Medical Imaging Modalities use MRI, PET, SPECT, CT and X-Ray equipment including diagnostic imaging agents

Medical Imaging Modalities | X-Rays and Medical Radiation

Medical Imaging Modalities involves several scanning techniques to visualise the human body for diagnostic and treatment purposes. Also, these modalities are very useful for patient follow-up, with regards to the progress of the disease state, which has already been diagnosed, and/or is undergoing a treatment plan.  The vast majority of imaging is based on the application of X-rays and ultrasound (US).  These medical imaging modalities are involved in all levels of hospital care. In addition, they are instrumental in the public health and preventive medicine settings as well as in the curative and further extending to palliative care. The main objective is to establish the correct diagnoses.

Medical Radiation

Medical imaging in a clinical setting is a vital contribution to the overall diagnosis of the patient and helps in the decision of an overall treatment plan. The utilisation of imaging techniques in medical radiation is increasing with new technological advances in medical sciences. Therefore, in the spectrum of a broad range of imaging modalities are the specialities of nuclear medicine, positron emission tomography (PET), magnetic resonance imaging (MRI) and ultrasound. Overall, imaging for medical radiation purposes involves a team of radiologists, radiographers, sonographers and medical physicists.

Positron emission tomography (PET) uses medical radiation a gamma camera to evaluate organ and tissue functions with the body

Stages of PET Scanning

(Patching SG. Journal of Diagnostic Imaging in Therapy. 2015; 2(1): 30-102. CrossRef)

Medical imaging involves a multidisciplinary approach to obtain a correct diagnosis for the individual patient with an aim of providing a personalised approach to patient care. These imaging techniques can be applied as non-invasive methods to view inside the human body, without any surgical intervention. They can be used to assist diagnosis or treat a variety of medical conditions. Medical imaging techniques utilise radiation that is part of the electromagnetic spectrum. These include imaging X-rays which are the conventional X-ray, computed tomography (CT) and mammography. To improve X-ray image quality, a contrast agent can be used, for example, in angiography examinations.

Radiography utilise medical radiation in the form of conventional X-ray, computed tomography (CT) and mammography


Medical Imaging Modalities

Furthermore, imaging utilised in nuclear medicine can be attributed to several techniques to visualise biological processes. The radiopharmaceuticals used are usually small amounts of radioactive markers: these are used in molecular imaging. Other non-radioactive types of imaging include magnetic resonance imaging (MRI) and ultrasound (US) imaging. MRI uses strong magnetic fields, which do not produce any known irreversible biological effects in humans. Diagnostic ultrasound (US) systems use high-frequency sound waves to produce images of internal body organs and soft tissue. X-ray imaging uses X-ray beams that are projected onto the body. When these X-ray beams pass through the human body some are absorbed, and the resultant image is detected on the other side of the body.

Angiography is a medical procedure that uses a dye in the arteries to enable x-rays to locate the blood vessels


Some types of medical imaging function without using ionising radiation; for example, magnetic resonance imaging (MRI) and ultrasound imaging and these have significant applications in the diagnosis of disease. Medical imaging modalities include positron emission tomography (PET), single photon emission computed tomography (SPECT) and hybrid imaging systems. Alternatively, other systems use the application of radio-guided surgery (RGS) and this extends to positron emission mammography (PEM). In addition, there is the application of short and long-lived radioisotopes for research and development of new imaging agents and associated targeted therapies. Other techniques include magnetic resonance imaging (MRI), computed tomography (CT), ultrasound (US) imaging and planar X-ray (digital, analogue and portable) systems.

The special resolution required to elucidate detailed images of various structures within the human body are the main practical limitations of current imaging modalities. However, the rate of image acquisitions has increased over the last decade; this does not allow for the sensitivity required in order to express anatomical structure and function which is limited by the radiation dose amongst other factors.

Spatial Resolution of Imaging Modalities and Medical Radiation

Imaging Modality Spatial Resolution (mm)
Animal Clinical
PET 1-2 6-10
SPECT 0.5-2 7-15
OPTICAL 2-5 (Visible to IR)
MRI 0.025-0.1 0.2
US 0.05-0.5 0.1-1
CT 0.03-0.4 0.5-1

Medical radiation imaging technologies will not be dictated by the advancements in imaging quality, but more likely the objective will be to reduce the cost and scanning time including exposure to radiation. These technical innovations allow for the rational conclusion that medical radiation dose, scanning speed, image resolution and sensitivity including cost per patient will all be elements of personalised medicine in the future.

Consequently, the medical physicist will play a pivotal role to further these challenges: especially to extend knowledge and understanding of the effect of which signals used to construct 3-D time-dependent images.

In particular, it is important to account for the physical and biological factors that modulate the behaviour of different energy forms within the human body. Moreover, to understand how to interpret images and derive more crucial information regarding the patient’s disease state in order to formulate a treatment plan which is personal to the patient.

As with the continual development and improvements in imaging, it is essential to understand the specific biological episode associated with each specific disease state. It would be crucial to design medical imaging systems that can recognise a ‘fingerprint’ that can be attributed to an individual disease.

Furthermore, new imaging modalities would be used to evaluate changes in tissue composition resulting from a disease like fibrosis. In this case, the physiological parameter would be the reduction of blood flow in arteries. Other techniques could evaluate the change in conductivity or magnetic susceptibility of brain tissue. All of these improvements could help in the understanding of the contrast mechanisms in several medical imaging modalities.

In essence, it is important to make use of the data within digital images to develop more quantitative tissue characterisation from these anatomical scans. For example, functional magnetic resonance imaging (fMRI) has transformed understanding the construction of the brain.

This imaging technique has provided the exact relationship between the MRI signals used to map neural activity. However, the fundamental neurochemical and electrophysiological processes are not well defined.

Diagnostic imaging tools provide powerful techniques to locate biological processes within the human body. This includes spatial heterogeneity and related changes to the different regions within the fine detail surrounding the anatomical structure.

Advancements in medical imaging will contribute to an overall personalised treatment plan for each patient. This can only be guaranteed by continuing translational research in the design of novel radiopharmaceuticals and biomarkers in order to increase the efforts to devise robust personalised treatment plans for individual patients.

All the above imaging modalities are discussed in the Journal of Diagnostic Imaging in Therapy according to the aims and scope.

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