Reducing patient exposure while maintaining image quality in radiology

Radiology, Reducing Patient Exposure and Maintaining Image Quality

Radiology as a branch of medicine was born due to the pioneering effort of German physicist Wilhelm Roentgen who accidentally discovered X-rays while researching in his lab in 1895. The amazing benefit that X-rays offered to medical science was recognized and, with the research of French scientists Marie and Pierre Curie after the discovery of Roentgen, scientific and technological developments have resulted in the vital contribution which radiology has presently come to offer in the diagnosis and treatment of various ailments. Radiology is a diagnostic as well as a therapeutic instrument. In order to recognize diseases and other conditions inside the human body, diagnostic imaging makes use of several varied modalities like plain radiography, CT scanning, Magnetic Resonance Imaging -- MRI, ultrasound, and nuclear medicine. Therapeutic imaging, usually known as interventional radiology happens to be a subspecialty which entails the application of imaging technology to undertake invasive methodologies that are least invasive with devices such as catheters, balloons, and stents to free congested blood vessels, drain fluid, and also carry out needle biopsies. Radiology imaging studies are normally done by a skilled technician in radiology while the radiologist, a specially qualified medical doctor, evaluates and reads the radiographic images and submits the results to the doctor in charge of the primary care of the patient. Presently, the science of radiology is on the threshold of new chapter. Technological advancement related to computerized data has facilitated the efficient reach of diagnosis and treatment in favor of patients across the world cutting across geographical barriers.

The use of technology for visualization of the body:

Images that are taken of the human body play a central role in the usual clinical practice at the moment, not merely in the diagnosis of a lot of diseases but also in subsequent stages and treatment of patients. Following the discovery of X-rays, physicians started it as a noninvasive procedure to see inside human bodies. It is an accepted fact that x-rays comprise of electromagnetic radiation. The radiological image is produced by the darkening of a film by the radiation transmitted across the human body. Conventional radiation delivers an image of objects in a two-dimensional or 2D plane. Even though it was the foremost method of imaging to be developed, it still continues to be the usual type of radiology. The films created by X-rays reveal various features of the body in different shades of gray. The gray becomes darkest in those regions which do not absorb X-rays, while the lighter shades are seen in dense areas.

Even though Radiology started with the application of x-rays and huge flat sheets of photographic films, the modern Radiologist is equipped with a lot of instruments for taking images of living patients. A lot of these modern instruments build an image with the help of a computer which is CT or computed tomography and some do not make use of any x-rays, nor any radiation of any type such as Magnetic Resonance Imaging --MRI and Ultrasound.

Different types of Radiography:

i) Plain radiographs: Under this procedure plain x-rays are obtained through the application of different imaging techniques, and they all need exposing the patient to X-ray radiation. The image is essentially a shadow of the parts of the patient which absorb or block the X-rays. The image can be collected on a photosensitive film, on a digital imaging plate, or on a fluoroscope. The image is a "photographic negative" of the object with the "shadows" being the white areas that have been blocked by the object. Plain radiographs or plain areas are generally taken by skilled registered radiologic technologists. The films are thereafter read by the qualified Radiologist in order to make a diagnosis. An image of Plain Radiography is shown in Exhibit I.

A ii) Fluoroscopy: This is a method for seeing "live" X-ray images for a patient. The Radiologist makes use of a switch to regulate an X-ray beam which is transmitted through the patient. The X-ray thereafter hits a florescent plate which is coupled to an "image intensifier" which in turn is coupled to a television camera. The Radiologist can subsequently watch "live" images on a TV monitor. The use of fluoroscopy is regularly made to observe the digestive tract. The Upper GI series is Barium Swallow while the Lower GI series is Barium Enema or "BE." The colon becomes visible on the BE. The white areas are barium contrast, while the black regions are air. An image of Air-contrast Barium Enema is shown in Exhibit - II. The application of Fluoroscopy is also made in a lot of diagnostic and curative methods in order to observe the action of instruments that are being used either for diagnostic or treatment of patients.

A iii) Angiography: Under this procedure X-rays are used for the generation of picture which is the angiogram. This is an invasive radiology procedure as it needs the patient to be injected with a radiopaque substance i.e. It absorbs X-rays which is generally known as a contrast agent or a dye. Normally a very tiny tube with a special shape is used to put the contrast into a specific artery or vein. As the artery or vein has this radiopaque material, it will obstruct the X-rays, and in the process will cast a shadow of the injected vessels on the X-ray film or fluoroscope. This image will display the shape of the artery and can assist in the diagnosis of an obstruction, blockage, or constriction of artery. An image of angiography of the skull is shown in Exhibit III.

A iv) Computed Tomography:- Computed Tomography is popular by the name of CT or CAT Scans. Computed Tomography is a specialized X-ray imaging technique that may be conducted "plain" or following the injection of a "contrast agent" CT constructs the image through the use of a collection of individual small X-ray sensors and a computer. Through spinning the X-ray source and sensor/detectors around the patient, the data is collected from different angles. The information is then processed through a computer to create an image on the video screen which are known as 'sections' or cuts as they show to look like the cross-sections of the body. This process does away with the problem of a conventional X-ray, in which all the shadows overlap. A CT image is shown in Exhibit IV.

