Northwestern College
Course Syllabus
DEPARTMENT: SHS - Radiography Program
COURSE CODE: RADS.102
CREDIT HOURS: 3
Course Meeting Date/Times: M/W 8:00 – 9:45 a.m.
TITLE: Radiographic Exposure II
INSTRUCTOR: Gary Gruenewald M.S., R.T(R)
PHONE: 708-237-5000 ext. 2825
EMAIL: ggruenewald@nc.edu
COURSE DESCRIPTION: As a continuation of RADS.101, students further develop their knowledge of x-radiation and how it interacts with matter. The control of primary and secondary radiations using grids, filtration and beam restricting devices is studied. Fixed and variable kilovoltage systems are reviewed. The properties of attenuation and the absorption of radiation and how it is influenced by pathology are also studied. Using information learned in this course, the students continue their analysis of the radiographic image.
Pre-requisite: RADS.101 with grade of C or better or consent of the instructor
REQUIRED TEXTBOOKS:
Carlton and Adler, Principles of Radiographic Imaging, Fourth Edition, Delmar, Albany, New York
Bushong, Radiologic Science for Technologists, Ninth Edition, Mosby, St. Louis, MO
DeAngelis, The Integrated Radiography Workbook, Fourth Edition, Health and Science Publishers, Rutland, VT
COURSE OBJECTIVES: Upon completion of the course, the student will be able to effectively analyze and critique the radiographic image and its variables using the basic principles of medical radiographic exposure and imaging.
Units of Instruction
Unit 1 - The Patient as a Beam Emitter
Unit 2 - Filtration
Unit 3 - Beam Restricting Devices
Unit 4 – Grids
Unit 5 – Fixed/Variable kVp Systems
Course Objectives
Unit 1 - The Patient as a Beam Emitter
On completion of this unit, the student will be able to:
- Explain the process of attenuation
- Describe the basic composition of the human body.
- Describe the effect of the human body on the attenuation of the beam.
- Explain the relationship of the subject to the density, contrast, recorded detail and distortion of the recorded image.
- Describe the effect of pathologic conditions on the attenuation of the radiographic beam.
- Explain the two basic photon-tissue interactions that occur in the diagnostic range.
Unit 2 - Filtration
On completion of this unit, the student will be able to:
- Define filtration, inherent filtration, added filtration, compound filtration, compensating filtration and total filtration.
- Explain the concept of half-value layer equivalency measurements of filtration.
- Appraise various types of filters for specific clinical situations.
- Describe the effect of filtration on the entire x-ray beam.
Unit 3 – Beam Restricting Devices
On completion of this unit, the student will be able to:
- Identify the factors that affect the amount of scatter produced.
- Discuss the primary methods used by radiographers to control the amount of scatter radiation reaching the film.
- Explain the purpose and construction of beam-restricting devices.
- Compare the advantages and disadvantages of the various beam-restricting devices.
- Describe the effect of beam restriction on image quality and patient dose.
Unit 4– Grids
On completion of this unit, the student will be able to:
- Describe the purpose of the grid.
- Explain the construction of a grid, including grid materials, grid ratio, grid frequency and lead content.
- Describe the various grid patterns.
- Differentiate between parallel and focused grids.
- Differentiate between the uses of a stationary and a moving grid.
- Explain the process of grid selection for specific radiographic procedures.
- Explain the relationship of grid selection to patient dose and radiographic density.
- Calculate changes in technical factors to compensate for changes in grid selection.
- Describe methods for evaluating the performance of a grid.
- Discuss common errors that are made when using a grid and the effects of these errors on the radiographic image.
- Describe other scatter reduction methods.
Unit 5 - Fixed/Variable kVp Systems
On completion of this unit, the student will be able to:
- Describe the principles of fixed kVp technique theory.
- Discuss the primary advantages and disadvantages of fixed kVp technique systems.
- Define optimal kilovoltage.
- Explain how to establish fixed kVp for various subject parts.
- Describe the steps in establishing a fixed kVp technique chart.
- Describe a variable kilovoltage technique system.
- Discuss the primary advantages and disadvantages of variable kVp technique systems.
- State the 2 kVp rule.
- Describe the effects on radiographic contrast when using a fixed kilovoltage system compared to a variable kVp system.
Unit I - The Patient As a Beam Emitter
Subject Factors
Radiographic Contrast - The contrast of a radiograph viewed on an illuminator.
Radiographic Contrast = Film Contrast x Subject Contrast
Factors Affecting Subject Contrast
- Patient Thickness
- a thick body part attenuates more x-rays than a thin part
- Tissue Mass Density
- the body may have equal thicknesses but different densities
- Atomic Number
- Compton interactions are independent of the atomic number of the tissue
- Photoelectric interactions are proportional to the cube of the atomic number
- Object Shape
- A structure coinciding with the shape of the beam would demonstrate maximum subject contrast
- Other anatomical shapes present different thickness’ and thus create absorption blur
- Kilovoltage
- the most important influence on subject contrast
- Low KVp = Short Scale Contrast
- High KVp = Long Scale Contrast
A technique that produces low subject contrast (high KVp) allows for a wide latitude in exposure factors.
Subject contrast can be increased by the addition of contrast media.
- Barium (Z = 56)
- Iodine (Z = 53)
Contrast media accentuate subject contrast by increasing photoelectric absorption.
The Pathology Problem
Certain diseases can increase or decrease tissue thickness or alter tissue composition.
- affects the degree of radiation absorption for that tissue.
An understanding of pathology allows the technologist to properly select the correct technical factors for the procedure.
Additive Conditions
If a disease causes the affected body tissue to increase in thickness, effective atomic number and/or density,
there will be a greater attenuation of the x-ray beam.
- requires increasing technique to obtain the proper density
Destructive Conditions
If a disease causes the affected body tissue to decrease in thickness, effective atomic number and/or density,
there will be less attenuation of the x-ray beam.
- requires decreasing the technique to obtain the proper density
A disease influences radiation absorption when it alters the overall number or types of atoms comprising the affected tissue
To produce a visible difference requires a 25% - 50% change in the overall density of the image.
Some diseases do not affect the thickness or opacity of body tissue, but the effects of the disease
can be seen radiographically (i.e. structural or functional changes).
Obtaining and carefully reviewing the patient’s history of symptoms may aid the technologist in adjusting technical factors.
AEC will compensate for most pathological changes, but the adjustment will be in mAs versus kVp.
The technologist may utilize the 15% rule when hypothesizing as to the correct technical factors to use.
For destructive conditions, a decrease of 25% - 50% in mAs will compensate for most pathologic conditions.
Abscess, edema and tumors require an increase in technical factors.