Study guide
11.6 Scan Analysis: Region Placement, Window Level, and Reported Values
ARRT Bone Densitometry Exam
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1 Chapter 1: Exam Orientation & the ARRT Blueprint
1.1 About the ARRT Bone Densitometry Examination 1.2 Eligibility, Structured Education, and Clinical Experience
2 Chapter 2: Osteoporosis, Bone Biology & Risk Factors
2.1 Osteoporosis: Definitions, Types, and WHO Diagnostic Criteria 2.2 Bone Functions, Structural Anatomy, and Bone Types 2.3 Bone Cells, the Remodeling Cycle, and Calcium Homeostasis 2.4 Risk Factors, Secondary Causes, and Bone-Compromising Medications
3 Chapter 3: Indications, Prevention & Treatment
3.1 The Bone Mass Measurement Act: Covered Indications and Coding 3.2 Prevention: Nutrition, Exercise, Smoking Cessation, and Fall Prevention 3.3 Osteoporosis Drug Therapy: Antiresorptive, Anabolic, and Hormonal Agents
4 Chapter 4: Patient Preparation, Support & Radiation Safety
4.1 Patient Support, Disabilities, Ergonomics, and Transfer Techniques 4.2 Patient Instructions: Explaining the Exam, Dose, Duration, and Motion Control 4.3 Patient History, Contraindications, and Pregnancy Screening 4.4 Scan Preparation: Patient Data Entry, Artifact Removal, and Infection Control 4.5 Radiation Safety in DXA: ALARA, Distance, and Dose Levels
5 Chapter 5: DXA Physics & Instrumentation
5.1 Physical Principles of Dual-Energy X-ray Absorptiometry 5.2 Beam Geometries: Pencil Beam and Fan Beam Systems 5.3 Fan-Beam Geometry: Source–Object–Detector Distances, Magnification, and Centering 5.4 The Scan Analysis Algorithm: Soft Tissue, Bone Edge Detection, BMC, Area, and BMD
6 Chapter 6: Measuring & Reporting Bone Mineral Density
6.1 Statistics for Densitometry: Mean, Standard Deviation, and Coefficient of Variation 6.2 T-Scores, Z-Scores, and Reference Database Selection 6.3 Clinical Indications for BMD Testing and the FRAX Tool 6.4 Vertebral Fracture Assessment and Trabecular Bone Score 6.5 Whole Body DXA, Body Composition, and Pediatric Scanning
7 Chapter 7: Quality Control, Precision & Equipment Management
7.1 Accuracy, Precision, and the Sources of Precision Error 7.2 Daily Quality Control, Phantoms, and Control Charts 7.3 In Vivo Precision Studies and RMS-SD Calculation 7.4 Determining and Applying the Least Significant Change 7.5 Maintenance, Repair, Relocation, Cross-Calibration, and Software Upgrades
8 Chapter 8: DXA Informatics & Data Management
8.1 DXA Informatics, DICOM, PACS, and Data Management
9 Chapter 9: Lumbar Spine DXA
9.1 Lumbar Spine Anatomy, Landmarks, and Regions of Interest 9.2 Lumbar Spine Scan Acquisition and ROI Edge Placement 9.3 Lumbar Spine: Compensating for Body Habitus, Variant Anatomy, Pathology, and Low Bone Density 9.4 Lumbar Spine Positioning: The Leg Block, Centering, and Common Challenges 9.5 Lumbar Spine Problems: Poor Bone Edge Detection and Obscured Intervertebral Spaces 9.6 Lumbar Spine: Variant Anatomy, Fractures, Degenerative Pathology, Calcification, and Surgery 9.7 Lumbar Spine Analysis: Vertebral Exclusion and Reporting Rules 9.8 Lumbar Spine Follow-Up Scans and Rate of Change
10 Chapter 10: Proximal Femur DXA
10.1 Proximal Femur Anatomy, Landmarks, and Regions of Interest 10.2 Femur Selection: Right, Left, and Dual Femur Scanning 10.3 Proximal Femur Scan Parameters and Compensation 10.4 Proximal Femur Positioning: Neck Rotation, Shaft Placement, and Positioning Aids 10.5 Proximal Femur Problems: Ischium, Short Neck, Arthritis, Fracture, and Hardware 10.6 Femoral ROI Analysis: Femoral Neck, Total Hip, and Ward's Area 10.7 Proximal Femur Follow-Up Scans and Rate of Change
11 Chapter 11: Forearm DXA
11.1 Forearm Anatomy, Landmarks, and Adjacent Structures 11.2 Forearm Indications and Side Selection 11.3 Forearm Length Measurement, Scan Parameters, and Positioning 11.4 Forearm Regions of Interest: One-Third, Mid, Ultradistal, and Total 11.5 Forearm Problems: Edge Detection, Artifacts, Low Bone Density, and Joint Disease 11.6 Scan Analysis: Region Placement, Window Level, and Reported Values 11.7 Forearm Follow-Up Scans and Rate of Change
12 Chapter 12: Cross-Site Artifacts & Clinical Integration
12.1 Recognition, Impact, and Management of DXA Artifacts 12.2 Clinical Interpretation, Serial Comparison, and Reporting
11.6 Scan Analysis: Region Placement, Window Level, and Reported Values
Key Takeaways Explain This Topic AI
Window level and window width adjust only the displayed brightness and contrast of a DXA image; they do not change bone mineral content, area, or BMD.
Adjusting window level reveals artifacts, bone margins, and region boundaries that are invisible at default display settings, which is why it is an analysis tool at all three sites.
