Page 127 - Feline diagnostic imaging

References 125
muscles. Choroid is hyperintense relative to vitreous
and sclera on T1W. The lens capsule has a signal
intensity between the fat and extraocular muscles
[4,49,50].
The T2W has the best soft tissue contrast and is typi-
cally better than T1W imaging for demonstrating orbital
pathology (Figure 7.21) [46]. The hallmark of a T2 image
of the orbit is the bright signal intensity of vitreous, the
absolute intensity of which depends on the magnetic
strength of the scanner. The relative order of signal
intensity on T2 images is, from high to low, vitreous
and aqueous, extraocular muscles/optic nerve, and fat
[4,9,50].
The optic nerve has a moderately high signal intensity
on T1W whereas it is moderately low intensity on T2W,
compared with the vitreous humor. However, since
orbital fat has very low intensity on T2W, the optic
nerve and chiasm can be visualized much better on
T2W images [49].
Figure 7.21 T2W image (transverse plane) showing the
characteristic bright signal intensity of the vitreous.

References

1 Eisenberg, H.M. (1985). Ultrasonography of the eye and 10 Dietrich, U.M. (2013). Ophthalmic examination and
orbit. Vet. Clin. North Am. Small Anim. Pract. 15: diagnostic: part 3: diagnostic ultrasonography. In:
1263–1274. Veterinary Ophthalmology., 5e (eds. K.N. Gelatt, B.C.
2 Hager, D.A., Dziezyc, J., and Millichamp, N.J. (1987). Gilger and T.J. Kern), 669–683. Ames: Wiley.
Two‐dimensional real‐time ocular ultrasonography in the 11 Scotty, N.C. (2005). Ocular ultrasonography in horses.
dog. Technique and normal anatomy. Vet. Radiol. 28: Clin. Tech. Equine. Pract. 4: 106–113.
60–65. 12 Spaulding, K. (2008). Eye and orbit. In: Atlas of
3 Williams, J. and Wilkie, D.A. (1996). Ultrasonography of Small Animal Ultrasonography, 1e (eds. D. Penninck
the eye. Comp. Cont. Educ. Vet. 18: 667–677. and M.A. d’Anjou), 49–90. Oxford: Blackwell
4 Penninck, D., Daniel, G.B., Brawer, R., and Tidwell, A.S. Publishing.
(2001). Cross‐sectional imaging techniques in veterinary 13 Schiffer, S.P., Rantanen, N.W., Leary, G.A. et al. (1982).
ophthalmology. Clin. Tech. Small. Anim. Pract. 16: 22–39. Biometric study of the canine eye, using A‐mode
5 Blaivas, M. (2000). Bedside emergency department ultrasonography. Am. J. Vet. Res. 43: 826–830.
ultrasonography in the evaluation of ocular pathology. 14 Byrne, S.F. and Green, R.L. (2010). Physics and
Acad. Emerg. Med. 7: 947–950. instrumentation. In: Ultrasound of the Eye and Orbit, 2e
6 Daniel, G.B. and Mitchell, S.K. (1999). The eye and orbit. (eds. S.D. Byrne and R.L. Green), 1–13. New Delhi: Jaypee
Clin. Tech. Small. Anim. Pract. 14: 160–169. Brothers Medical Publishers Ltd.
7 Mattoon, J.S. and Nyland, T.G. (2002). Eye. In: Small 15 Ossoinig, K.C. (1979). Standardized echography: basic
Animal Diagnostic Ultrasound, 2e (eds. T.G. Nyland and principles, clinical applications, and results. Int.
J.S. Mattoon), 305–323. Philadelphia: WB Saunders. Ophthalmol. Clin. 19: 127–210.
8 Boroffka, S.A., Verbruggen, A.M., Grinwins, G.C. et al. 16 Coleman, D.J., Dallow, R.L., and Smith, M.E. (1979). A
(2007). Assessment of ultrasonography and computed combined system of contact A‐scan and B‐scan. Int.
tomography for the evaluation of unilateral orbital disease Ophthalmol. Clin. 19: 211–224.
in dogs. J. Am. Vet. Med. Assoc. 230: 671–680. 17 Hamidzada, W.A. and Osuobeni, E.P. (1999). Agreement
9 Dennis, R. (2000). Use of magnetic resonance imaging for between A‐mode and B‐mode ultrasonography in the
the investigation of orbital disease in small animals. measurement of ocular distances. Vet. Radiol. Ultrasound
J. Small Anim. Pract. 41: 145–155. 40: 502–507.