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Magnetic Resonance Imaging Artifacts Induced by Ocular Prosthesis
262
AMERICAN JOURNAL OF OPHTHALMOLOGY
August, 1994
4. Lakhanpal, V., Schocket, S. S., and Jiji, R.: Deferoxamine (Desferal)-induced toxic retinal pigmen tary degeneration and presumed optic neuropathy. Ophthalmology 91:443, 1984. 5. Olivieri, N. F., Buncic, J. R., Chew, E., Gallant, T., Harrison, R. V., Keenan, N., Logan, W., Mitchell, D., Ricci, G., Skarf, B., Taylor, M., and Freedman, M. H.: Visual and auditory neurotoxicity in patients receiving subcutaneous deferoxamine infusions. N. Engl. J. Med. 314:869, 1986.
Magnetic Resonance Imaging Artifacts Induced by Ocular Prosthesis Constance L. Fry, M.D., and Barrett G. Haik, M.D. Department of Ophthalmology, Tulane University School of Medicine. Supported by St. Giles Founda tion, New York, New York. Inquiries to Barrett G. Haik, M.D., Department of Ophthalmology, Tulane University School of Medicine, 1430 Tulane Ave., New Orleans, LA 70112. Magnetic resonance imaging is increasingly used to monitor anophthalmic sockets for tu mor recurrence. The popularity of magnetic resonance imaging is in part a result of its superb contrast resolution and its ability to delineate soft tissue better than computed to mography. Unfortunately, artifacts may mark edly degrade the image on magnetic resonance imaging. Although most artifacts are produced by metallic implants (that is, dental work, sur gical clips, wires, screws, and plates), others are created by particulate metals. Linear densities and distortion of the globe have been caused by iron oxide particles in eyelid tattooing and mascara. 1 · 2 We observed a case of a child with an anophthalmic socket, in whom the prosthetic eye produced significant artifact. This 2y2-year-old girl had a history of bi lateral retinoblastoma. She had undergone enucleation of the more severely involved left eye and external beam irradiation therapy to the right globe. She was subsequently referred to our oncology service with a computed tomographic scan and a magnetic resonance image after explosive tumor growth was noted in the remaining eye. The computed tomographic scan (Fig. 1) showed the left orbital implant with an overlying prosthesis. The borders of the prosthesis were clearly demonstrated, although soft tissue details were lacking. Conversely, on
Fig. 1 (Fry and Haik). Computed tomographic scan of left orbital implant and prosthesis.
T]- and T 2 -weighted images (Fig. 2) structures immediately adjacent to the prosthesis were obscured by a signal void created by the pros thesis. A prosthesis is made of primarily methylmethacrylate monomer, with an acrylic disk, oil-based paint, and silk threads. However, there are trace minerals in the paint, including barium, cadmium, lead, and cobalt. Additional ly, the scierai vessels are made of a combination of titanium dioxide (95%), aluminum hydrox ide (4%), and silica (1%). Although these ele ments are present only in traces, as little as 1 mg of powdered metallic alloy has created arti facts on in vitro testing. 3 Significant artifacts are generated by ferro magnetic objects. However, nonferromagnetic substances, such as titanium, can also produce smaller distortions. These artifacts are a result of several factors. Any metal in a static field will create some distortion. This distortion is ampli fied by patient movement. Eddy currents are produced by placing the material within a changing magnetic field. These currents pro duce magnetic fields that distort the main field and degrade the image quality. 4 The radiofrequency pulse also generates a current within the metal which induces artifacts. