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Journal of Postgraduate Medicine, Vol. 49, No. 3, July-Sept, 2003, pp. 256-262 Education Forum Clinical Photography: A Guide for the Clinician Nayler JR
Department of Medical Illustration, Institute of Child
Health and Great Ormond Street, Hospital for Children NHS Trust, Londona Code Number: jp03070 ABSTRACT Clinicians might not always have available the services of a professional medical photographer, but if a standardised approach is followed those who take their own clinical photographs can achieve acceptable results. This article offers guidance to the clinician on consistent lighting, exposure, patient positioning, linear scale, perspective, depth of field, and background. Advice is given on equipment and materials, including digital and conventional cameras, flash (strobe), films, and processing choices. Consistency of approach is emphasised – it is not acceptable to use photographic tricks to enhance the appearance of clinical outcomes. Rather, care should be taken to ensure that the only changes among clinical photographs taken over time are in the patient. Photographs should be stored and presented appropriately for their use and images for publication should be prepared according to the instructions to authors. Digital images for publication should be sized appropriately for the final reproduction size. Keywords: Clinical photography, Medical photography, Standardisation Photographs can tell us a great deal about a patient's condition at an instant in time, and serial photographs taken over a period of time can tell us much more of the story, about the progress of disease or response to treatment. So why is it that the clinical photographs we see are so often a disappointment? Too dark, too light, dark shadows, unsharpness, colour variations, important detail obscured, untidy, indeterminate scale, serial photographs that don't match - these pictures are worth somewhat less than the proverbial 'thousand words'. Undoubtedly the best medical photographs are taken by fully-trained clinical photographers in professional studios with the full range of lighting and equipment available. But such a facility is not available to every clinician, and certainly not at all hours of the day and night or in every location in which they see patients. However, a number of conventions exist, which can be applied and adapted to improve clinical photography, even with the simplest equipment.[1],[2] We are not concerned here with photographic tricks, such as are seen in some advertising for anything from hair tonics to plastic surgery. Playing with angles of view, make-up and clothing, perspective tricks, soft focus and lighting can exaggerate the benefits of treatments on offer. Even more unscrupulously, images can be manipulated at the processing stage and this is both easier to do and harder to detect in digital images. There is no place in clinical recording or publication for using such photographic manipulation to misrepresent outcomes, and in some cases it would be illegal. We should be careful to ensure that we can demonstrate the provenance of our images: original films and written records should be retained, and for digital images an audit trail should be maintained.[3] It is axiomatic that the only variable among photographs taken to show change over time should be in the patient. Everything else should stay the same - viewpoint, positioning, lighting, colour, magnification, perspective, contrast, and background.[4],[5] The relative importance of these properties of a photograph might vary: colour might not always be important to an orthopaedic surgeon, although to a dermatologist it might be the most salient feature of a condition. However, the principles of standardisation should apply to any set of two or more photographs taken at different times. In practice it is extremely difficult to standardise absolutely so many variables - the photographs might be taken by different people, in different rooms, using different cameras, lenses or films, under different lighting, and from a different distance or angle to the patient. Slight variations in the film processing or digital treatment are highly likely. Different manufacturing batches of film will have variations in sensitivity and response to colour. Clearly, standardisation requires a certain amount of planning, a systematic approach, adherence to protocols and attention to detail.[6],[7] Much confusion can arise from photographs - particularly close ups - in which the patient's position, or the orientation of a body part, is ambiguous. If we are going to produce a serial record of a patient the positioning should be consistent.[8] The convention used by most medical photographers is, wherever possible, to photograph the patient in the anatomical position [Figure-1]. All clinical photographs should be viewed with reference to this position - the top of the photograph should always be nearest the top of the head. This works for most views but some parts of the anatomy are best viewed from other angles, or in different positions. The arms are best photographed in extension, and are normally photographed in a horizontal position. However, the palms should still face forward, so the back of the forearm should be photographed with the patient facing away from the photographer [Figure-2]. Close-up views can easily be misorientated, so should normally be accompanied by an 'establishing' view, to show their precise anatomical position. A full-length photograph of a patient is one of the most difficult to achieve satisfactorily. Fortunately, it is not often necessary or particularly useful, except to show abnormal stature, posture or body shape. The distribution of skin lesions is better shown with separate photographs from waist up, waist down, both front and back with the arms photographed separately. For some conditions it is preferable to show the patient weight-bearing. If the patient can stand unaided, they should do so in the anatomical position, as described above. While photographing the standing patient, remember that