Reported values at every site include BMC in grams, area in square centimeters, BMD in grams per square centimeter, T-score, Z-score, and percent of reference mean.
Graphical displays plot the patient against reference curves and plot serial values over time, and they are interpretive aids rather than the basis for classification.
Every manual region adjustment or bone-map edit must be documented so the identical analysis can be reproduced at follow-up.
Last updated: September 2026
11.6 Scan Analysis: Region Placement, Window Level, and Reported Values
Quick Answer: Analysis is the same discipline at spine, femur, and forearm: verify the bone map against the anatomy, verify region placement , adjust window level to inspect what the default display hides, sanity-check the reported values , and document every manual change . Window level changes only how the image is displayed — it never changes BMC, area, or BMD. The ARRT specifications effective January 1, 2027 add window level to scan analysis at all three sites.
- Window Level and Window Width
- What They Are
A DXA acquisition stores a range of attenuation values far wider than a monitor can display at once. Window width sets how much of that range is mapped to the available shades of grey; window level sets where the centre of that range sits.
Narrow window width = high contrast. Small density differences become visible, but values outside the window saturate to pure black or pure white.
Wide window width = low contrast. More of the range is visible at once, with less differentiation between similar densities.
Raising window level generally darkens the image; lowering it generally brightens it.
The Critical Point
Windowing is a display operation. It changes nothing about the stored data, the bone map, the computed BMC, the projected area, or the BMD. A technologist who windows an image to look at an artifact has not altered the measurement in any way.
This is worth stating plainly because the opposite belief leads to two errors: refusing to window at all, and believing that windowing can "fix" a bad result.
Why It Is an Analysis Tool
The default display is optimized for a typical patient. Outside that typical range, information hides.
Task Windowing approach
Find a faint intervertebral disc space in a degenerative spine Narrow the window to raise contrast at the bone-disc boundary
See the cortical margin in a severely osteoporotic bone Brighten and narrow to bring low-density bone out of the dark end
- Identify overlying aortic calcification Adjust to separate vascular calcification from vertebral bone
- Check whether the ischium underlies the femoral neck Window to distinguish the two overlapping bone densities
- Look for a non-removable artifact Widen first to survey the whole field, then narrow onto the suspicious area
- Examine soft tissue for asymmetry or a retained object Window toward the soft tissue range
- Verify a vertebral compression deformity Adjust to make endplates and vertebral heights clearly visible
- Check the distal reference and carpal boundary on a forearm Narrow onto the distal end
Practically: survey the whole field at a wide window, then narrow onto anything that looks wrong. If the image at default settings looks unremarkable but the number is implausible, windowing is the next step, not the last one.
What Windowing Cannot Do
It cannot rescue a motion-corrupted acquisition.
It cannot correct a mispositioned patient.
It cannot remove a non-removable artifact from the measurement.
It cannot change a region-of-interest placement — that is a separate editing operation.
It does not change anything reported to the clinician.
Windowing lets you see the problem. Fixing it requires repositioning, re-acquiring, editing the region, or excluding the site.
Region of Interest Placement
Region placement is the analysis step that does change the numbers.
Site Placement essentials
Lumbar spine Intervertebral markers in the disc spaces; correct levels labeled from T12 ribs and the iliac crest; global ROI boundaries per manufacturer convention; excluded vertebrae excluded
Proximal femur Neck box at the narrowest part of the neck, perpendicular to the neck axis, clear of ischium and greater trochanter; global ROI boundaries; correct side
Forearm Distal reference correctly identified at the end of the radius and ulna; percentage regions located from the entered forearm length; regions clear of the carpus; radius and ulna resolved separately
Three rules apply everywhere:
Compare the placement against the anatomy , not against what looks tidy.
Adjust manually when automatic placement is wrong , using the manufacturer's tools.
Document the adjustment and reproduce it at follow-up, using the baseline analysis as reference for routine clinical comparison.
Reported Values
Every site reports the same core set:
- Value Unit Meaning
- BMC grams Total mineral within the region
- Area cm² Projected area of the region
- BMD g/cm² BMC ÷ area; the measured quantity
- T-score SD Deviation from the young-adult reference mean
- Z-score SD Deviation from the age-matched reference mean
- % young adult % BMD as a percentage of the young-adult mean
- % age-matched % BMD as a percentage of the age-matched mean
- Plausibility Checks
Spine: do per-level values rise gradually from L1 to L4? A level far above its neighbors contains something dense.
Femur: is the femoral neck value lower than the total hip, as it usually is? Is Ward's area lowest, as it always is — and is it correctly excluded from classification?
Forearm: is the 33% radius higher than the ultradistal, as cortical composition predicts?
All sites: does the BMD equal BMC divided by area? Does the T-score correspond to the BMD given the displayed reference mean?
Serial: is the change plausible for the interval and the therapy, and does it exceed the LSC?
Graphical Displays
Most reports include two graphs:
A reference curve plot , showing the patient's BMD against age-related reference curves with T-score or percentile bands. It communicates position at a glance.
A serial trend plot , showing BMD at successive visits.
Both are interpretive aids . Classification comes from the T-score at a valid site, and significance of serial change comes from comparing absolute BMD difference against the LSC — never from whether a trend line looks like it is going up.
Be alert to a serial plot that silently mixes scanners, sides, or analyses with different exclusions. The graph will happily draw a line through incomparable points.
Documentation
For every analysis, record: regions used and any excluded; manual bone-map or region edits and why; artifacts present and their location; acquisition mode and any low-density option; positioning deviations; and for the forearm, the side and the entered forearm length. Windowing itself does not require documentation, because it changes nothing — but what you found by windowing usually does.