|Imaging (X-rays, CT scans, ultrasound, PET, MRI, mammograms)|
|Since the late 1890's X-rays have been used for
diagnostic imaging. Improvements in conventional diagnostic X-rays
include capturing the image digitally rather than on film (e.g. digital
mammography). Using computers to combine information from multiple X-ray
pictures and produce three dimensional views of the body (CT scans) was
an obvious major advance, followed by MRI which accomplishes the same
thing with magnets. Ultrasound is another effective imaging technique.
In nuclear medicine a specific chemical is injected into the patient
that will localize in specific parts of the body or cancer and them emit
radiation. PET scans are the best example of this.
imaging is probably the best example of how all these diagnostic
modalities can be used in combination to thoroughly evaluate a patient.
Some of the most common techniques are noted below
Medical sonography (ultrasonography) is an ultrasound-based diagnostic imaging technique used to visualize muscles and internal organs, their size, structures and possible pathologies or lesions. Obstetric sonography is commonly used during pregnancy and is widely recognized by the public. There are a plethora of diagnostic and therapeutic applications practiced in medicine. In physics the term "ultrasound" applies to all acoustic energy with a frequency above human hearing (20,000 hertz or 20 kilohertz). Typical diagnostic sonographic scanners operate in the frequency range of 2 to 18 megahertz, hundreds of times greater than the limit of human hearing. The choice of frequency is a trade-off between spatial resolution of the image and imaging depth: lower frequencies produce less resolution but image deeper into the body.
Computed tomography is a medical imaging method employing tomography where digital geometry processing is used to generate a three-dimensional image of the internals of an object from a large series of two-dimensional X-ray images taken around a single axis of rotation. The word "tomography" is derived from the Greek tomos (slice) and graphein (to write). CT produces a volume of data which can be manipulated, through a process known as windowing, in order to demonstrate various structures based on their ability to block the X-ray beam. Although historically the images generated were in the axial or transverse plane (orthogonal to the long axis of the body), modern scanners allow this volume of data to be reformatted in various planes or even as volumetric (3D) representations of structures.
Magnetic resonance imaging (MRI) is primarily used in medical imaging to visualize the structure and function of the body. It provides detailed images of the body in any plane. MR has much greater soft tissue contrast than Computed tomography (CT) making it especially useful in neurological, musculoskeletal, cardiovascular and oncological diseases. Unlike CT it uses no ionizing radiation. The scanner creates a powerful magnetic field which aligns the magnetization of hydrogen atoms in the body. Radio waves are used to alter the alignment of this magnetization. This causes the hydrogen atoms to emit a weak radio signal which is amplified by the scanner. This signal can be manipulated by additional magnetic fields to build up enough information to reconstruct an image of the body.
Positron emission tomography (PET) is a nuclear medicine medical
imaging technique which produces a three-dimensional image or map of
functional processes in the body. The system detects pairs of gamma rays
emitted indirectly by a positron-emitting radioisotope, which is
introduced into the body on a metabolically active molecule. Images of
metabolic activity in space are then reconstructed by computer analysis,
often in modern scanners aided by results from a CT X-ray scan performed
on the patient at the same time, in the same machine.