from your head position the patient's feet are a long way away compared to their head. This can cause both perspective distortion, with the patient appearing to have tiny feet and legs, and a dramatic fall off in exposure between the head and feet. You should position the camera level with the patient's mid-point - about waist level. It is difficult to produce satisfactory photographs of patients, other than infants and small children, in the prone or supine position. Such photographs require a greater working distance than can be achieved with the patient lying in bed - even if you stand on a chair or stepladder. A short working distance means using an extreme wide-angle lens, which will result in unacceptable distortion Babies, before they are able to sit or stand, can be photographed on a physiotherapy mat, or several layers of blanket, covered in a white sheet on the floor. Not only is this safer (they have nowhere to fall), but from a standing position you can achieve a full-length view without distortion. You will need the assistance of a parent or helper to position the child for lateral views, and to gently extend the legs to show his/her full length. The magnification of clinical photographs should always be controlled and standardised. This principle was firmly established in what have come to be known as the 'Westminster scales'.[9] This is, quite simply, a table of standardised scales for recording the commonest views of the human anatomy, which has been widely adopted by medical photographers and allows different workers to achieve closely matching magnifications in images of either the same patient over time, or different patients with similar conditions [Table-1].[10] The scales refer to primary magnification on the film itself, and apply to photography with a 35mm camera. They must therefore be adapted for digital photography where the light-sensitive chip in the camera might not be the same size as a 35mm film frame (usually smaller).[11],[12] There have been many adaptations where specific sets of views are required for a particular speciality, although few have been published.[13],[14],[15] This is a refinement of the principle, in which standard sets of views are agreed for recording patients undergoing a particular type of treatment. Such protocols can make photography a useful tool in treatment audit - such as standardised sets of views of patients undergoing plastic surgery. The best way to standardise scale is to use a lens that is marked with reproduction ratios on the barrel. The lens is set to a specific magnification ratio and focusing is achieved by moving the whole camera back and forward. Some lenses, such as the Nikon Micro-Nikkor lenses (www.Nikon.com), are factory marked for 35mm cameras, but for digital photography, using shorter focal lengths, either standardise on the marked distances or ascertain the ratios by photographing a ruler and mark the lens barrel with tape or thin paint lines. With simpler cameras, this approach might be difficult or impossible, but standardisation can still be achieved by maintaining the same distance from the patient. If the camera has a zoom lens, the amount of zoom should be fixed so that the image size remains the same at that distance. Some experimentation might be needed and cameras will differ in their ability to achieve this predictably. The addition of a linear scale gives a comparative method of assessing the size of a lesion - although caution should be applied to any attempt to take measurements from photographs: some distortion is inevitable, and it must be remembered that a single photograph is a two-dimensional representation of a three-dimensional subject.[16],[17],[18] In photographs for forensic or medicolegal purposes a 2-dimensional 'right-angle' scale is recommended.[19],[20] The perception of depth that perspective gives to a clinical photograph is an important attribute. The concept of diminishing image size with distance is familiar, but perspective also affects the appearance of objects and people as viewpoint changes: come too close and features can appear distorted, but take the photograph from too great a distance and the perception of depth is lost.[21] That is why not only the image size, but also the distance from which a photograph is taken, should be standardised [Figure-3]. For 35 mm film, a lens of around 100mm focal length allows distortion-free images in most clinical situations, but a shorter focal length of around 50-60mm will be needed for full length photographs, or when working in a confined space. Depth of field is the amount of a subject that appears sharp in front of, and behind, the principal plane of focus. The smaller the lens aperture, the greater the depth of field, and this is particularly critical in close-up work where there is considerable depth, such as when photographing the teeth. Relative aperture size is denoted on a lens by f-numbers - the higher the number, the greater the depth of field, but the smaller the amount of light passed through the lens. Generally in clinical photography we need the maximum depth of field so our flash should be bright enough to allow us to use the smallest possible aperture. On 35mm cameras we should aim for at least f/16, and up to f/32 for close-up work where depth is important. Using a faster film will improve depth of field, but at the expense of some image quality (see Cameras, film and Processing, below). Our eyes and brain have an extraordinary ability to adjust to different lighting conditions - we work quite happily in daylight, or under tungsten and fluorescent lights. Cameras and films are less adaptable, particularly in mixed light, so photographs taken with a daylight film in fluorescent lighting will have a green cast, while those taken in tungsten lighting will have a strong orange/ yellow cast. Indoor lighting is not bright enough and the quality of the light is never appropriate for clinical photography. Electronic flash ('strobe' in USA) is ideal for providing a bright light source that is of such short duration that it is capable of 'freezing' any movement. It