Types of Medical Scanners
What is medical imaging?
Medical scanners are used to produce pictures of the human body. These images are utilised by healthcare professionals to evaluate and assist in the diagnosis of a disease state. This allows for the development of a personalised treatment plan for the patient. In addition, medical imaging is also used to monitor patients for any future medical difficulties that may develop over time. This is in conjunction with regular health screening programmes.
Since the discovery of X-rays, radiologists can image the human body in sophisticated detail with a wide array of medical imaging scanners. These modalities include computed tomography (CT scanner), magnetic resonance imaging (MRI scanner), positron emission tomography (PET scanner), ultrasound scanner amongst other techniques.
Various screening programmes are used by healthcare organisations; for example, for the detection of breast cancer by the use of advanced positron emission mammography (PEM). Subsequently, the technique called dual-energy X-ray absorptiometry (DEXA) is used to investigate osteoporosis and monitor the mineral density of bone. The most popular and widely used imaging modality is ultrasound, which can be used to examine the liver and kidneys, in addition to muscles and joints.
Currently, medical imaging plays a vital role in the evaluation of various heart conditions through cardiac imaging. This article aims to give patients a brief outline of the different medical imaging modalities which are used in hospitals and healthcare organisations.
What is an X-ray?
In 1895, Wilhelm Conrad Röentgen was working in his laboratory at Würzburg University in Germany, when he observed crystals near a high-voltage cathode-ray tube beginning to glow. He concluded that a form of energy was being generated by the cathode-ray tube -which was able to penetrate the nearby paper – causing the crystals to glow. Röentgen named the unknown energy ‘X-radiation’.
X-rays are now a general medical diagnostic procedure used to obtain images from inside the human body. The X-ray procedure only takes a few minutes – with the significant advantage of this imaging technique being that the X-ray machine does not enclose the human body – and therefore is able to limit anxiety in people suffering from claustrophobia.
Diagnostic X-ray imaging of the human skeleton is commonly used to ascertain whether any bones are damaged or broken. Also, in dentistry, X-rays are useful for determining whether treatment is required as well as evaluating the health of the teeth. In general, X-rays have been used to guide surgeons through operational procedures; for example, in the detection of bone tumours.
What is a CT scan?
In some cases, the patient requires a computed tomography scan known as a CT scan. The CT scanner is able to create an internal image of the human body by using a combination of X-rays and computers. Ultimately, the CT scanner is an advanced X-ray machine that can produce 3-D images of soft tissue inside the body. This is in contrast to planer X-ray machines which only generate 2-D images and can be used to detect pneumonia and certain cancers.
Furthermore, the CT scanner is capable of imaging several parts of the human body which include the skeleton, internal organs and blood vessels. Moreover, CT scanning is mostly used for the brain, neck, spine and chest. Another important use of the CT scanner is to locate tumours and broken bones within the patient.
However, an X-ray scan is sometimes not conclusive and therefore the CT scanner is used to aid further diagnosis. The CT scanning process involves the patient resting on a movable horizontal bed, which travels through the entrance of the scanner, with the gantry containing the X-ray units rotating around cross-sections of the body. At this stage, the patient is advised to remain still in order to obtain clear CT images.
During the scanning procedure, the radiologist will be in an adjoining room to operate the scanner and be shielded from the radiation. The CT scan can take up to 20 minutes – depending on the condition of the patient – and the scans are subsequently analysed by a computer. Also, CT scanning is a non-invasive, pain-free technique.
What is an MRI scan?
Magnetic resonance imaging, known as an MRI scan is a technique to produce cross-sectional images of the human body. Both CT and MRI produce high-quality images which enable healthcare professionals to evaluate the disease state in the patient.
MRI is used to scan the brain and spinal cord; for example, in multiple sclerosis (MS) patients and other neurological conditions. The MRI scanner is also used for the skeleton, the heart and blood vessels and internal organs. The MRI scanner surrounds the whole body, which is in contrast to the CT scanner. The process involves the patient lying on a movable bed which slowly transports into a ‘cylinder,’ with a patient-friendly entry diameter of at least 60 cm.
The patient will then be subjected to a strong magnetic field and a sequence of radio waves to create the images. While the patient is in the MRI scanner, the radiographer will be in an adjacent viewing room and in contact with the patient. The MRI scan can take up to 90 minutes and is a much noisier machine than the CT scanner. Hence, the patient will be given ear protection.
There are several advantages of having an MRI scan – as opposed to a CT scan – primarily because X-ray radiation is not involved. Therefore, it remains a safe procedure that is suitable for use on pregnant women. Since MRI uses strong magnetic fields, it is essential for the patient to notify healthcare professionals about shunts, pacemakers and any metal objects within the body.
In some cases, patients will be offered an open MRI scanning procedure instead of a closed system. These open scanners will still provide high-quality imaging but are not suitable for cardiac and breast imaging. The main benefit of the open MRI scanner is for patients who experience anxiety or claustrophobia. The patient in the open MRI scanner will be more comfortable and relaxed and able to remain still allowing the radiographer to obtain high-quality scans.
What is a PET scan?
Positron emission tomography, known as a PET scan, is used to create 3-D images of the human body. They are mostly located in the Nuclear Medicine Departments of hospitals and healthcare providers. The PET scanner can be combined with CT to produce images about the internal workings of the body.
A whole-body PET scan is used on cancer patients to detect the progression of the disease and to evaluate the patient response to chemotherapy and radiotherapy treatment. These PET scans are also used in the planning of certain types of surgery; for example, brain or heart operations. Furthermore, PET imaging can be used to help in the diagnosis of dementia by evaluating brain function.
When a patient is offered a PET scan, they will be injected with a radiotracer. The majority of patients will receive a radiotracer called FDG (18F-fluorodeoxyglucose), which is injected into the arm, emitting radiation over a specific time frame.
The radiation emitted is detected by the PET scanner: this creates the images and will also indicate the level of radiation accumulating inside the body. Accordingly, if no FDG levels are indicated that would specify normal body function within that particular region of the body.FDG is similar to glucose and the cancer cells will take this radiotracer up at a faster rate than normal cells.
Therefore, by analysing the PET scans for FDG accumulation, the type of cancer can be identified and tracked throughout the human body. A typical PET scan can take up to 30 minutes to complete. Furthermore, the PET scanner can be used to investigate metabolic changes at the cellular level in various organs or tissues. This would be more of a challenge with CT or MRI scanners.
What is an ultrasound scan?
An ultrasound scanner produces images by passing high-frequency waves into the human body. Ultrasound is widely used to obtain images of unborn children, in real-time. They are also used by surgeons – for specific procedures – to help them in the diagnosis of the patient. Ultrasound systems work by using a probe, which is capable of emitting high-frequency sound waves. The sound waves reflect off various organs and surrounding tissues to create echoes, which bounce back to the probe to form 2-D or 3-D images, in real-time. The scanning process can last up to 45 minutes and is performed both externally and internally.
Accordingly, endoscopic ultrasound (EUS), is an invasive procedure to investigate gastrointestinal and lung diseases. The EUS imaging technique can be used to find the causes of abdominal or chest pain. EUS can be used in conjunction with other diagnostic tests such as CT and MRI scans to evaluate cancers of the colon, oesophagus, lung, pancreas, stomach and rectum. The main advantage of ultrasound is that there are no patient after-effects and normal activities can be resumed. Also, the results of the ultrasound scan can be evaluated in real-time and there is no need for the patient to wait.
