DHA Radiology / Radiographer common mistakes
DHA Radiology / Radiographer · Understand the traps and how to avoid them.
When asked how to increase subject contrast, the candidate changes mAs instead of kVp, or justifies the choice by saying 'more exposure means more contrast.'
Exposure-factor relationships are memorized as isolated facts rather than as differential-absorption principles; digital post-processing also hides density changes, so the candidate never sees the error in clinical practice.
What to do instead
For every exposure-factor question, write the physical effect first: kVp changes beam penetrability and subject contrast; mAs changes photon quantity and receptor signal. Use the 15% kVp rule and practise factor-isolation drills that require stating which factor changes, in which direction, and why.
Applies the inverse square law or grid conversion factor in the wrong direction, such as increasing mAs when moving the tube closer to the patient, or forgetting distance compensation after changing from a 72-inch to a 40-inch SID.
The candidate recalls the formula but does not identify initial and final distances or sanity-check whether the receptor signal should rise or fall; unit cancellation is skipped under time pressure.
What to do instead
Use a three-step template: list knowns with units, compute the squared distance ratio, then ask whether the image would otherwise be too dark or too light. Sanity-check the direction before selecting an answer, and practise combined distance-plus-grid problems.
Labels a radiation effect as stochastic when it has a known threshold, or claims that a single diagnostic exposure can cause a deterministic effect such as erythema or cataract.
The candidate memorizes effect lists without linking them to dose-response mechanisms, threshold dose, latency, and tissue type; deterministic and stochastic categories blur under exam wording.
What to do instead
Build a comparison table with columns for effect, threshold or no threshold, approximate dose range, latency, and tissue affected. For each practice question, state the mechanism before choosing the category, and distinguish tissue reactions from cancer and hereditary effects.
Positions a patient by matching the appearance of a previous image rather than by palpating landmarks, aligning the central ray to the correct point, and placing a marker; obliques are rotated to the wrong degree or the wrong side.
Pattern-matching replaces landmark reasoning, and time pressure encourages shortcuts. The candidate also omits side markers or accepts a repeat image without diagnosing the centering error.
What to do instead
Use a pre-exposure checklist for every projection: patient identity, side marker, landmark, central ray, receptor alignment, and rotation degree. Verbalize the landmark before positioning, and review rejected images by asking which landmark or alignment check failed.
Confuses spatial resolution with contrast resolution, or describes noise as blur; when asked which metric measures detector efficiency, the candidate selects MTF instead of DQE.
The terms overlap in casual clinical language, and the candidate has memorized definitions without units, measurement methods, or the physical quantity each metric describes.
What to do instead
Define each metric with its unit and a measurement example: line pairs per millimetre for spatial resolution, grey-level discrimination for contrast resolution, MTF for transfer of spatial frequencies, and DQE for signal-to-noise performance. Compare paired metrics in a table and explain one clinical consequence of each.
Recites quality-assurance test frequencies and tolerances without linking them to the equipment failure they detect, so the candidate mixes up daily, weekly, monthly, and annual tests or accepts an out-of-tolerance result.
The schedule is learned as a list rather than as a risk-control programme; the candidate does not connect each test to the patient-safety consequence of drift or failure.
What to do instead
For each QA test, write the failure mode it detects, the patient risk if it drifts, the action threshold, and the corrective action. Group tests by daily, periodic, and annual purpose, and practise interpreting a failed result rather than only recalling the frequency.
Misidentifies right and left on axial cross-sectional images, confuses an axial level with a nearby level, or names a structure without using visible body landmarks to justify the level.
The candidate has weak three-dimensional-to-two-dimensional translation and studies labelled images rather than tracing structures across contiguous slices; orientation conventions are not practised.
What to do instead
Trace each structure through a stack of slices from a known landmark, such as the carina or aortic bifurcation. State the side convention aloud for every axial image, draw the orientation, and practise naming structures only after identifying the level from at least two landmarks.
Treats all contrast reactions as anaphylaxis, gives epinephrine for a vasovagal response, or fails to check renal function and prior reaction history before contrast administration.
Emergency protocols are memorized as a single sequence, and risk stratification is skipped; the candidate does not distinguish allergy-like, vasovagal, and chemotoxic reactions or recall modifiable risk factors.
What to do instead
Use a decision tree that separates mild allergy-like symptoms, vasovagal collapse, and moderate-to-severe anaphylaxis, with the correct first action for each. Before every contrast scenario, list contraindications, renal-function checks, prior-reaction history, and extravasation management.
Performs hand hygiene after rather than before patient contact, or doffs personal protective equipment in the wrong order, such as removing gloves before the gown or touching the front of the mask.
The sequence is learned as rote steps without understanding contamination pathways; the candidate cannot explain which surface is clean and which is contaminated.
What to do instead
Practise donning and doffing with a checklist while narrating clean-to-dirty zones. Apply the World Health Organization hand-hygiene moments to simulated patient contacts, and identify the contamination risk at each step rather than memorizing order alone.
Answers ethics and health-law questions by stating a general principle such as 'confidentiality must be maintained' without applying it to the scenario, or fails to recognize when consent, capacity, scope of practice, or mandatory reporting is the decisive issue.
The candidate studies principles in isolation and does not rehearse fact patterns; legal concepts such as assault, battery, negligence, and informed consent are not distinguished in context.
What to do instead
Work through short case scenarios and identify the legal issue, the applicable rule, the exception, and the correct action. Build comparison notes for consent, capacity, confidentiality exceptions, scope of practice, and reporting duties, and justify each answer with the specific rule.