Radiology
Radiology is the medical
specialty that uses medical imaging to diagnose and treat
diseases within the human body.
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) are
used to diagnose or treat diseases. Interventional radiology is the
performance of usually minimally invasive medical
procedures with the guidance of imaging technologies such as those mentioned
above.
Computed
tomography
CT imaging uses X-rays in
conjunction with computing algorithms to
image the body. In CT, an X-ray tube opposite an X-ray detector (or
detectors) in a ring-shaped apparatus rotate around a patient, producing a
computer-generated cross-sectional image (tomogram). CT is acquired in
the axial plane, with coronal and sagittal
images produced by computer reconstruction. Radiocontrast agents are often used
with CT for enhanced delineation of anatomy. Although radiographs provide
higher spatial resolution, CT can detect more subtle variations in attenuation
of X-rays (higher contrast resolution). CT exposes the patient to significantly
more ionizing radiation than a radiograph.
Ultrasound
Medical ultrasonography uses
ultrasound (high-frequency sound waves) to visualize soft tissue structures in
the body in real time. No ionizing radiation is involved, but the
quality of the images obtained using ultrasound is highly dependent on the
skill of the person (ultrasonographer) performing the exam and the patient's
body size. Examinations of larger, overweight patients
may have a decrease in image quality as their subcutaneous
fat absorbs more of the sound waves. This results in fewer
sound waves penetrating to organs and reflecting back to the transducer,
resulting in loss of information and a poorer quality image. Ultrasound is also
limited by its inability to image through air pockets (lungs, bowel loops) or
bone. Its use in medical imaging has developed mostly within the last 30 years.
The first ultrasound images were static and two-dimensional (2D), but with
modern ultrasonography, 3D reconstructions can be observed in real time,
effectively becoming "4D".
