What is Medical Imaging and Radiation Sciences?
Radiographers are health professionals who facilitate patient diagnosis and management through the creation of medical images using X-rays, ultrasound and magnetic resonance. They play a pivotal role in selecting and implementing the most appropriate examination protocols which will answer the clinical question. Radiographers are obliged to act in an ethical and professionally responsible manner and exhibit a high level of communication skills. When utilizing x-radiation radiographers must implement appropriate radiation protection measures and act at all times to keep the radiation dose as low as practicable. Radiographers work in collaboration with radiologists and other specialist medical practitioners to provide patients with a range of diagnostic examinations.
The creation of the familiar plain radiograph begins with the radiographer receiving a request form for a radiographic examination of a particular part of a patient's body. The next phase involves the radiographer assessing the patient prior to selecting the most appropriate imaging equipment and positioning methods for the projections that will best answer the clinical query. Essentially the radiographic procedure involves the selection of exposure factors and the accurate positioning of the patient's body in relation to the x-ray tube and the imaging device. Today the imaging device will either be a conventional x-ray cassette and x-ray film which will be developed photographically or a digital plate which will be computer processed. Prior to sending the radiographs or images on for reporting by the radiologist, radiographers must evaluate their radiographs or images in terms of image quality, radiographic positioning and the clinical question. This means radiographers need a high level of knowledge about the science of image formation, radiographic anatomy and pathophysiology. This aspect of radiographic practice is covered in the first three semesters of the Monash course. However, due to the complexity of the human body, illness and disease and the range of patients requiring radiographic services students engage in general radiography throughout the course.
Traditionally fluoroscopy is an imaging method that uses x-rays and closed circuit television to produce "real time" images of the body. Typically in clinical radiology departments fluoroscopy is used to image the digestive tract and the hepato-biliary system and genito-urinary system. In these cases radiographic contrast agents must be introduced into the patient in order to visualize organs that are normally only seen as shadows on a plain radiograph of the abdomen. Increasingly tradition fluoroscopy is being replaced with digital systems that enhance its diagnostic capacity whilst reducing overall exposure levels. The mobile versions of the fluoroscopic system are used extensively in the operating theatre to assist surgeons to evaluate a wide variety of operative procedures. Students study the principles and practice of fluoroscopy in first semester of second year with study in digital image processing commencing in second semester of second year.
Computed tomography (CT) is an integral component of the general radiography department. Unlike conventional radiography, in CT the patient lies on a couch that moves through into the imaging gantry housing the x-ray tube and an array of specially designed "detectors". Depending upon the system the gantry rotates for either one revolution around the patient or continuously in order for the detector array to record the intensity of the remnant x-ray beam. These recordings are then computer processed to produce images never before thought possible. The familiar radiograph lacks a third dimension; it can only show us a two-dimensional view of the human body. CT on the other hand reconstructs images in a variety of body planes the most usual being the axial or cross sectional plane. The image created displays CT numbers which mainly reflect the physical properties of the tissues being investigated. Because of the large range of the CT number scale and the fact that the image is digital, it is possible to manipulate the display to show the underlying soft tissues with enhanced contrast as well as the bony structures. Technological innovation has been a continuous feature of CT since its invention in 1971. Scanners today are capable of gathering even more data about the body structure in a time span that is measured in seconds thereby enhancing its clinical usefulness. CT innovation has meant radiographers today need to be able to recognize and evaluate anatomical structures in a variety of body planes. Study of cross sectional anatomy and pathology and CT are part of third and fourth year of the Monash course in Radiography and Medical Imaging.
Ultrasound imaging is another of the many 'modalities' that is encountered in the imaging department. Its distinctive feature is that it uses high frequency ultrasound to construct an image rather than the traditional x-ray. This means that it is a safe, non-invasive means of creating cross sectional images of the human body. It is also a relatively cost-effective means of imaging. Ultrasound is familiar to us all because of its role in obstetrics. Nearly all pregnant women, at some stage, experience the delight of seeing their developing fetus with this technology. While this is going on, they also experience an important medical test which will assist their management. Ultrasound however is used with great diversity beyond obstetrics. Vascular ultrasound, for instance, allows us to see the blood flow in real-time thus making it possible to discern stenoses in the arteries, or thrombosis of the veins. Musculoskeletal ultrasound allows us to image tiny tendons and nerves for degeneration or tears. Ultrasound is used in abdominal, gynaecological and paediatric assessment. The technology is enabling us to see the movement of organs, see their structure in 3D, and image their microvasculature.
Ultrasound imaging is performed either by a medical physician or a sonographer. The sonographer gains their accreditation through the Australian Sonographer Accreditation Registry (ASAR) after obtaining a two-year part time, Graduate Diploma in Medical Ultrasound. This is available through our department. Because of the emphasis upon sonography in the Bachelor of Radiography and Medical Imaging graduates with good grades in the sonographic units are eligible for exemption from several of the level one units in the Graduate Diploma. Sonographers work in multi-modality imaging centres in hospitals and private practices. They also work with specialist physicians such as obstetricians and vascular surgeons. Sonographers are involved in diagnosis and imaging.
Mammography uses dedicated, low-dose X-ray equipment, to obtain images of the breast to assist in the diagnosis of breast cancer and other breast diseases. This is available to women through the Breastscreen Program and in Diagnostic Imaging facilities in both Public and Private Imaging Departments. Students in the third year of the Medical Imaging and Radiation Sciences course are given an understanding of the imaging process, the anatomy and pathology of the breast and an insight into the highly specialized communication and interpersonal skills required when dealing with both male and female patients and the diagnosis of breast disease.
