Art and Science of the Diagnosis of Gallbladder Disease
The Common Vein Copyright 2008
|Art of Diagnosis|
In general, the diagnostic process of imaging requires a variety of skills and tools.
We will first discuss the principles thgat allow us to see structure, and then the skills required and relating to the reader of the images, followed by the tools and function they play, and finally the art of diagnostic imaging
The Skills of the Reader
The skills of the reader of the images, most commonly a radiologist, relate to a process in which many aspects of the patient are reviewed, integrated, and placed in the context of a clinical problem. The interpretation of the images needs to be correlated with the clinical problem, and hopefully provide an accurate diagnosis that is helpful in the management of the patient. The process by which the reader comes to this point include the same basic elements that any other well functioning component of the body goes through in providing a valuable service. The viewer has to receive the information, process it, and then provide (and export) a valuable interpreation. The steps that follow below comply with this simple formula.
Receiving the Information
The reader of images starts out with reviewing the history of the patient, in order to have some clue as to what subsequent findings may have relevance. Each radiologist has a method of looking at images and these skills change as time and experience evolve, and as the technology and different methods of portraying the images evolve. Either way the next level after looking at the images in an individualized and meticulous manner is the first event of the cognitive process – detection.
At the frst level of cogntion, detection is necessary. The reader has to be able to identify that which is abnormal. This aspect is essential and the process cannot move forward unless this event takes place. No matter how smart, or how much book knowledge a person has, without detection of the abnormality the diagnostic process cannot proceed.
Once detected, perception of the abnormality is necessary, which implies that a 3D picture of the image or an innate sense of the abnormality needs recognition. For example a rounded defect on a CTscan that looks like a nodule on one axial image, when viewed with images both above and below may turn out to be a tubular abnormality. The perception of the structure being a nodule is therefore altered and the true perception is one of a tube.
A decision is usually unconciously made at this point as to whether the abnormality is a mere curiosity in which case no more time will be spent on it, or whether it is worth analysing. If the latter is true, its size shape position and character is analysed. Of these the most difficult is characterization of the abnormality and the the tools provided by modern technology provide this facet and allow us to decide whether the detected abnormality is solid or cystic, enhancing or non enhancing, fat, calcific, or air containing, among many others characteristics of the lesion.
After analysing the abnormality, we start to comprehend the information in our cortex, so although we may not have reached a diagnosis, some form of understanding is in place.
Knowledge, memory and experience now come into play as we integrate what we have seen and comprehended with what we have learned and what we know. The penny either drops or it does not. A diagnosis made is not a diagnosis in isolation since by the nature of disease there is a chain reaction to all events. Thus for example if the diagnosis of acute cholecystitis is made by ultrasound, then it behoves the radiologist to look in the pelvis for free fluid to determine if a complication has taken place.
Judgement and Prudence
One step beyond integration is the decision as to whether the findings have relevance to the patient and the current symptoms, whether it is an associated finding, implying it is important but not of immediate relevance, or whether it is an incidental finding in which case it is a mere curiosity. The review of prior studies is essential before we make our final judgement. Finding a spiculated nodule on a chest CT that may have been present for more than two years is entirely different from a new finding.
The impression is what we report as our official interpretation of the study, for which we are valued and therefore for which we get paid.
There are traditional tools which include plain film X-ray, CTscanning, ultrasound, nuclear medicine and angiography. We also include the endoscopic techniques since they are truly imaging techniques. The principles that guide us in any diagnostic procedure are universal. They include the aim of the procedure, indication, contraindication, advantages, disadvantages, method (patient preparation, equipment, technique) potential complications, and results.
The true reflection of structure and function is the goal of imaging.