is powerful enough to negate the effects of normal room lighting, although if you work in a room with strong sunlight coming in through the windows, you should close your blinds or curtains. Similarly, powerful examination lights or operating lights should be dimmed while taking photographs with flash. Modern compact cameras have a flash built into them, usually with automatic exposure control, making it difficult to produce a badly-exposed photograph. This is fine for a quick record, but the lighting is too close to the lens axis to provide sufficient modelling effect to demonstrate shape and texture. It will also produce 'red eye' - the red reflexes you see in people's eyes in photographs taken with compact cameras (red-eye reduction modes use a pre-flash, which causes a delay in the shutter firing, so are not ideal for moving subjects such as lively children). A still photograph doesn't have the advantage one has in a live examination, of moving oneself or the patient to look at a subject from any angle. Shape and texture can be revealed by off-axis lighting from a portable flashgun held in the hand that is not holding the camera, or attached to a bracket. Ensure that it is pointing directly at the subject, to avoid the light falling off toward the edges. Lighting should as nearly as possible replicate what we are used to seeing: light from the sun, or indoor lighting from the ceiling, throwing shadows downward. Lighting should therefore come from above, and not below, in relation to the 'anatomical position' in which we pose the patient. Getting this wrong can have strange effects [Figure-4]. There is a common misconception that all medical photographs should be taken with a ring flash. The ring flash is an important tool for photographing cavities, where the shadow of a directional flash would obscure important detail. Thus, it is useful for dental photography, or for deep wounds in surgical photography. A ring flash provides virtually shadowless lighting, with the flash tube wrapped around the camera lens. This type of lighting is very flat and reduces modelling. It also causes large circular reflections, which are particularly noticeable on wet surfaces such as the eye. For this type of work, a hand-held flash is preferable: a powerful light source providing modelling and a single, small reflex [Figure-5]. Photographs that are too dark or too light are a bitter disappointment, and clinical photography presents greater challenges than almost any other type of photography. Clinical detail is easily lost in washed out pale skin or underexposed dark skin. The extremes of light and dark in specialities such as dental or operative photography can disrupt the most sophisticated light metering systems. It is really worthwhile doing some tests for your camera/ flash/ film combination with different subject matter. Pre-determined exposures that can be manually set for any magnification ratios are more reliable than automatic exposure meters, because automatic metering can be influenced by the background to cause the area of interest to be incorrectly exposed.[22],[23] Occasionally, it might be useful to include contextual information in a photograph, such as showing the patient sitting up in bed, or attached to equipment. Similarly, if the photograph is to show dermatitis caused by an elasticated bra strap, it might be useful to include in the photograph the item of clothing responsible. In most cases, however, we are interested only in the clinical appearance of the patient, so all other distractions and possible influences to judgement should be excluded from the image. Untidy backgrounds should be avoided. Coloured backgrounds can reflect onto, or throw a cast of the complementary colour into, the subject, so the background should be neutral white or grey. If you routinely photograph patients in a clinic or study it is worth fixing up a plain, neutral background sheet. Professional medical photographers often prefer to use a black background, which requires several carefully-placed lights to ensure that the edges and hair of the patient are not lost in the photograph. When photographing patients in a ward it is best to place them against a plain white sheet. Use sticky tape, velcro or bulldog clips to suspend the sheet and smooth it out as evenly as possible. A white pillow will suffice when photographing someone in bed. Use a chair with an adjustable back to pose the seated patient and exclude any parts of the furniture from the frame. Remove jewellery and make up as far as possible. Allow patients time to replace them in private afterwards, and provide a mirror for that purpose. Ideally, all clothing should be removed from the field of view. This clearly requires some sensitivity and tact, as few people are used to exposing themselves to a camera. Ask the patient to remove only the parts of clothing appropriate for each picture, rather than leaving them exposed any longer than is necessary. Photographs of patients hitching up their clothing can appear less dignified, less clinical and probably cause the patient no less discomfort than if they removed those items completely. Modesty garments can be worn if it is not necessary to show the genitalia; disposable white underwear should be available, or use small sheets held up with tape or bulldog clips. Any extraneous items of clothing appearing at the edge of the frame should be cropped out afterwards.