Biomedical Engineering Reference
In-Depth Information
Right hemisphere
Left hemisphere
N1
N1
N1
Anterior
N1
HG
HG
PT
STG
STG
Location change
N1
Z
2
2
100 ms
2nd sound (“Probe”)
Attend location
400 ms
Attend phoneme
Phoneme change
FIGURE 16.54 (Top) MEG locations of equivalent-current dipoles (ECD) sources to two different words,
“Adaptor” and “Probe,” sequentially spoken from different external spatial locations, displayed on the inflated
brain hemispheres, MRI images, of one subject. (Middle and bottom) Amplitude-normalized source waveforms
in the middle indicate that the “where” pathways are associated with the N1 locations, whereas waveforms at
the bottom for parallel “what” pathways are connected with the N1 locations. Differences (peak changes encircled)
in the averaged waveforms indicate the effects of selective attention to either sound or location. The N1 response
amplitudes to Probes (encircled) are modulated task-dependently. The posterior N1 activity to Probes following
spatially different Adaptors is enhanced by spatial attention. The anterior N1 activity to Probes following phoneti-
cally different Adaptors is enhanced by phonetic attention.
From [1].
16.5.1 Computed Tomography Agents
Intravenously administered CT contrast agents containing iodine or gadolinium are
employed in the visualization of blood vessels. For example, for a CT pulmonary angio-
gram, emboli and obstructions can be seen through attenuation of the x-rays or opacifica-
tion, which brightens the appearance of flow in a vessel. Through the enhancement of
blood vessels, other applications include visualization of the internal structures of the brain,
spine, liver, and kidney and other organs. Afterward, the kidney and liver normally aid in
passing the agents out of the system. In some cases, these agents may involve some risk and
possible allergic reactions such as those of the kidney.
For the diagnosis of abdominal diseases and injuries, CT contrast agents are adminis-
tered either orally or rectally. A dilute suspension of barium sulfate is used most often.
Applications include the diagnosis and characterization of cancer and the investigation of
sources of severe abdominal pain and trauma.
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