In imaging we thrust certain forces toward the object to be imaged and the object reacts to the force in specific and characteristic ways reflecting its nature and makeup. Thus if we use X-rays as our force then some of the X-rays we thrust upon the structure to be interrogated are totally reflected, some partially reflected and some pass through without reflection. This interaction allows us to define the elements discussed including size, shape, position, character, connections and relations. If we can repeat the interrogation of the same structure at a different time then we can evaluate how it changes with time and circumstance and hence have a window into how the structure functions. In the case of the heart the relevant changes occur every millisecond, and cycle every second, while in the case of the ovary and the endometrium, the relevant physiological events cycle through a month.
Imaging and structure
As we have outlined in the introduction to the common vein, structure is defined by very consistent and specific elements.
All structures have;
As the science of imaging advances, the ability of the tools to reflect the true nature of the structure becomes truer and truer to reality.
Imaging and function
While structure has been within the realm of traditional radiological imaging, the techniques that have allowed us to image how structure changes with time have given us a window into the functional aspects of the body. Thus echocardiography reflects motion of cardiac muscle and cardiac valves, doppler imaging reflects flow in arteries and veins, perfusion imaging reflects, as implied, perfusion of tissue with contrast agents, and diffusion imaging reflecting Brownian motion.
Nuclear imaging with radioisotopes has been a longstanding technique for functional imaging. For many years it not only enabled us to study contractile abilities of muscle as well as blood flow but also enabled us to identify how certain metabolites were handled by the body. The most recent innovation of this technique called PET scanning reflects for example how sugar is handled by the tissues. Diseases such as inflammation and cancer have heightened metabolic needs and hence heightened need and use of glucose. This metabolic need is reflected in the imaging technique and metabolic activity and hence function is reflected.
Structure and function in biology are packaged in one gift, and the one without the other is impossible. Dividingthese two and studying them separately is the huma way of attempting to understand them.
Medical imaging is indicated when a person is suspected of suffering from a disorder and accurate diagnosis eludes the usual preliminary investigations that include taking a clinical history, examining the patient and running a battery of preliminary blood tests.
Absolute contraindications to imaging are rare. There are a few relative contraindications to certain imaging techniques under specific physiological or clinical situations. For example the use of X-rays during the period of featal organogenesis is relatively contraindicated. There are alternatives in this situation. For example ultrasound would be considered quite safe during this period.
MRI is contraindicated in patients with pacemakes, certain metallic implants, or metallic foreign bodies that have inadvertantly been implanted while working.
Intravenous contrast is relatively contraindicated in patients with severe contrast allergy, or patients with renal failure. Claustrophobia is a real problem for some patients and this is also a relative contraindication. However in general, medical imaging is quite safe with relatively few contraindications.Patients who are allergic to intravenous contrast would
The advantages of medical imaging is to enable more accurate diagnosis of structural and or functional abnormality in order to provide optimal therapy
Medical imaging is stressful, sometimes uncomfortable, costly, and has risks of radiation exposure.
It is imperative for all the studies that the patient is well prepared both physically and psychologically. For a gallbladder using ultrasound, it is imperative that the patient is in the fasting state since ingestion of food causes the gallbladder to contract and limits visiualization and therefore evaluation of the gallbladder.
A nuclear medicine study is a two part examination. There is first the injection of the radioisotope, and then image acquisition. These may be hours or even a day apart. The time the patient has to deote to the study should be well explained. The patient also has to lie quietly for 20-40 minutes during acquisition. The patient has to be able to do this otherwise the study may be unreadable.
The patient has also to be prepared psychologically for the exam and to know what to expect. The MRI study requires that the patient lie still in the gantry, while being subjected to a battery of uncomfortable noisesA patient arricing for a nucleatr medicine study should know how long the study takes and also that they are required to lie still.
Not all equipment is equal. The difference between an 8slice MDCT scanner and a 64MDCT scanner is enormous. Similalrly there are strengths and limitataions based on technology and manufacurer.