[24] If the patient is assisted, for example a child held by a parent, care should be taken to avoid including that person in the photograph. While photographing a child on a mother's lap, ask her to sit sideways on, so that she is not seen behind. Keep helping hands out of frame, or be as discreet as possible. In close-up photographs, where a hand is seen retracting eyelids, lips, etc., ask the person who is doing the retraction to wear an examination glove. The distraction of a patient or parent's dirty fingernail in the field of view can ruin an otherwise excellent close-up view. Hair should be swept back from the face, using a hair band and/or hairclips. Hairclips can also be used to expose lesions on the scalp to best advantage. While photographing the lateral aspect of the head, long hair should be swept over the opposite shoulder, or held up in a bun. In choosing a camera for clinical photography, the two main choices are between digital and conventional film and between compact and single-lens reflex (SLR) cameras. Your choice will depend largely upon your budget, and just how portable you need the camera to be. One of the biggest attractions of digital cameras is their immediacy. After taking a photograph you can check to see whether you have a useable image, and you can download photographs onto a computer within minutes. There are hundreds of digital cameras in the market, presenting a confusing range of choices. If you want a compact camera that fits neatly in your pocket or medical bag, you will have to make compromises in the control you have over lighting, image size and working distance. Greater control can be achieved with an SLR, which will allow you to change lenses and attach different types of flash. However, digital cameras of this type are prohibitively expensive and are used mainly by professional photographers. The alternative is to use a conventional camera and have your slides or negatives scanned. Many processing laboratories will process and scan a film as a routine service, giving you a CD of all your images, sometimes in several different resolutions. Furthermore, colour negative film is more forgiving of slight exposure variations than slides or digital cameras. In all that we have heard about the progress of digital photography, something that has gone relatively unnoticed in recent years is that photographic films have improved dramatically. There has always been a compromise between light sensitivity (film speed) and sharpness or grain in a film, but modern films have exceptional quality, so we do not have to make such big compromises. Faster films are particularly important when doing extreme close-up photographs, or with a relatively small on-camera flash at greater distance, such as when taking a full-length photograph. ISO 100 is fast enough for most modern flash sources and ISO 200 should normally be regarded as the maximum. Processing should be carried out by a professional laboratory that has strict quality control and will agree to confidential processing arrangements.[25] Specialist clinical photography requires more specialized equipment and techniques, a full description of which goes beyond the scope of this article. For dental photography a range of mirrors and retractors is essential. Ophthalmic photography uses sophisticated slit lamp and retinal cameras, with which investigative photographs can be taken, such as fluorescein angiograms. Endoscopic photography uses cameras designed to attach to the instrument. Most instrument manufacturers supply, and can advise on, proprietary recording systems. Orthopaedic patients might present handling problems, requiring special chairs and other equipment. In dermatology, some conditions can be photographed in the invisible spectrum, using infrared, ultraviolet or fluorescence techniques. A useful source of information is the RMIT's Medical and Scientific Photography website: http://msp.rmit.edu.au. Consideration should be given to the conditions for viewing images. Clinical photographs might be seen as prints in a patient's case-notes, as digital images on a computer screen or, more rarely these days, as projection slides. Prints should be viewed in good lighting - preferably daylight or 'white light' fluorescent illumination. Ask your laboratory to print photographs on glossy, rather than matt or textured paper. Prolonged exposure to ultraviolet rays will cause fading and colour change, so keep prints stored out of direct light, preferably between sheets of acid-free paper. Slides are better for group viewing and, with consistent processing in a good laboratory, can give quite consistent results. Store them in archival-quality polypropylene filing sheets to avoid chemical damage. Computer viewing and projection of digital files can present problems of both quality and consistency. Use a good quality monitor positioned away from brightly-lit windows or coloured surrounds. The most important factor to control in viewing is consistency. Use a good professional laboratory for films and do not leave films in the camera for months before processing - both exposed and unexposed film deteriorates over time. Keep your films in a cool place. Store large batches of unexposed film in a refrigerator, but remove it at least an hour before use to allow it to return to room temperature. Digital files for projection should be saved as high-quality JPEG (.jpg) files, but most publishers prefer TIFF (.tif) files. The file size will depend upon the reproduction size and many publishers will state exactly the file size to submit. It is normally safe to save them at a resolution of 300 dpi (dots per inch) at the final reproduction size. Check recent issues of the journal to see what is the maximum size at which images are normally reproduced (usually defined by the column width). Some useful advice on submitting photographic prints is given on this journal's website - www.jpgmonline.com. Familiarity with equipment and adherence to simple protocols can make all the difference between success and failure in clinical photography. A systematic approach is essential. This should extend beyond the photography itself to the handling and storage of photographs. Considerable attention should also be paid to legal and ethical issues before undertaking any clinical photography. The Physician's Handbook of Clinical Photography by Stack et al gives useful advice on photographing different parts of the body.[26]
Copyright 2003 - Journal of Postgraduate Medicine. Online full-text also available at http://www.jpgmonline.com/ The following images related to this document are available:Photo images[jp03070t1.jpg] [jp03070f4.jpg] [jp03070f5.jpg] [jp03070f1.jpg] [jp03070f2.jpg] [jp03070f3.jpg] |
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