A v) Ultrasound (U.S.): Medical U.S. applies high frequency sound waves to create an image of living tissue based on the identical technique of weather radar and submarine ultrasound. Through transmission of sound signals and using the reflected echoes, images are created. U.S. As against majority of the other imaging techniques are capable of creating precise real-time sequences of the beating heart, bowel contraction which is known as peristalsis. U.S. can also show the speed of blood flowing through the use of Doppler and it can be measured and illustrated through the use of color pictures. The entire procedure is non-invasive without causing any harm to the patient. Through the use of Doppler Technique, Radiologists detect the presence of blockages in blood vessels in the neck and other regions. One of the most common U.S. procedures is the examination and periodic monitoring of the living fetus growing inside the mother's womb known as Obstetric Sonography. An U.S. image is shown in Exhibit V.

Magnetic Resonance Imaging (MRI): MRI does away with the use of X-rays or any category of "ionizing" radiation. As an alternative, it is a methodology that combines a large magnetic field and some RF antennas. The image is formed as the resulting image mainly reflects the water protons in the patient as also their chemical associations with protein. A MRI image is shown in Exhibit VI. Neuropathological contribution in head trauma has stressed on the distinction between focal and diffuse injury. Focal injuries caused due to hematomas and contusions while neuropathological researches have revealed the significance of microscopic diffuse axonal injury in patients who lost their lives after injury. Injury because of secondary hypoxia and ischemia can also result in focal and diffuse patterns of lesions. The difference between focal and diffuse injury is sometimes applied in favor of survivors. It has been observed that MRI is more sensitive to traumatic brain damage compared to Computed Tomography -- CT. A lot of head injury survivors have seen to sustain multiple lesions in frontal and temporal areas. Legions inside the brain stem and corpus callosum are sometimes also seen on MRI and are most probably manifestations of acute diffuse axonal injury. The subsequent psychological results of diffuse and focal injuries are not properly intelligible and constitute a matter of debate. The neuropathological view emphasizes the vast significance of diffuse axonal injury, instead of focal injury, in finding out the consequences of head injury.

Patient Exposure and its reduction in Radiology:

Through the use of digital techniques potential exists to enhance the practice of radiology, but there is also the inherent risk of overuse radiation. The main advantages of digital imaging constitute wide dynamic range, post-processing, different viewing choices, electronic transmission of reports and documenting possibilities are there, but overexposures can happen without a bad impact in the quality of the image. Under conventional radiology, excessive exposure outputs a "black" film. In case of digital systems, good images are got from a large range of doses. With the help of digital fluoroscopy systems, it is extremely simple to get as well as delete images. There might be an inclination to get more images than what is required. In case of digital radiology, higher patient dosage implies improved image quality and therefore a propensity to apply higher patient doses than is actually needed. Different medical imaging works need different intensities of image quality and due to that doses that have no extra benefit for clinical purpose are avoided.

The quality of image can be affected through lack of correct levels of data compression and also post processing techniques and all these new challenges must be part of the optimization process and covered in the clinical and technical protocols. Local diagnostic reference levels must be reassessed for digital imaging and patient dose constraints must be shown at the console of the operator. Frequent patient training must be done at the time when digital methodologies are launched. Rendering training in managing image quality and patient dose in case of digital radiology is essential. Digital radiology will entail new laws and present new challenges in case of practitioners. Since digital radiology images are simpler to get and to communicate the justification, standards must be strengthened. Installation of digital systems must entail clinical specialists, medical specialists as also radiographers to guarantee that imaging potential and radiation dose management are dovetailed.

The biggest single man-made source of X-ray happens to be medical diagnostic radiography. Latest estimates have stated that the X-ray examinations constitute the reason behind the maximum of the total effective-dose-per-capita irradiation. The diagnostic nuclear medicine procedures are responsible for more radiation. It is normally consented that medical X-ray exposure can be lowered considerably without lowering the quality of radiological images. Hence it is important that patients are not exposed to unnecessary radiological examinations, and are safeguarded from greater degree of exposures when the radiological methods are needed. A lot of major dose surveys have been undertaken particularly in the developed nations. In 1991-92, Harison et al. undertook a pilot study through the application of indirect methods to examine the capability for reducing the radiation dose to patients and to made recommendations on efficient procedures. Even though it is restricted to quality control activities like tube potential (kV), mAs, sensitometry, and image quality tests, the gravity of patient dose monitoring was also identified as a vital aspect of the entire program. In the initial survey, the entrance skin exposures -- ESEs of the average size patients for the routine radiographs in public hospitals were conducted.

In the study it was observed that very wide variations of the patient dose in the identical X-ray examination in the different hospitals. Some of the factors that were responsible to the observed radiation in the patient exposure can be ascribed to the application of lack of optimal imaging devices, substandard choice of technical factors and wrong film processing methodologies. Therefore it is suggested that a considerable reduction in the doses of radiations can be done without seriously impacting the quality of image. Use of fast film-screen combination was possibly one of the major factors in lowering the ESE by 30 to 40%. Nearly, the entire radiology centre taking part in the study was making use of the combination of fast film-screen and good quality development drugs. Therefore the patient dose spread was primarily because of the choice of exposure factors, focus film distance and output of the X-ray units.

