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London Msk Ultrasound Programme Notes by John Leddy Recording images for Logbook
Taking pictures is not why we scan our patients. When you first start scanning it takes considerable effort to make the structures appear as they should, and there is a tendency among some students to continue to search for the ideal picture long after they have passed this stage. The correct approach is to use the scanner to assess the relevant structure by scanning through it in as many planes as required, and then take whatever pictures are required to illustrate your findings. Where possible the picture should be an appropriate section of a recognisable structure, and should be representative of your findings. Picture Quality
It should almost go without saying that the image quality should be the best you can manage. The region of interest should be as close to the centre of the image as practical, with the gain suitably adjusted, and where appropriate, anisotropy eliminated. Something to look out for is spurious features. Artefact, often deep to the structure being examined may often give the appearance in a still image, that there is some abnormality present. This can produce an unnecessary degree of concern when images are reviewed, and so it is worth just taking in the appearance of the whole image before saving it. Labelling and orientation of ultrasound images
How much or how little labelling you do, is a matter of personal taste. Generally, though it is helpful to label images left or right. Further labelling depends on the purpose, and should of course be clear and concise Much has been made of the issue of orientation. Within standard abdominal and small parts ultrasound, which makes up the bulk of radiological departments workload, standard orientation is used. This corresponds to the view of the clinician, looking towards the patients head from the right side of the couch, so that the left side of the screen represents the right side of the patient in cross section, and the cephalic direction in long or coronal sections. This makes scanning easier as moving the probe is intuitive. The problem comes when the relationship between the operator and patient changes, such as when standing behind a sitting patient to scan their shoulder, or sitting beside the patient with the scanner towards the patients feet to do biofeedback. In these cases, maintaining standard orientation would lead to the probe having to me moved counter intuitively to scan the patient. Though this is possible, it requires considerably more of the operators mental faculties, so leaving less of the accurate evaluation of the tissues. We therefore teach that standard orientation is only used when it corresponds to the intuitive probe alignment. Images need to be appropriately labelled in circumstances where this may cause confusion.
Accuracy
The accuracy of measurements is dependent on a number of factors, and attempts to measure things too accurately can be counter productive. When making a measurement it is important to know what the purpose of the measurement is, and take the appropriate care and consideration with the placement of the cursers and with the subsequent interpretation. Use of the Zoom function, though not normally necessary in real time scanning, is very useful in taking accurate measurements of small structures. Protocols What constitutes an appropriate measurement of a particular structure has in many cases been laid down over the years, which makes it possible to have accepted normal ranges. Examples of this from abdominal medicine are the Abdominal Aorta, which is typically measured AP in cross section from the outer border to outer border, while the common bile duct is measured inner to inner border in long section.
Within Msk ultrasound there are similar conventions, but as this is a smaller less well developed field, these are not yet so well entrenched. If you are aware of a serviceable convention – use it. If you are measuring something and are not aware of a standard approach – make one up! The important point is to know what and how you are measuring something – do you use a specific plane? do you measure from the outside, inside or on the boundary? are you measuring the widest section? or what you feel is a true cross section, or are you measuring relative to the plane of the underlying bone? If you are to compare measurements between limbs, subjects or against known standards, then you must be sure that you are measuring the same thing. Advanced functions We are not looking at these in any detail during this session, but you may wish to use the software on your scanner to acquire areas and volumes using different methods. For some of you, 3 and 4 D may also be available, along with elastography Practice! What is relevant? This is a clinical question. The example below is an Achilles tear with the foot in full plantarflexion. If I were to measure the separation to be just the fluid filled space then conservative management may have been considered. As I felt that the intervening bright structure was likely to be thrombus I reported the separation to be a number of centimetres, indicating the need for surgical treatment.
Reports Whether or not your ultrasound findings are going to be used by others, the utmost caution should be taken with drawing firm conclusion from ultrasound findings, and a demonstrable level of competence should be achieved, before potentially hazardous decisions are based on your findings. Even then caution is essential, and where findings are in anyway ambiguous, appearances should be described, and any attempt at interpretation, should be couched in such a way that the degree of uncertainty is evident. Review For the trainee as well as the practicing clinician, the recording of images and reports is essential to developing ultrasound skills, as it enables adequate followup. Ultrasound is largely pattern recognition, and it is only through comprehensive follow up that flaws in our technique and interpretation can be ironed out, and our knowledge base be developed efficiently. |
