| Patients have the following procedures to | | | | the legs can be found via ultrasound before |
| provide images for Radiological decisions to | | | | it dislodges and travels to the brain |
| be made. | | | | (creating a stroke), heart (creating coronary |
| | | | blockage), or lungs (pulmonary embolism), all |
| Projection radiography | | | | of which are fatal if left untreated. |
| | | | Ultrasound is useful for image-guided |
| Radiographs (or Roentgenographs, named after | | | | interventions like biopsies and drainages |
| the discoverer of X-rays, Wilhelm Conrad | | | | such as thoracentesis). It is also used in |
| Roentgen (1845-1923)) are often used for | | | | the treatment of kidney stones (renal |
| evaluation of bony structures and soft | | | | lithiasis) via lithotripsy. Small portable |
| tissues. An X-Ray machine directs | | | | ultrasound devices now replace peritoneal |
| electromagnetic radiation upon a specified | | | | lavage in the triage of trauma victims by |
| region in the body. This radiation tends to | | | | directly assessing for the presence of |
| pass through less dense objects (skin, fat, | | | | hemorrhage in the peritoneum and the |
| muscle, and other tissues), but is absorbed | | | | integrity of the major viscera including the |
| by denser materials (bones, tumors, lungs | | | | liver, spleen and kidneys. Extensive |
| affected by severe pneumonia). Radiation | | | | hemoperitoneum (bleeding inside the body |
| which has passed through a patient then | | | | cavity) or injury to the major organs may |
| exposes an x-ray film. Areas of film exposed | | | | require emergent surgical exploration and |
| to higher amounts of radiation will appear | | | | repair. |
| black or dark gray after development. The | | | | |
| unexposed areas of film remain white. | | | | MRI/NMR |
| | | | |
| Fluoroscopy | | | | MR image of human kneeMRI uses strong |
| | | | magnetic fields to align spinning atomic |
| Fluoroscopy and angiography are special | | | | nuclei (usually hydrogen protons) within body |
| applications of X-ray imaging, where a | | | | tissues, then uses a radio signal to disturb |
| fluorescent screen or image intensifier tube | | | | the axis of rotation of these nuclei and |
| is connected to a closed-circuit television | | | | observes the radio frequency signal generated |
| system, which allows real-time imaging of | | | | as the nuclei return to their baseline |
| structures in motion or augmented with a | | | | states. MRI scans give the best soft tissue |
| radiocontrast agent. Radiocontrast agents are | | | | contrast of all the imaging modalities. With |
| administered, often swallowed or injected | | | | advances in scanning speed and spatial |
| into the body of the patient, to help | | | | resolution, and improvements in computer 3D |
| delineate anatomy such as the blood vessels, | | | | algorithms and hardware, MRI has great |
| the genitourinary system or the | | | | potential for development in the next few |
| gastrointestinal tract. Specific | | | | years. One disadvantage is that the patient |
| radiocontrast agents are used for specific | | | | has to hold still for long periods of time in |
| types of evaluations; for example, barium in | | | | a noisy, cramped space while the imaging is |
| a suspension is administered into the | | | | performed. Recent improvements in magnet |
| gastrointestinal tract and imaged with | | | | design like wider, shorter magnet bores and |
| fluoroscopy or radiography. Radiocontrast | | | | more open magnet designs, have brought some |
| agents, which strongly absorb X-ray | | | | relief for claustrophobic patients. MRI has |
| radiation, in conjunction with the real-time | | | | great benefit in imaging the brain,spine, and |
| imaging allows demonstration of dynamic | | | | musculoskeletal system. The modality can be |
| processes, such as peristalsis in the | | | | contraindicated for patients with pacemakers, |
| digestive tract or blood flow in arteries and | | | | certain types of cerebral aneurysmal clips or |
| veins. | | | | metallic hardware due to the strong magnetic |
| | | | fields. Areas of potential advancement |
| CT scanning | | | | include functional imaging, cardiovascular |
| | | | MRI, as well as MR image guided therapy. |
| CT imaging uses X-rays in conjunction with | | | | |
| computing algorithms to image a variety of | | | | Nuclear medicine |
| soft tissues in the body. CT is acquired in | | | | |
| the axial plane, while coronal and sagittal | | | | Nuclear medicine imaging involves the |
| images can be rendered by computer | | | | administration into the patient of substances |
| reconstruction. Radiocontrast agents are | | | | labelled with radioactive tracers which have |
| often used with CT for enhanced delineation | | | | affinity for particular tissues. The heart, |
| of anatomy. Intravenous contrast allows 3D | | | | lungs, thyroid, liver, gallbladder, and bones |
| reconstructions of arteries and veins. | | | | are commonly evaluated for particular |
| Although radiographs provide higher | | | | conditions using these techniques. While |
| resolution for bone X-rays, CT can generate | | | | anatomical detail is limited in these |
| much more detailed images of the soft | | | | studies, nuclear medicine is useful in |
| tissues. CT exposes the patient to more | | | | displaying physiological function. As such, |
| ionizing radiation than a radiograph. | | | | processes such as the growth of a tumor can |
| | | | often be monitored, even when the tumor |
| Ultrasound | | | | cannot be adequately visualized using any of |
| | | | the other modalities. The principal imaging |
| Medical ultrasonography uses ultrasound | | | | device is the gamma camera which detects the |
| (high-frequency sound waves) to visualize | | | | radiation emitted by the tracer in the body |
| soft tissue structures in the body in real | | | | and displays it as an image. Often the |
| time. No ionizing radiation is involved, but | | | | information is converted into a series of |
| the quality of the images obtained using | | | | slices through the body. In the most modern |
| ultrasound is highly dependent on the skill | | | | devices Nuclear Medicine images can be fused |
| of the person (ultrasonographer) performing | | | | with a CT scan taken quasi-simultaneously so |
| the exam. The use of ultrasound in medical | | | | that the physiological information can be |
| imaging has developed mostly within the last | | | | overlayed on co-registered with the |
| 30 years. The first ultrasound images were | | | | anatomical structures to improve diagnostic |
| static and two dimensional (2D), but with | | | | accuracy. |
| modern-day ultrasonography 3D reconstructions | | | | |
| can be observed in real-time; effectively | | | | PET scanning also falls under "nuclear |
| becoming 4D. | | | | medicine." |
| | | | |
| Because ultrasound does not utilize ionizing | | | | The applications of nuclear medicine can |
| radiation, unlike radiography, CT scans, and | | | | include bone scanning which traditionally has |
| nuclear medicine imaging techniques, it is | | | | had a strong role in the work-up/staging of |
| generally considered safer. For this reason, | | | | cancers. Myocardial perfusion imaging is a |
| this modality plays a vital role in | | | | sensitive and specific screening exam for |
| obstetrical imaging. Fetal development can be | | | | reversible myocardial ischemia, which when |
| thoroughly evalauted allowing early diagnosis | | | | present requires angiographic confirmation |
| of fetal anomalies or confirmation of a | | | | and potentially life-saving balloon |
| normal gestation. Color flow Doppler well | | | | angioplasty, stenting or cardiac bypass |
| documents the severity of peripheral vascular | | | | grafting. Molecular Imaging is the new and |
| disease. Stenosis of the carotid arteries can | | | | exciting frontier in this field. |
| herald cerebral infarcts (strokes). A DVT in | | | | |