To be included in this study, the animal must have demonstrated:
minimal eye movement during the MRI examination, nongasping respiratory
pattern before the MRI examination, rectal temperatures in the range
36.5°C to 38.5°C, and PaO
2 > 350 mm Hg and
PaCO
2 between 45 and 65 mm Hg during the carbogen
challenge. The number of animals examined by MRI that satisfied the
inclusion criterion for the 3.5-month control, 3.5-month galactosemia,
15- to 18-month control, and 15- to 18-month galactosemia groups were,
respectively, 7, 10, 3, and 4. The MRI data from these animals were
transferred to a Macintosh IIcx computer. Image registration was
performed using software written inhouse for the program IMAGE (a
freeware program available at http://rsb.info.nih.gov/nih-image/).
After registration, the room air images were averaged to improve the
signal–to–noise ratio. All pixel signal intensities in the average
room air image and the 2-minute carbogen image were then normalized to
the external standard intensity. On a pixel-by-pixel basis, signal
intensity changes during carbogen breathing were calculated, converted
to ΔP
o 2 values, and displayed as a
pseudocolor parameter map as previously described.
7 Data
along a 1-pixel-thick line (200 μm) drawn in the preretinal vitreous
space were extracted and displayed as a preretinal vitreousΔ
P
o 2 band. Each band represents ora
serrata–to–ora serrata ΔP
o 2 values over a 1-mm-thick section of retina (the MRI slice thickness).
The width of the bands is arbitrary. The longer white tick mark in the
center of each band represents the posterior pole near the optic nerve;
the shorter tick marks represent 0.5-mm increments along the retinal
surface.