide dynamic range inherent in digital systems yields superior contrast resolution to that of conventional film-screen systems. Brightness levels are determined automatically, based on a preselected histogram. Spatial resolution is dependent upon detector element size and spacing.)

All other factors remaining the same, how will increasing the source to image receptor distance (SID) from 40 inches to 60 inches affect the appearance of a radiographic image?

Decreased magnification. (Use of a long SID decreases image magnification due to the more divergent photons at the periphery of the beam falling outside of the anatomy of interest. Use of a short SID increases penumbra, which decreases sharpness of detail. All other factors remaining unchanged, reducing the SID increases radiographic density. Although SID affects size distortion (magnification), it has no effect on shape distortion.)

How does a wide window width affect an image?

Decreases contrast. (A wide window width decreases contrast. A narrow window width increases contrast. Brightness is affected by changing the window level.)

How are automatic exposure control (AEC) devices for mammography different than those used with diagnostic radiography?

Greater accuracy is required. (AEC devices for mammography differ from those used in diagnostic radiography in that greater accuracy is required. AEC devices in mammography must be capable of maintaining optical density (OD) within +/- 0.15; AEC in diagnostic radiography must hold OD to +/- 0.20. AEC devices in mammography often provide more cells, not fewer, to image varying densities of breast tissue. Detector location can be moved to image nipple and chest wall breast locations with greater accuracy. Exposures are terminated directly by the AEC just as they are in routine diagnostic exams.)

Opening the collimators wider than necessary using digital radiography has which effect on image quality?

Image noise is increased. -(Increasing the size of the collimated field increases the quantity of scatter produced but does not affect the size of the pixels. Pixel size in digital radiography is determined by the CR scanning frequency or the DR DEL size.)

Which effect does switching to the small focal spot size have on the manifest image?

Image unsharpness decreases. (Using the small focal spot reduces the area of unsharpness on the radiographic image. Focal spot size has no effect on the photographic properties of contrast and density. Size distortion is determined by object image receptor distance (OID) and source image receptor distance (SID).)

Which is the best way to avoid excessive quantum noise when using cassette-based digital systems?

Increase the amount of exposure to the image receptor. (Quantum noise results when an insufficient number of photons is available for image formation, so increasing the exposure to the image receptor will decrease image noise. Operating at a higher speed class increases the potential for quantum noise due to the lower exposures required. The window level may be adjusted to increase or decrease image brightness, but an image with substantial quantum noise will continue to exhibit poor contrast resolution. Incomplete erasure of plates may result in image artifacts due to residual exposure, but this does not contribute to quantum noise.)

Which technical factor increases the number of x-ray photons reaching the image receptor (IR)?

Increased milliamperage (mA). (An increase in mA increases the number of x-ray photons reaching the IR.)

Which image, when performed according to normal standards, will demonstrate the greatest magnification of the anatomy of interest?

Lateral cervical spine. (Because lateral cervical spine xrays typically have large object-to-image-receptor (OID) distances, the cervical spine anatomy is magnified. The OID for an AP lumbar spine may be minimized by asking the patient to bend his or her knees to bring the spine closer to the image receptor (IR). PA hands and lateral forearms have minimal magnification.)

Which is the primary advantage of a rotating anode?

Less heat is generated at the target. (The primary advantage of a rotating anode is that less heat is generated at the x-ray tube target. More heat is generated with a fixed anode. A rotating anode does not increase or decrease filament temperatures.)

When using digital imaging, which has the greatest influence on contrast?

Lookup table (LUT). (In digital imaging, a LUT (C) assigns predetermined grayscale values. KVp (A) controls contrast in film-screen imaging. MAs (B) does not affect contrast. MTF (D) is related to spatial resolution. Johnston and Fauber, Essentials of Radiographic Physics and Imaging, Ch. 12, "Using digital receptors," p. 164. Carter and Veale, Digital Radiography and PACS, 2nd ed., Ch. 3, "Look-up table," p. 42.)

How does aliasing appear radiographically when using computed radiography (CR)?

Two superimposed images, slightly out of alignment. (Aliasing results in two superimposed images, slightly out of alignment. A white line across the image may be dirt in the IR or dust in the reader. Black lines branching across an image may be due to static. Excessive noise has a number of causes, including using small milliampere-seconds (mAs).)

Which factor will have the greatest impact on decreasing recorded detail or spatial resolution?

motion (Motion will cause the greatest decline in spatial resolution or recorded detail. Larger focal spot sizes decrease recorded detail, but not to the extent that motion does. Smaller SIDs and larger OIDS cause degraded recorded detail as well.)