Frequently Asked Questions

Computed Tomography (CT) (11)
What is Computed Tomography (CT)?

"Computed tomography (formerly known as computerized axial tomography or CAT scan) measures the weakening, or attenuation, of x-ray beams as they pass through sections of an object from hundreds of different angles. From the evidence of these measurements, a computer is able to reconstruct two and three dimensional images of the objects interior." (Eisenberg, 1992)

1992 Eisenberg, E. L. Radiology. An Illustrated History, A. S. Patterson (ed.), Mosby Year Book, pp. 467-468.

"The relationship between the CT number of a structure and its physical density is defined by the equation Q = CT + 1000 (Q in mg/cm3, CT in HU (Hounsfield Units)). This equation holds true as long as the effective atomic number of the substance (i.e. its atomic composition) in the displayed voxel is similar to that of water. This applies with reasonable accuracy to fluids, soft tissues, and less to fat but not to iodinated contrast media of calcified structures. For this reason, the CT number of a soft-tissue structure is often used interchangeably with "density"." (Prokop and Galanski, 2003)

2003 Prokop, M., and M. Galanski. Spiral and Multislice Computed Tomography of the Body, A. J. van der Molen, and C. M. Schaefer-Prokop (eds.), Thieme, New York, pp. 1-1090.

"Hounsfield units are a unit of measure that represents the different density levels of tissues and or other substances. The density of pure water was arbitrarily set at 0 HU and that of air at -1000 HU." (Hofer, 2000)

2000 Hoffer, M. CT Teaching Manual, Georg Thieme Verlag, pp.12-13.

"A CT image is composed of a square image matrix that ranges in size from 256 X 256 to 1024 X 1024 picture elements or pixels. Since a CT section has a finite thickness, each pixel actually represents a small volume element, or voxel. The size of this voxel depends on the matrix size, the selected field of view (FOV), and the section thickness." (Prokop and Galanski, 2003)

2003 Prokop, M., and M. Galanski. Spiral and Multislice Computed Tomography of the Body, A. J. van der Molen, and C. M. Schaefer-Prokop (eds.), Thieme, New York, pp. 1-1090.

"Abbreviation for Digital Imaging and Communications in Medicine, a joint standard of the American College of Radiology and National Equipment Manufacturers Association; specifies entities (or objects) and functions (or services) to allow communication between various image sources and other computer devices, such as archives or workstations." (PDR, Pugh et al. (eds.), 2000)

2000 Physicians Desktop Reference (PDR) Medical Dictionary, N.B. Pugh, B. Werner, T. W. Filardo, P. W. Binns, L. G. Francis, R. Lukens, B. Montgomery, B. L. Ferretti, K. J. Cradle, D. Workman (eds.), Lippincott Williams & Wilkens, Second Edition, pp. 1-2098.

A micron is a unit of measurement equal to one millionth of one meter.

"In position, not extending beyond the focus or level of origin." (PDR, Pugh et al. (eds.), 2000)

2000 Physicians Desktop Reference (PDR) Medical Dictionary, N.B. Pugh, B. Werner, T. W. Filardo, P. W. Binns, L. G. Francis, R. Lukens, B. Montgomery, B. L. Ferretti, K. J. Cradle, D. Workman (eds.), Lippincott Williams & Wilkens, Second Edition, pp. 1-2098.

"A shaded surface display (SSD) is a surface-rendered image that provides a realistically looking three-dimensional view of the surface of a structure of interest within the acquired volume set." (Prokop and Galanski, 2003)

2003 Prokop, M., and M. Galanski. Spiral and Multislice Computed Tomography of the Body, A. J. van der Molen, and C. M. Schaefer-Prokop (eds.), Thieme, New York, pp. 1-1090.

"Maximum intensity projection (MIP) and minimum intensity projection (MinIP) are volume-rendering techniques in which suitable editing methods are used to define the volume of interest (VOI). All of the CT image data set may be used, or the volume may be confined to a region of interest (ROI). In the most difficult case, only selected organ systems are included or excluded from VOI. The actual images are generated by projecting the volume of interest into a viewing plane and displaying the maximum CT numbers (for MIP) or the minimum CT numbers (for MinIP) that are encountered along the direction of the projection, called the viewing angle. Both techniques ensure that optimum contrast is produced between small, high-contrast structures and surrounding tissues." (Prokop and Galanski, 2003)

2003 Prokop, M., and M. Galanski. Spiral and Multislice Computed Tomography of the Body, A. J. van der Molen, and C. M. Schaefer-Prokop (eds.), Thieme, New York, pp. 1-1090.

"Multiplanar reformations (MPR's) are two-dimensional reformatted images that are reconstructed secondarily in arbitrary planes from the stack of axial image data." (Prokop and Galanski, 2003)

2003 Prokop, M., and M. Galanski. Spiral and Multislice Computed Tomography of the Body, A. J. van der Molen, and C. M. Schaefer-Prokop (eds.), Thieme, New York, pp. 1-1090.

"VRT assigns a range of opacity values to CT numbers and thus yields a better definition of object contours or semitransparent display of structures." (Prokop and Galanski, 2003)

2003 Prokop, M., and M. Galanski. Spiral and Multislice Computed Tomography of the Body, A. J. van der Molen, and C. M. Schaefer-Prokop (eds.), Thieme, New York, pp. 1-1090.

Marine Research Facility (2)

A necropsy is an autopsy performed on an animal.

CSI or the Computerized Scanning and Imaging Facility which is housed in the WHOI Marine Research Facility (MRF), is a research dedicated medical imaging facility that uses the technology of Computed Tomography to study hearing in both marine and land animal taxa.

Woods Hole Oceanographic Institution (5)

Because WHOI operates year-round, its needs do not necessarily increase in the summer months. If interested in a job, please browse WHOI's list of current job openings. If you are interested in a summer position, you should monitor this page regularly to see if a job has been posted, and follow the same procedures as you would for all of our job openings.

Although Alvin is operated by WHOI, the manned submersible is rarely in port here. Usually Alvin is at sea with the research vessel Atlantis, bringing researchers and scientists to the ocean depths.
» Find out where Alvin and Atlantis are now

At our Ocean Science Exhibit Center you can sit inside a full-scale model of the Alvin personnel sphere, look through its viewports to see footage from the sea floor, and learn more about how Alvin is built to withstand the pressures of the deep. Located at 15 School Street. Suggested donation: $2/person aged 10 and over; under 10, free. Small gift shop. Telephone (508) 289-2663 or 289-2252.

WHOI education programs operate primarily on the graduate level. A joint program with the Massachusetts Institute of Technology (MIT) enrolls students working toward masters and doctoral degrees. Some summer student fellowships and minority traineeships are awarded to undergraduates and recent college graduates. More information about WHOI's educational programs

There are lots of resources available that will put you on the right track toward becoming a marine biologist and any other marine-related career. The guidance and career counselors at your high school or college are a great resource or check out the WHOI marine careers page

You can call WHOI’s Information Office with general questions about marine science and on-going research at WHOI.
Email: information [at] whoi [dot] edu (information [at] whoi [dot] edu)
Telephone: +1 (508) 289-2252.

The Information Office provides packets of general information about WHOI and on specific oceanographic subjects, answers basic questions, and, where ever possible, directs people to other resources both within the Institution and in other organizations or agencies. You can also check out the WHOI K-12 resource page