Since the chest and skull mAs and kVp in the first study was respectively higher and lower compared to the NRPB calibrations, it has been suggested that they raised kVp and lower mAs. These alterations would raise the patient dose without significant impact on the quality of the image. It has also been calculated that raising the tub potential from a value of 600 to 90 kVp will outcome in an ESE savings of 60%. It was discovered by Matrin et al. that raising the tube potential by 8-13 kVp in the lumbar and thoracic spine tests resulted in dose reductions of 26-30%. In the experiments it was also observed that the lowering in mAs lowers the film optical density and patient dose by a factor of 10 to 50% without obviously lowering the quality images. It implies that the contrast or resolution of a white radiograph might be equal to that of a black radiograph.

Use of digital imaging for enhancing image quality:

With massive technological development in the digital imaging, Picture Archiving and Communication Systems -- PACS has been a contributor in enhancing image quality in Radiology. However, maintaining PACS and clinical workstations comes under the purview of the overall hospital information technology management program. Whereas this condition in the majority of the situation happens in the clinical areas outside of radiology in which several multi-use Personal Computers are also used as image display devices, this state of affairs is more and more usual in the radiology environment wherein PACS workstations are managed as high-end computers in place of medical display devices. A large number of differences in the data sets exist that are created by different image acquisition systems that should be given room in case the spread of digital imaging across specialties has to progress in the absence of spawning severe negative side effects. For instance two instances can be given in which such problems crop up. (i) an ER doctor using the display monitor of a laptop computer for diagnosing a possible pneumothorax and (ii) a pulmonologist using a standard 1.2 megapixel (MP) display monitor to view the chest images to find out the presence of lung modules. In case of the above examples, the risk remains that the two physicians will not be able to see fine image details which are present in the image data sets as the display device will not be capable of producing them in a humanly intelligible way.

The two important factors in a display device happen to be spatial resolution and contrast resolution. The spatial resolution is found out by how many pixels a display device has, whereas the contrast resolution is found out by the brightness range of the monitor along with the application of DICOM calibration. Users of display and managers of medical display technology must be acquainted with these concepts and make application of that knowledge to the correct procurement, installation, and servicing of medical displays. Different doctors apply different data types and thus need different display devices. Apart from that, some physicians provide diagnostic reports or make treatment decisions based on the data they observe and, thus must have their monitors optimized to that assignment while others make application of images and the reports together as data points in a differential diagnostic process and are not in need or highest quality of image display. It is also crucial to consider safety concerns related with all equipment, particularly instruments in operating rooms, treatment rooms, procedure rooms, trauma rooms as well as ICU patient rooms. One recent phenomenon has been teleradiology that allows doctors to review images from home during emergency situations which also requires correct displays. Installation of a high-end laptop computer with a DICOM-calibrated high-resolution display can also be used.

Display devices contribute significantly in a lot of areas of healthcare and the absence of knowledge regarding the differences in image quality of display devices are areas of concern for the medical profession. Display broadly falls into two broad categories viz 'diagnostic' and 'review' which might also be referred to by the alternative names such as 'primary' and 'secondary'. Diagnostic displays are used for making a primary diagnosis and also for the purposes of displaying an image on which a report will be based. Review displays are used for display images for purposes apart from making a primary diagnosis and therefore the needs of these displays are less severe compared to those for primary displays. As regards maintaining display quality, it needs to remain at the specified settings and must not degrade in the course of time. The factors are focus, luminance, and contrast and color rendition. It is important to note that display devices must have limited user access to controls in order to check brightness and contrast being adjusted by the wrong personnel. Displays regardless of monochrome or color, might require color matching when used in groups. Review quality display devices do not require the identical level of image quality assurance as diagnostic displays. Nevertheless, they require cleaning and the image quality checked that could be attained with in-house trained staff. Care must also be given to display monitors used for instance at the homes of clinicians for remote reporting or review.

Latest developments in image enhancement:

lot of institutions have replaced traditional Cine Angiography -- CCA which makes use of 35mm conventional cine-film with filmless digital cine angiography -- DCA. Digital cardiac and coronary angiographic systems make use of video camera to obtain an electronic video image from the x-ray image intensifier. In CCA systems, the image intensifier converts x-ray into a visible light which is entered into a video camera and also a cine camera at a ratio of 10:90 (or20:80). The dose of radiation in digital angiography systems in the absence of cine camera might be reduced as compared to that in CCA systems. But too much reduction of dose induces a rise of quantum noise from the generation of X-rays and lowers the quality of image. The radiation dose reduction should not outcome in degradation of the quality of the diagnostic image, instead the image quality of digital cine images must be equal or superior compared to old cine films. Following investigation it was decided that the degree of radiation needed in DCA systems that can be lowered while maintaining image quality at par with that of CCA.