Magnetic Resonance Imaging or MRI
This is an advanced and specialised field of radiography and medical imaging. The equipment used is very precise, sensitive and at the forefront of clinical technology. MRI is not only used in the clinical setting, it is increasingly playing a role in many research investigations. Magnetic Resonance Imaging (MRI) utilises the principle of Nuclear Magnetic Resonance (NMR) as a foundation to produce highly detailed images of the human body. The patient is firstly placed within a magnetic field created by a powerful magnet. The hydrogen atoms in the human body (we are made up of H2O) then align themselves with a North and South orientation within this magnetic field - that is, they behave like tiny bar magnets. Using a transmitting device, the radiographer transmits a radiofrequency (RF) pulse. This causes the hydrogen atoms to alter the direction of their orientation. The transmitting RF pulse is switched off and the hydrogen atoms begin to return to the alignment they acquired when they were first placed in the magnetic field. As this re-alignment occurs they emit an RF signal which is detected by a receiving device or antenna. From this received signal, sophisticated electronic and computer equipment is used to determine the intensity of this signal and the exact location from where this signal originated. From this viewpoint, the computer performs advanced image reconstruction calculations and produces an image that can be viewed, hard and/or soft copied and interpreted for any diagnosis. The images can be acquired in a variety of planes, commonly, sagittal, axial and coronal (also oblique planes can be performed) - while the patient is lying still in the same position.
Digital Vascular Imaging
This is an imaging modality that utilises the technology of digital fluoroscopy and additional equipment and computer systems to image the blood vessels (arteries and veins) of the human body. The images produced serve a diagnostic purpose; that is, diagnosing a pathology or condition. Also, treatment or therapeutic cases can be performed such as stenting (inserting a device into a blood vessel in order to keep it open and allow blood to flow through) or infusion of thrombolytic agents (administering a medication such as Urokinase to help breakdown a recently formed thromus or blood clot). The procedures are performed under sterile conditions and require that the patient be fasted (no food prior to procedure) and the radiologist or cardiologist (the specialist medical practitioner who performs the invasive procedure and subsequently interprets the images) be "gowned" as in an operating theatre. Specialised DVI suites are used to image the blood vessels supplying blood to the heart itself. This modality requires that the radiographer is part of a team approach working closely with other health professionals such as radiologists, cardiologists, nurses and cardiac technicians.
DEXA is a dual energy X-ray absorptiometry imaging technique widely used for non-invasive assessment of bone mineral content. This has a direct impact on the management and treatment on the condition of osteoporosis. Osteoporosis, within our community, continues to debilitate those with the condition and presents a large problem for those with an increased risk of fracture. This imaging system allows for early detection of the condition and acts as a baseline study for future following preventative management and treatments.
Radiation Therapy is a highly specialised area of the radiation sciences. It is a scientific and clinical profession dedicated to the management of patients with benign and malignant disease.
The ionising radiation in its commonest form for treatment is photons (x-rays). The radiation can be used on its own, or in combination with other cancer management strategies such a surgery or cytotoxic chemotherapy. This depends on many factors including the histological diagnosis, how advanced the disease is and the health of the patient.
The radiation can be delivered with one of two intensions radical and palliative. Radical intent is where high doses of radiation (depending on the histological diagnosis) are delivered with the intent to cure, and palliative intent is treatment in order to provide relief from cancer symptoms. One of the main considerations in managing cancer with radiation (as with any other treatment) is maintenance of quality of life for the patient.
The following steps constitute the radiation therapy process:
This is the initial step in the radiotherapy process. At this point the exact position of the tumour is located by utilising diagnostic image acquisition techniques such as plain radiographs, CT, MRI and PET. Simulation of the treatment area may also occur where the treatment ‘set up’ is reproduced and radiographic images of this are acquired and recorded. These images are then interpreted and used to configure individual treatment plans for each patient and also for comparison during treatment itself.
Integration of the above modalities in the localisation of the treatment ensures that even microscopic tumour cells and/or lymph nodes that are positively identified as having tumour present are included.
The tumour/site of original tumour and an area of tissue surrounding it are treated to the highest possible dose. This combined site of tumour and normal cells is known as the Tumour Volume.
Radiation therapy planning utilises sophisticated computer systems to maximise tumour dose and minimise the dose to healthy surrounding tissues. A computer is used to generate a pictorial arrangement of the distribution of the radiation dose that the tumour and surrounding organs will receive. This is imperative because organs such as the spinal cord or lungs can only tolerate minimal doses of radiation before irreparable damage occurs.
For any one particular treatment site the radiation beam can be directed towards the patient from a number of angles (fields) in order to reduce the dose to radiosensitive organs and ensure a high dose region around the tumour volume.
There are a variety of radiation modalities available for treatment. The choice of radiation/particle type (photon, electron, proton, neutron, beta and gamma) and energy depends on a number of factors such as how ‘deep seated’ the tumour is and the nearby radiosensitive structures.
Radiation can be administered externally with machines that work at either Kilovoltage energies (used for treating superficial tumours) or Megavoltage energies (Linear Accelerators which are used to treat deep seated tumours).
Daily treatment has to be both accurate and reproducible. This means that the patient needs to be immobilised in exactly the same position every day. Precise measurements are used to align the radiation beam with the specific area of the body being treated. The treatment area itself can be verified on the treatment machine before, during or after the daily treatment is delivered. These images can then be matched with those from the original planning procedure using sophisticated computer equipment.
Prior to any patients being treated all equipment must go through rigorous quality assurance procedures in order to ensure it is operating safely.
The technology within the field of radiation therapy is constantly developing with the view of achieving optimal conformation of the radiation beam to the tumour volume. Utilisation of Intensity Modulated Radiation Therapy (IMRT) is the closest the technology has got to achieving this.