How to Guess Better in Radiology Physics Exams

Added: 2026-05-15

[00:00:00]Hello and welcome to another exam tips video. Today we're going to be looking at the art of the educated guess. And I really believe this is an art and a skill that you can develop over time with practice. And it's my hope that learn radiology physics.com will help you to develop this skill. Take two students who know the exact same amount heading into an exam. they can leave that exam with vastly different results based purely on the fact that one student is able to recognize common exam patterns and avoid common exam mistakes because they recognize those patterns.

[00:00:31]You would have seen from the previous video, the shockingly simple math behind passing the FRCR physics exam, that how much you actually know in your exam result can differ greatly. And that's largely due to the fact that we are going to guess many questions in the exam. And in a true false exam like the FRCR exam, we can assume that we're going to get 50% of those right and 50% of those wrong. What happens then if we can skew that ratio from 50/50 to say 7030 or 80/20? Hopefully, you can appreciate what a difference that's going to have on your exam result. And that's what we're going to try and do today. And I'm going to do this by highlighting five common exam patterns that you could recognize. And I say could recognize instead of should recognize because you're not always going to recognize these patterns with every question. But you're going to come across some questions that you don't know the answer to. And you might want to take an extra moment to see if you can recognize one of these patterns. But it's also a reminder, and as humans, we're very good at recognizing patterns really quickly and answering quickly without truly reading the question. It's also a reminder to read the question.

[00:01:33]And you'll see as we go through some of these examples why that's important.

[00:01:37]Now, the first exam archetype or question type we're going to look at is what's known as the wolf in sheep's clothing. Take this question. Indirect detectors typically use a scintillator layer such as cesium iodide to convert electrons into light. Now you can see if you read this very quickly it can be tempting to answer true here. And what we have is what I call a sheep a correct statement. Indirect detectors do use scintillator layers instead of direct detectors which don't have that conversion into light step. So that's a true statement to start off. So already we're thinking true coming into this question. And then they say to convert into light. Well cintillator layers do create light. The wolf is lying within the sheep here though. They don't convert electrons into light. They convert X-rays into light. Very subtle difference here. It looks like an obvious answer with an obvious question, but because we need to examine each part of this question, the three separate parts of this question, we can see that there's a wolf lying in sheep's clothing. The second exam pattern we're going to look at is what I call the red herring. And I'm going to give two examples here. This is the first example. Let's read the question.

[00:02:40]Compton scatter is more likely at higher KVP because higher energy photons are more likely to interact with loosely bound outer electron shells. What happens here is we see Compton scatter and we associate Compton scatter with being more likely than photoelectric effect at higher KVPs and we we know that high energy photons involved with higher KVPs and we know that Compton scatter happens with with interactions with loosely bound out shell electrons.

[00:03:06]There's all these red herrings that are your brain is immediately saying yes.

[00:03:10]Compton SC yes. Yes. You you if you don't examine each part of the question.

[00:03:14]It's going to feel like everything is true in this statement.

[00:03:18]Whenever there's the word because we need to take a step back and say is it truly because of this? Is X truly because of Y? And we know that higher energy photons aren't more likely to interact with loosely outer shell electrons. The higher the KVP or the higher the energy of those photons, the less likely interactions are going to be occur to to occur. So Compton scatter is more likely at higher KVPs than the photoelectric effect. But Compton scatter interactions actually decrease over time with higher KVPs because the uh interaction with loosely bound electrons actually drops off slowly with higher KVPs. There's all these red herrings and we need to really examine the question here. Let's do a slightly different example but still a red herring. Changing the phase encoding direction is a primary method for reducing chemical shift artifact. The red herring here is that it's taken a common artifact reduction method changing the phase encoding direction but it's linked it to an artifact that it doesn't affect. So again it's a reminder to say does X cause Y? Just because X is a way to reduce artifacts does it actually match up with this artifact? And we know that changing the phase encoding direction is a primary method to reduce wraparound artifact or aliasing artifact. And it can also reduce motion artifact. But we know that chemical shift artifact happens in the frequency encoding direction. So we can do things like increase the receiver bandwidth. We can do fat saturation sequences. What else can we do? We can we can reduce the Tesla. That's going to reduce the main magnetic field. is going to reduce the absolute difference between spins in water and spins in fat.

[00:04:55]The next question pattern that we're going to look at is what's called the halftruth. Let's read the question.

[00:04:59]Using an air gap helps reduce scatter and patient dose. Now, what these questions often do is they have one technique like an air gap linked to two outcomes. And often one of those outcomes is right and one is wrong.

[00:05:12]There's a half truth, half is true, half is false. Using an air gap does help reduce scatter, but it doesn't reduce patient dose. Using an air gap means we're going to move the patient further away from the detector. So less scatter is going to hit that detector because of the geometry, but we're going to reduce the intensity reaching the detector. And often in practice, we need to increase the filament current, increase the MAS to get adequate detector exposure, and that's going to increase patient dose.

[00:05:40]And what's useful with a type of question like this is whenever you're faced with a technique, so using an air gap or raising KBP or increasing pitch or some form of technique, look at that technique and then compare it to each one of the outcomes that it's talking about. Air gap does reduce scatter. Does air gap inherently reduce patient dose?

[00:05:59]No, it doesn't. In fact, it may increase patient dose. Then we can look at perhaps the easiest question type. And this is something that you're going to recognize commonly. And if you don't know the answer, this is one of the most surefire ways of actually getting it right and really shifting your ability to make an educated guess. And I call it the fence sitting wet fish. So this is question four in our series here. In nuclear medicine, breastfeeding may need to be paused or stopped depending on the radioaceutical. The key here is the word may. If you see may or potentially or sometimes one of those fencitting uh words within the question, it's often because the examiner knows that there are certain circumstances where this may be true. And when you see these words, often the answer to these questions is true. Now, they can be false. So, if you know the answer to the question and it's false, choose false. If you don't know the answer at all and you've got these wishy-washy fencitting wording like may or potentially or sometimes, then go for the answer being true because a likelihood is that the examiner is thinking about a specific scenario and needs to use this wording for that scenario to be true. And the last archetype that we're going to be looking at today is the blink and you'll miss it. My least favorite type of question, but it comes up in exams so often. I think these questions should be illegal, but they they do come up and so we need to u be aware of them. So let's look at the question here. An intravvicicular injection is the most common route for radioarmaceutical administration. You can see why you could read this quickly and think yes we always give radioacearmaceuticals we pretty much always give them intravascular or introvenously. The question here is intravvicicular radioacearmaceutical given directly into the bladder which is very rarely done.

[00:07:40]Now, I don't like this question type, but often I've seen a subtle wording change like this. And you'll be surprised at how many people just get this wrong. Actually, this question or all of these questions are from learn radiology physics.com. And the number of people that have gotten this specific question wrong, that's why I've chosen it and that's why I've included it in the questions is astounding. And I know that people know that you don't give radios into the bladder. But this subtle wording, blink and you'll miss it, and it's very easy to make that mistake.

[00:08:07]Now, with all of these questions, I've included these archetypes throughout the 2,00 questions in learn radiology physics.com. In fact, I've identified 13 so far typical exam question or patterns that come up. So, in another video, I'm going to cover the rest of those. These are common ones that do occur commonly in exams. So, hopefully you'll have a better idea when you don't understand a question or you're not sure what the answer is. Hopefully, these can guide you to make a better or more educated guess and ultimately improve your exam result. So, I'll see you all in another one of these tips videos. Until then, goodbye everybody.