Plain film radiography requires accurate positioning of the patient, accurate positioning of the equipment, and appropriate utilization of Kv and mA. Ultrasound evaluation is operator and patient dependent. Operator’s skill and experience varies significantly and hence the results obtained will vary. CT is less operator dependant and overall good studies are usual even when the patient is large. MRI is dependant on protocols provided by the radiologist since there are so many sequences that each bring out different characteristics of the disease process. The patient has to be still in the scanner and any movement will degrade the image significantly.
(1) Component parts.
(2) A size or a dimension.
4) Position in space.
(5) Character, i.e. when a structure interacts with its environment there are characteristic ways in which it will behave. For example, elastic behavior, liquid behavior, hard soft, green blue.
(6) Change with time
7) All biological structures have relationships with other structures, and are connected to other structures and environments. The connections take the form of conduits that bring products in to the structure, conduits that take products out of the structure (arteries, veins, capillaries and lymphatics), or connect to the environment directly in intimate contact.
In general diagnostic imaging has few complications. The application of diagnostic imaging to guided procedures do have inherent procedure related complications but those are not considered complications of the imaging devices but rather of the procedure.
The Art of Diagnosis
Beyond the discussion above is the ill defined art of diagnosis and below we describe the clues and inspirations from the greatest detective of them all –
Holmes,…. Sherlock Holmes
Review of all the volumes of the stories of Arthur Conan Doyle a few prudent and inspirational quotes have been extracted.
“Not invisible but unnoticed Watson.You did not know where to look so you missed all that was important.”
“What was vital was overlaid and hidden by what was irrelevant. Of all the facts which were presented to us we had to pick just those which we deemed to be essential and then piece them together in their order so as to reconstruct this very remarkable chain of events.” ( The Adventure of the Naval Treaty)
“Crime is common – logic is rare. Therefore it is upon the logic rather than upon the crime that you should dwell.” (The Adventure of the Coppper Beaches)
“It is of the highest importance in the art of detection to be able to recognise out of a number of facts which are incidental and which vital, otherwise your energy and attention must be dissipated instead of being concentrated. ” (The Adventure of the Musgrave Ritual)
“We approached the case, you remember with an absolutely blank mind, which is always an advantage. We had formed no theories. We were simply there to observe and to draw inferences from our observations.” (The Adventure of the Cardboard Box)
“Elementary,” said he, “it is one of those instances where the reasoner can produce an effect which seems remarkable to his neighbour, because the latter has missed the one little point which is the basis of the deduction.” (The Adventure of the Crooked Man)
“There is nothing in which deduction is so unneccesary as in religion.” said he. “It can be built up as an exact science by the reasoner. Our highest assurance of the goodness of providence seems to me to rest in the flowers. All other things, our powers, our desires, our food are really necessary for our existance in the first instance. But this rose is an extra. Its smell and its color are an embellishment of life, not a condition of it. It is only goodness which gives extras, and so I say again that we have much to hope from the flowers.” (The Adventure of the Naval Treaty)
“The world is full of obvious things which nobody by any chance ever observes.” (The Hound of the Baskervilles)
“It may be that you are not yourself luminous but you are a conductor of light. Some people without possessing genius have a remarkable power of stimulating it.” (The Hound of the Baskervilles)
“I knew that seclusion and solitude were very necessary for my friend in those hours of intense mental concentration during which he weighed every particle of evidence, constucted alternative theories, balanced one against the other, and made up his mind as to which points were essential and which immaterial.” (The Hound of the Baskervilles)
“It is the scientific use of the imagination, but we have always some material basis on which to start our speculations.” (The Hound of the Baskervilles)
The key elements in the evaluation of an image before supratentorial elements (such as knowledge memory experience judgment and wisdom kick in) is the ability to identify the abnormality or clues to the abnormality. This is done by scanning the patient or the image and based on the size shape position and character of all the component structures these incriminating elements are identified for further analysis. Other aspects of the image such as time, relations to other structures and events, are taken into consideration and then clues outside thepatient or the image under review are used such as clinical history, clinical examination other studies, and particularly previous images of the same part