Medical Imaging Lecture 1

What is Medical Imaging?? Medical imaging refers to a number of techniques that can be used as non-invasive methods of looking inside the body. This means the body does not have to be opened up surgically for medical practitioners to look at various organs and areas. It can be used to assist diagnosis or treatment of different medical conditions. Imaging techniques use radiations that form part of the electromagnetic spectrum. It's easy to forget that visible light (that is the colours that we as humans can see) forms only a fraction of the electromagnetic spectrum.

Why is medical imaging important? In an ideal world we would be able to diagnose, treat and cure patients without causing any harmful side effects. The use of medical imaging has enabled doctors to see inside a patient without having to cut them open. Medical imaging also helps us learn more about neurobiology and human behaviors. Medical imaging brings scientists from biology, chemistry and physics together and the technologies developed can often be used in many disciplines.

Benefits of Medical Imaging Health Benefit : Medical imaging helps you detect and diagnose disease at its earliest, most treatable stages and guides physicians and patients in determining the most appropriate and effective care. Health Care Costs & Quality: By catching disease early, reducing the need for invasive, in-patient procedures and facilitating shorter recovery times, medical imaging saves money and improves efficiency in the health care system. Technology & Innovation: Radiation therapy and medical imaging technologies have revolutionized health care delivery in America and around the world. Extending human vision into the very nature of disease, medical imaging enables a new and more powerful generation of diagnosis and intervention. Radiation therapy offers highly personalized and targeted means of killing cancer cells while leaving healthy ones untouched. Jobs & the Economy: Medical imaging and radiation therapy is the source of hundreds of thousands of jobs all over the world.

Medical Diagnosis Determination of the identity of a possible disease or disorder.

Medical imaging modalities Radiography Computed Tomography Magnetic Resonance Imaging Ultrasonography Nuclear Medicine Endoscopy Thermography

History of Medical Imaging

Radiology & Diagnostic Imaging Overview Radiology Study of the diagnostic and therapeutic uses of x-rays Radiology uses imaging to diagnose and treat diseases seen within the body. Radiologists use a variety of imaging techniques such as X ray radiography, ultrasound, computed tomography (CT), nuclear medicine including positron emission tomography (PET), and magnetic resonance imaging (MRI) to diagnose and/or treat diseases. Radiography Medical radiography is a broad term that covers several types of studies that require the visualization of the internal parts of the body using x-ray techniques. During a radiographic procedure, an x-ray beam is passed through the body. A portion of the x-rays are absorbed or scattered by the internal structure and the remaining x-ray pattern is transmitted to a detector so that an image may be recorded for later evaluation. The recoding of the pattern may occur on film or through electronic means.

Radiology & Diagnostic Imaging Overview X-Rays: X-rays are a form of electromagnetic radiation, similar to visible light. Unlike light, however, x-rays have higher energy and can pass through most objects, including the body. Medical x-rays are used to generate images of tissues and structures inside the body. If x-rays travelling through the body also pass through an x-ray detector on the other side of the patient, an image will be formed that represents the “shadows” formed by the objects inside the body.

Electromagnetic spectrum

11 X-rays Electrons emitted from a heated cathode, bombard the anode: Characteristic X-rays: The free electron collides with an atom in the anode, knocking an electron out of a lower orbital. A higher orbital electron fills the empty position, releasing its excess energy as a photon. Bremsstrahlung: Does not depend on target material. Continuous spectrum. The free electron is attracted to the atom nucleus in the anode. As the electron speeds past, the nucleus alters its course. The electron loses energy, which it releases as an X-ray photon.

How do medical x-rays work? To create a radiograph, a patient is positioned so that the part of the body being imaged is located between an x-ray source and an x-ray detector. When the machine is turned on, x-rays travel through the body and are absorbed in different amounts by different tissues, depending on the radiological density of the tissues they pass through. Radiological density is determined by both the density and the atomic number of the materials being imaged. For example, structures such as bone contain calcium, which has a higher atomic number than most tissues. Because of this property, bones readily absorb x-rays and, thus, produce high contrast on the x-ray detector. As a result, bony structures appear whiter than other tissues against the black background of a radiograph. Conversely, x-rays travel more easily through less radiologically dense tissues such as fat and muscle, as well as through air-filled cavities such as the lungs. These structures are displayed in shades of gray on a radiograph.

How do medical x-rays work?

X-Ray system

Benefits Medical x-rays have increased our ability to detect disease or injury early enough for a medical problem to be managed, treated, or cured. When performed appropriately and early enough, these procedures can improve health and may even save a person’s life.

Are there risks? The most significant risks are: A small increase in the possibility that a person exposed to x-rays will develop cancer later in life The possibility of cataracts and skin burns, but only at extremely high levels of radiation exposure

The risk of developing cancer from radiation exposure is generally small, and it depends on at least three factors—the amount of radiation dose, the age at exposure, and the sex of the person exposed: The lifetime risk of cancer increases the larger the dose per exam (including re-takes) and the more x-ray exams a patient undergoes. The lifetime risk of cancer is larger for a patient who received x- rays at a younger age than for one who receives them at an older age. Women are at a somewhat higher lifetime risk than men for developing radiation-associated cancer after receiving the same exposures at the same ages. Children have a longer life expectancy and, thus, have a higher relative risk for developing cancer than adults. Risk of Cancer from X-rays

Reduction of radiation risks Keeping a “medical x-ray history” with the names of your radiological exams or procedures, the dates and places where you had them, and the physicians who referred you for those exams Making your current healthcare providers aware of your medical x- ray history; Asking your healthcare provider about whether or not alternatives to x-ray exams would allow the provider to make a good assessment or provide appropriate treatment for your medical situation Providing interpreting physicians and referring physicians with recent x-ray images and radiology reports Informing radiologists or x-ray technologists in advance if you are pregnant or think you may be pregnant.

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