American Registry of Radiologic Technologists Certification (ARRT) Image Production and Evaluation Syllabus

Define target exposure index (EIt) and deviation index (DI), and give the DI formula.

EIt is the ideal/target exposure for a given exam. DI = 10 x log10(EI/EIt). It quantifies how far actual exposure deviates from target.

Interpret deviation index (DI) values 0, +1, +3, -1, -3.

DI 0 = correct exposure. +1 = ~26% overexposed; +3 = ~2x (100%) overexposed. -1 = ~20% underexposed; -3 = ~1/2 (50%) underexposed. Target range generally -0.5 to +0.5; outside +/-3 usually requires action.

What does a DI of +3 specifically indicate about patient exposure?

The receptor received approximately twice (2x) the target exposure — significant overexposure; image should be evaluated and technique reduced to lower patient dose.

What are the components/structure of computed radiography (CR)?

A cassette containing a photostimulable storage phosphor (PSP) imaging plate (commonly barium fluorohalide doped with europium) that is processed in a separate CR reader; it is a cassette-based, indirect, two-step process.

Describe the CR image acquisition and readout process.

X-rays expose the PSP plate, storing a latent image as trapped electrons in phosphor traps. A scanning laser in the reader stimulates the plate, releasing light (photostimulated luminescence) collected by a photomultiplier/photodetector, converted to a digital signal. The plate is then erased with bright light for reuse.

What is direct digital radiography (DR)?

A cassetteless system using a flat-panel detector that captures the x-ray image and converts it directly to a digital signal for near-immediate display, without a separate reader step.

Differentiate direct-conversion DR from indirect-conversion DR detectors.

Direct conversion uses a photoconductor (amorphous selenium, a-Se) to convert x-rays straight to electrical charge — no light step. Indirect conversion uses a scintillator (CsI or Gd2O2S) to convert x-rays to light, then a photodiode array (a-Si TFT) converts light to charge.

Compare CR and DR in terms of workflow, dose efficiency, and detail.

DR offers faster workflow (no plate handling), generally higher detective quantum efficiency (DQE)/dose efficiency, and immediate images. CR is cassette-based, lower DQE, slower (requires reader), but more flexible/portable and lower equipment cost.

What is a histogram in digital image processing?

A graphical representation of the distribution (frequency) of pixel values (exposure/grayscale) across the image, used to identify the range of useful signal (anatomy) versus background and to map data for display.

How are values of interest (VOI) and minimum/maximum signal used in histogram analysis?

The system identifies the histogram's data range, locates S1 (minimum) and S2 (maximum) values of interest representing the anatomy, and maps these to the displayed grayscale (LUT) for proper brightness/contrast.

What is a look-up table (LUT) in digital imaging?

A predetermined reference histogram/curve for each body part used to rescale the acquired pixel values, applying appropriate brightness and contrast so images of the same exam look consistent regardless of exposure.

What is histogram analysis error and a common cause?

Incorrect identification of the data of interest, causing improper brightness/contrast rendering. Common causes: wrong anatomical menu/algorithm selection, improper collimation, multiple exposures on one plate, or unexpected prosthetics/scatter.

Define collimation/beam restriction and its two main benefits.

Restricting the size and shape of the x-ray field to the area of interest. Benefits: reduces patient dose (less tissue irradiated) and improves image quality by reducing scatter radiation (improving contrast).

What is the most common and useful beam-restricting device?

The collimator (variable-aperture, with two sets of adjustable lead shutters and a light-localizing field). It also produces an unsharp border and a light field for centering.

Name three types of beam-restricting devices.

Aperture diaphragm (fixed lead opening), cones/cylinders, and the collimator (adjustable). Collimators are most versatile.

How does collimation affect scatter and contrast?

Increased collimation (smaller field) reduces the volume of tissue irradiated, decreasing scatter production, which increases radiographic contrast and lowers receptor exposure (may require a compensatory mAs increase).

What is the purpose of a radiographic grid?

To absorb scatter radiation that exits the patient before it reaches the image receptor, thereby improving image contrast. Used with thick parts (>10 cm) and high kVp.

Define grid ratio and give its formula.

Grid ratio = height of the lead strips (h) divided by the distance between them (D): GR = h/D. Higher ratios absorb more scatter (more efficient) but require greater positioning accuracy and more exposure.

Define grid frequency.

The number of grid lead strips (lines) per unit length, expressed in lines per inch (lpi) or lines per cm. Higher frequency produces less visible grid lines but requires more lead/exposure for equivalent cleanup.

What is the grid conversion factor (Bucky factor)?

The factor by which mAs must be increased when adding a grid (or changing grids) to maintain receptor exposure. GCF = mAs with grid / mAs without grid; it increases with grid ratio.

Give the grid conversion factor formula for changing mAs between two grids.

mAs1 / mAs2 = GCF1 / GCF2. Solve for the new mAs using the ratio of grid conversion (Bucky) factors.

Differentiate a parallel (linear) grid from a focused grid.

A parallel grid has lead strips perpendicular to the IR (vertical), prone to grid cutoff at the periphery. A focused grid has strips angled to match beam divergence, converging at the focal distance, allowing greater field coverage with less cutoff.

List the four common grid errors (cutoff) for a focused grid.

Off-level (tube or grid angled across strips), off-center/lateral decentering, off-focus (SID outside focal range), and upside-down focused grid. Each produces grid cutoff (decreased exposure).

What is the grid focal range?

The recommended range of SIDs over which a focused grid can be used without significant grid cutoff. Using an SID outside this range causes peripheral cutoff; higher grid ratios have narrower focal ranges.

What is the air gap technique?

An alternative to a grid that increases the OID (typically 6-10 inches) so scattered photons exiting the patient diverge and miss the IR, improving contrast. Drawback: increased magnification; often a compensatory SID increase is used.

