Untitled Quiz

Final Review - Week 9

• The imaging process consists of 5 phases: acquisition, processing, archiving, display, and analysis.
• X-ray production is the same for all systems, although the phases have unique, system-dependent sequences.

Image Acquisition

• Results of interaction between the x-ray beam and the image receptor (IR).
• Creates a latent, invisible image.

Image Processing

• Images can be processed using hard copy or soft copy.
• Hard copy can be digitized into DICOM-format images.
• Monitor/soft copy can be produced as film/hard copy by a laser or dry imaging system.

Image Archiving

• Storing images for reference (hard copies or electronically).

Image Display

• Critical element in both conventional and digital imaging.
• Monitor resolution is the weakest point.

Image Analysis

• Visibility of detail is a critical factor, along with density/image receptor exposure, controlling factors (mAs, kVp), focal spot, anode heel effect, distance, tissue type, filtration, tissue thickness, beam restriction, contrast, grid construction, ratio, and more. The recorded detail is also subject to influencing factors such as geometry, anatomical part, pathology, motion (voluntary or involuntary), and equipment.

Radiographic Image Quality

• Fidelity with which the anatomical structure being imaged is rendered on the radiograph.
• Aspects of image quality affected include image receptor factors, geometric factors, and subject factors such as contrast, thickness, density, and atomic number; as well as motion.

Image Quality

• Important characteristics of radiographic image quality include spatial resolution, contrast resolution, detail, noise, and artifacts.
• Spatial resolution is the ability to distinguish between two separate objects.
• Spatial resolution improves with reduction of screen blur, motion blur, and geometric blur.
• Contrast resolution is the ability to distinguish structures with similar subject contrast.
• Detail and recorded detail are sometimes used instead of spatial resolution and contrast resolution.
• Visibility of detail refers to the ability to visualize recorded detail.
• Noise is unwanted fluctuation of the optical density.
• An artifact is a structure or appearance not normally present and is due to technical, processing, or positioning errors.

Noise

• Can be inherent in the system (structure mottle) or under radiographer control (quantum mottle).
• Use of high mAs, low kV, and slower IR reduces quantum mottle.
• Resolution is the ability of an image receptor to reproduce images of closely spaced small objects.
• Resolution and noise are related; faster IRs typically have higher noise levels and poorer resolution.

Saturation

• Extreme overexposure to the IR overwhelms the digital detection system, resulting in a flat black area. Saturation is not the same as image fog.
• Manipulation of the image may allow retrieval of details within the black area, which then isn’t considered saturation.
• It takes multiple times normal exposure for saturation to occur depending on the sensitivity of the system.

Principal Factors Affecting Image Quality

• A chart detailing the effect of various factors on different aspects of image quality.

The Image Diagnostic Process

• Includes narrowing the search field, activation of hypotheses, information-seeking, and hypothesis evaluation.
• Density changes often require adjustment of mAs (+/- 30%).
• Contrast changes often require adjustment of kVp (+/- 4%).

Distortion

• Any misrepresentation of an anatomy’s shape or size.
• Size distortion is referred to as magnification.
• Shape distortion occurs from elongation or foreshortening.
• Radiographic distances such as OID have a much higher effect on distortion compared to SID.
• Alignment of the IR, CR, and body part must be proper to prevent distortion.

Quality Assurance/Control

• Quality Assurance (QA) addresses identifying and resolving problems in processes related to patient care and technical aspects(equipment).
• Quality Control (QC) addresses the equipment, and is mainly the radiologic technologist's responsibility.

Purchasing Equipment

• Identification of imaging requirements involve radiologists, medical physicists, and CE education/training for at least 2 personnel. Installation and acceptance testing as well as ongoing monitoring of equipment performance and system evaluation.

Computers in Medicine

• Generations of computer use including vacuum tubes, transistors, silicon chips, and large-scale/very large-scale integration.
• Analog refers to continuously varying quantities, whereas digital uses discrete values.
• Computer hardware consists of physical components.
• Computer software gives instructions for the hardware.
• Computer languages use binary code ("0s" and "1s").
• A binary digit (0 or 1) is called a bit; 8 bits grouped together make a byte.
• Computer words consist of 2 bytes.
• Digital images have pixels (picture elements) arranged in a matrix.

Computed Radiography

• A form of digital radiography using an imaging plate.
• Terminology including IP, photodiode, PMT, PSL, PSP, SP, SPS, and more.
• Uses luminescence/phosphorescence to record x-ray images.
• Includes information about image receptors, latent images from PSP technology, and laser beam diameters/spatial resolution.
• Various noise sources (mechanical, computer, optical and more) affect image quality.
• CR systems are faster than film and need lower mAs.
• kVp controls subject contrast, mAs controls IR exposure.

Digital Imaging

• Film digitizers convert film to digital images.
• Digital imaging (DR) has direct and indirect conversion techniques.
• Direct conversion uses an array of detectors.
• Indirect conversion uses a scintillator to convert radiation into visible light then electronic charge.
• Advantages of digital imaging include wide dynamic range, linear response to exposure, and ease of visualizing different anatomical areas.
• Digital images are recorded as a matrix of pixels.
• Matrix size is rows and columns of pixels and it effects pixel size.
• A higher matrix size will always decrease the pixel size to improve resolution if the FOV is constant.
• Bit depth affects digital image contrast.
• Postprocessing for display includes: annotation; image inversion; window/level adjustments; magnification/zooming; scroll/pan; image flip; image subtraction; pixel shifting.
• Preprocessing for digital images includes electronic calibration and noise reduction.
• Raw images vs. processed images to understand storage implications.
• Various factors affecting image quality.

Digital Imaging - Human Anatomy

• Different anatomical structures have different spatial frequencies.

Digital Imaging - MTF (Modulation Transfer Function)

• MTF describes how well an imaging system can render objects of different sizes.

Digital Imaging - Contrast Resolution

• Dynamic range (the number of shades of gray) is identified by bit depth (e.g., 8-bit = 256 shades, 16-bit = 65,536 shades)

Digital Imaging - Signal-to-Noise Ratio (SNR)

• Measures the ratio of true signal to noise.
• Dose creep describes increasing radiation doses.
• Technique creep describes the method of reducing patient dose by using higher kV and lower mAs settings.

Digital Imaging - Viewing of Digital Images

• Defines and describes the photometric quantities of lumens, illuminance (lux), and luminance (nit).

Digital Imaging - Fundamental laws

• The inverse square law and the cosine law are fundamental photometric laws.

Digital Imaging - Postprocessing

• Designed for optimizing digital image viewing.

Digital Imaging - Preprocessing

• Designed to improve artifacts in digital images by removing or minimizing errors (e.g. calibration, noise reduction).

Processed versus Raw Images

• Processed images enhance visualization and are more useful for clinical interpretation.
• Raw images are necessary in cases where issues or inconsistencies arise during processing.

Digital Imaging - Spatial Frequency

• Frequency is expressed as line pairs per millimeter (lp/mm).
• Higher spatial frequency values equate to higher quality of images and smaller resolution images.