The linear and non-linear thinking of diagnostic radiology.
Let’s play a game. Lay your hand down on the table, and write the letter A on your thumb. Then, continue lettering B, C, D, and, lastly, E on your pinkie finger. Now find the quickest path from A to E by connecting the letters. One way to do it is to draw a path from A down one finger to B up the next finger to C to D to E….but you could also pinch thumb and pinkie together to achieve the same goal. The difference in methods is sometimes called linear vs non-linear thinking. Within the frame of linear thought processes, A flows to B before arriving at C, and so on. Once you lay your hand on the table, it becomes a two dimensional surface and linear thinkers tend to connect the letters by drawing a line in sequential order. On the other hand, non-linear thinkers use “spatial jumping” and form connections in a non-sequential way. Neither is right or wrong, nor the superior method; rather, these categories are a way to describe thought processes. In the reading room, diagnostic radiologists often employ linear thinking as a method to logically and sequentially document findings. First, there is the search pattern. As a new radiology resident, I was instructed to figure out my preferred search pattern for each type of exam and to stick with it for each patient. This organizes thought processes and creates a work flow that divides large amounts of data into digestible pieces. Furthermore, having a consistent search pattern reduces the human error of simply forgetting to look. Secondly, we employ the linear thought process of figuring out differential diagnoses. If A, then B. If C, then D. How many times do we use this a day? As a trainee, the learning curve is to memorize imaging characteristics and differential diagnoses so that these connections can be made faster. In fact, study aids like mnemonics only work if they are memorized in a specific order, otherwise they wouldn’t make sense. Perhaps writing “MAGIC DR” on our fingers would have been more helpful at the beginning of this exercise. Anyhow, at the start of training, both visual/motor processes and mental processes use linear thinking to process large amounts of data in an efficient and meaningful way. Over time, the goal is to see so many cases that we know what “normal” looks like. Just as one learns to play a musical instrument or becomes fluid on a bicycle, going through the motions as a radiologist becomes natural (or so I’ve heard). What I mean by this is some motor eye movements become automatic while thought processes become subconscious. I am continuously amazed by veteran radiologists who just “have a feeling” about the image. They can’t quite explain, but they are always right. Once, while reading out with an attending and both staring at the same image, I asked doubtfully, “How do you know that is not artefact?” and he responded, “Just trust me.” It seems that with experience and years of mastering linear thought processes, senior radiologists have somehow developed “trust” and “feelings,” or maybe some kind of sixth sense. They are no longer bound by the constraints of a linear framework. Rather, they seem to make jumps that astound the most astute memorizer (novice). They have entered the realm of non-linear thinking. The prowess to pull together clinical data, process a few thousand cross-sectional images quickly, and to draw a conclusion that truly impacts the patient is a feat which takes years to learn. As an aside, I believe this ability is why computer-aided detection will never replace human interpretation. These non-linear connections are not described in textbooks nor included in rote memorization. They come from experience and compilation of trial and error and seeing thousands of images. I believe these connections are also the reason why we seek to learn from more experienced radiologists, hoping to glean some wisdom. They are also the reason we attend live lectures instead of simply reading about a topic. So, next time you draw letters on your hand, consider that we have opposable thumbs for a reason…which might not be evident until we appreciate all the other fingers first.