What three primary factors affect the amount of scatter radiation produced?

kVp (higher kVp = more forward-scattered, greater % scatter reaching IR), patient/part thickness (thicker = more scatter), and field size/volume of tissue irradiated (larger field = more scatter).

How does increasing kVp affect scatter and image contrast?

Higher kVp increases the proportion of Compton (scatter) interactions and produces more penetrating scatter that reaches the IR, decreasing image contrast (longer grayscale).

Which interaction is responsible for most scatter reaching the image receptor in the diagnostic range?

The Compton (incoherent) scattering interaction. It produces scattered photons that fog the image and degrade contrast; it is also the main source of occupational exposure.

What does PACS stand for and what is its function?

Picture Archiving and Communication System — a networked system for the acquisition, storage, retrieval, distribution, and display of digital medical images and reports.

What is DICOM and what does it standardize?

Digital Imaging and Communications in Medicine — the universal standard for formatting, storing, transmitting, and exchanging medical images and associated data so equipment from different vendors is interoperable. It defines file format and network communication protocols.

What is included in a DICOM file header?

Patient demographics and metadata (name, ID), exam/study information, acquisition parameters (technique, modality), and image attributes — embedded with the pixel data in the DICOM object.

What is the role of the RIS and HL7 relative to PACS/DICOM?

The RIS (Radiology Information System) manages scheduling, patient tracking, and reporting; HL7 (Health Level 7) is the standard for exchanging textual/administrative data (orders, reports) between the RIS/HIS and PACS, while DICOM handles the images.

What luminance and ratio standards apply to diagnostic display monitors?

Diagnostic monitors should have high maximum luminance (typically >=350-450 cd/m2, often ~500) and the calibration should follow the DICOM GSDF. Primary diagnostic monitors are usually 3-5 megapixel grayscale with controlled ambient lighting.

What is the DICOM Grayscale Standard Display Function (GSDF)?

A standardized calibration curve that maps stored pixel values to luminance so that grayscale appears perceptually consistent (equal perceptual steps) across different calibrated display devices.

What test pattern is used to evaluate display monitor quality?

The SMPTE (Society of Motion Picture and Television Engineers) test pattern, used to assess luminance, contrast (0-5% and 95-100% patches must be distinguishable), spatial resolution, distortion, and grayscale.

List common quality control (QC) tests for radiographic equipment.

kVp accuracy, mR/mAs linearity and reproducibility, timer accuracy, half-value layer (beam quality/filtration), focal spot size, beam (light field)/x-ray field alignment, and collimator/central ray alignment.

What is the acceptable tolerance for x-ray beam/light field alignment?

The light field and x-ray field must align within +/-2% of the SID; central ray perpendicularity within ~1 degree (collimator/beam alignment test).

What is the acceptable tolerance for kVp accuracy and exposure reproducibility?

kVp should be accurate within +/-5% (or +/-4-5 kVp); exposure reproducibility should be within +/-5% for repeated identical settings.

What is the half-value layer (HVL) and minimum filtration requirement?

HVL is the thickness of absorber (mm Al) that reduces beam intensity by half — a measure of beam quality/penetration. Total filtration must be at least 2.5 mm Al equivalent for units operating above 70 kVp.

Define a radiographic artifact.

Any unwanted optical density, signal, or feature on an image that does not represent the patient's anatomy and may obscure or mimic pathology.

Name common CR/PSP imaging plate artifacts.

Light fog/incomplete erasure (ghosting from prior image), dust/scratch lines, phantom/ghost images from delayed reading, light leaks, and quantum mottle from underexposure.

What is a Moire (aliasing) artifact in digital imaging and how is it avoided?

A wavy/grid-line interference pattern that occurs when a stationary grid's frequency is similar to the laser scan/sampling frequency, or the grid lines align with the scan direction. Avoided by using grids with appropriate frequency or orienting grid lines perpendicular to the plate scan direction.

What does quantum mottle (noise) look like and what causes it?

A grainy, mottled appearance caused by insufficient photons reaching the receptor (too few quanta) — i.e., underexposure (low mAs). Corrected by increasing mAs to raise receptor exposure.

What is dead pixel/detector drop-out artifact in DR?

Nonfunctioning detector elements producing missing or constant-value pixels; corrected by detector calibration (flat-field/gain calibration) which maps and interpolates defective DELs.

What is repeat/reject analysis and why is it performed?

A QC process tracking the number and causes of repeated/rejected images to identify problems (positioning errors, exposure errors, equipment faults), reduce patient dose, and improve technologist performance and department efficiency.

What is the typical acceptable repeat/reject rate and the most common cause?

A target repeat rate is generally around 4-8% (often cited as <5%). Positioning errors are the most common cause of repeats.

How is repeat (reject) rate calculated?

Repeat rate (%) = (number of repeated/rejected images / total number of images taken) x 100.

What is detective quantum efficiency (DQE) and which systems have higher DQE?

DQE measures how efficiently a detector converts incident x-ray photons into useful image signal (dose efficiency). Higher DQE means less dose needed for equivalent image quality. DR (especially CsI indirect and a-Se direct flat panels) generally has higher DQE than CR.

How does OID influence both spatial resolution and scatter reaching the IR?

Increasing OID worsens spatial resolution and increases magnification, but it also acts as an air gap, allowing scattered photons to diverge away from the IR, which can reduce scatter and improve contrast.

What is exposure latitude in digital radiography, and what is its risk?

The wide range of exposures over which a digital system produces an acceptable-appearing image (much wider than film). The risk is 'dose creep' — technologists overexposing because images still look good, increasing patient dose unnoticed without monitoring the exposure/deviation index.