Procedures · ARRT Radiography
Pathology
Additive and destructive pathology for the ARRT exam: why ascites takes more exposure and emphysema takes less, the osteopetrosis vs osteoporosis mix-up, and when AEC does it for you.
Overview
Two words decide which way your exposure moves. 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. For a condition you have not met before, reason out 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 that carry an exposure column, and reports them honestly: most rows read None, and several 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 every other row presents as gas, free in the peritoneum or in air-filled bowel.
The exceptions are the rows worth learning. 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 takes a significant decrease. Osteogenesis imperfecta carries the only number in the 17 tables, 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 image brightness, is what reveals the error.
What you’ll learn in this chapter
The 17 study slides and 12 quiz questions in this chapter break down as follows. 3 chapters are free in full with a free account. The others come with a paid plan, and paid plans open soon.
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 Common Conditions
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 8 key terms 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 easy to mix up 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 + or + + 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 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, not image brightness, shows overexposure.
Sample practice question: Image Acquisition
One free sample question from the Image Acquisition subcategory, like those in its 367-question bank. Several chapters share each sample, so it may not match this chapter's topic. See the format, the rationale style, and the difficulty before you sign up.
An exposure is made at 80 kVp and 4 mAs at 72 inches SID. To keep receptor exposure constant at 40 inches SID, what new mAs is required?
Show answer and rationale
A, Incorrect: 1 mAs is about 19% less than the formula requires. Apply the square law.
B, Incorrect: Distance is decreasing, so mAs should decrease, and by more than half. 2 mAs is still too high.
C, Correct: Correct. Square law: 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. This is the formula reversed: a shorter distance requires less mAs, not more.
Read 3 chapters free.
The free tier unlocks 3 complete chapters, 50 practice questions, and 1 sample timed exam. No credit card required.
Frequently asked questions
What does the Pathology chapter cover?
Two words decide which way your exposure moves. 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. For a condition you have not met before, reason out the direction: name the baseline tissue, name what replaced it, then ask whether the replacement is denser.
How many study slides are in the Pathology chapter?
This chapter has 17 study slides and 12 quiz questions across 14 sections. The full chapter comes with a paid plan, and paid plans open soon. The free tier includes 3 complete chapters.
Is this chapter aligned with the current ARRT Content Specifications?
Every chapter on this site is mapped to the ARRT Radiography Content Specifications, but our line-by-line check against ARRT's outline isn't finished, so keep ARRT's outline beside it. Nothing here follows your exam date, so check which version applies to you. This chapter falls under the Procedures domain of the official ARRT exam blueprint.