Radiographic Procedures · ARRT 2025
Pathology
Additive and destructive pathology for the ARRT exam: why ascites takes more exposure and emphysema takes less, the osteopetrosis vs osteoporosis trap, and when AEC does it for you.
Overview
Two words decide which way your exposure moves, and the ARRT exam tests both. Additive means something denser has moved into a space, so attenuation rises and the part needs more exposure. Destructive means denser tissue has moved out, replaced by air, fluid, or nothing at all, so it needs less. The exam deliberately hands you unfamiliar conditions because the skill tested is reasoning the direction: name the baseline tissue, name what replaced it, then ask whether the replacement is denser.
The chapter works through the 17 clinical indications tables, one per region, and reports them honestly: most rows read None, and six tables print None in every row. The abdomen table is the exception that always moves. Ascites is its only increase, and the only double plus in the set, while everything else goes down, because acute abdomens present as gas where gas should not be.
The exceptions are where questions live. Osteopetrosis lays down dense marble bone and takes an increase, while osteoporosis takes bone away and takes a decrease, two letters apart with opposite answers. Emphysema is significantly decreased. Osteogenesis imperfecta carries the only number in the whole set, a decrease of up to 50 percent. And two plus rows are not density at all: Lisfranc injury needs penetration through a thick tarsal region, and pituitary adenoma compensates for a tightly collimated field.
Finally, the chapter covers when any of this matters. A correctly calibrated AEC generally removes the need for manual adjustment. Manual, tabletop, and mobile work is where the adjustments are live, and on digital systems the exposure indicator, not the image, is what reveals the error.
What you’ll learn in this chapter
The 29 lessons in this chapter break down as follows. The full lesson content is unlocked when you start a free account.
Pathology
- Additive and Destructive Disease
The system
- Additive Disease
- Destructive Disease
- Quiz
- Reasoning a Condition You Have Never Seen
Exposure consequence
- AEC and the Technique Chart
- Quiz
- What Digital Forgives
Additive or destructive
- Sorting the Ones That Get Examined
Chest
- Chest
- Quiz
Abdomen
- Abdomen
- Quiz
Extremities
- Extremities
Skull
- Skull and Facial Bones
Spine & thorax
- Spine and Bony Thorax
- Quiz
Contrast studies
- Contrast Studies
- Quiz
Consolidated
- Every Adjustment in One Place
Contradictions
- Where the Tables Disagree
- Quiz
Reality check
- The Nones
Recap
- What to Carry Out of This Chapter
- Quiz
- Quiz
- Quiz
- Quiz
- Quiz
Key terms in this chapter
These are the 8 terms most likely to appear on the ARRT registry from this chapter. Use them as a flashcard pre-quiz.
- Additive pathology
- A condition in which something denser than the normal tissue moves into a space, raising attenuation. The region appears radiodense and needs an increase in exposure factors.
- Destructive pathology
- A condition in which denser tissue is replaced by something that attenuates less, often air or lost bone mineral. The region appears radiolucent and needs less exposure.
- Osteopetrosis
- Marble bone: hereditary, abnormally dense bone that can obliterate the marrow space. An additive condition requiring an increased exposure adjustment.
- Osteoporosis
- A reduction in the quantity of bone, showing a thin cortex and scanty trabeculae. A destructive condition requiring a decreased adjustment, and the classic paired distractor with osteopetrosis.
- Ascites
- Fluid in the peritoneal cavity producing general abdominal haziness. The only row in the abdomen table that takes an increase, printed as one or two plus steps depending on severity.
- Emphysema
- Hyperinflation with a barrel chest, flat diaphragm, and radiolucent lungs. The chest table gives it a significantly decreased adjustment, scaled to severity.
- Osteogenesis imperfecta
- Abnormally soft, fragile bone. It carries the only numeric adjustment in all 17 tables: a significant decrease of up to 50 percent, from the pediatric skeletal table.
- Exposure indicator
- A numeric value representing the exposure the receptor received, known by vendor names such as S number, EI, EXI, REX, or DEI. On digital systems it is the only reliable check for overexposure.
Sample practice question: Image Acquisition
One free sample from the 98-question Image Acquisition bank. See the format, the rationale style, and the difficulty before you sign up.
An adult chest x-ray is performed at 80 kVp and 4 mAs at 72 inches SID. To maintain density at 40 inches SID, what new mAs is required?
Show answer and rationale
A, Incorrect: 1 mAs would result in significant underexposure. Apply the density maintenance formula.
B, Incorrect: Distance is decreasing, so mAs should decrease, but not by half.
C, Correct: Correct. Density maintenance formula: mAs₂ = mAs₁ × (SID₂² / SID₁²) = 4 × (40² / 72²) = 4 × (1600/5184) = 4 × 0.309 ≈ 1.2 mAs. Closer distance means more intensity, so less mAs is needed.
D, Incorrect: 13 mAs would more than triple the exposure. Reversed formula error, increasing distance requires more mAs, not less.
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Frequently asked questions
What does the ARRT Radiography Radiographic Procedures category cover?
Two words decide which way your exposure moves, and the ARRT exam tests both. Additive means something denser has moved into a space, so attenuation rises and the part needs more exposure. Destructive means denser tissue has moved out, replaced by air, fluid, or nothing at all, so it needs less. The exam deliberately hands you unfamiliar conditions because the skill tested is reasoning the direction: name the baseline tissue, name what replaced it, then ask whether the replacement is denser.
How many lessons are in the Pathology chapter?
This chapter contains 29 lessons across 14 sections, plus a knowledge-check quiz at the end. The full lesson content is unlocked with a Premium subscription. The free tier includes 3 complete chapters.
Is this chapter aligned with the ARRT 2025 Content Specifications?
Yes. Every chapter on this site maps directly to the ARRT Radiography Content Specifications effective 2025. This chapter falls under the Radiographic Procedures domain of the official ARRT exam blueprint.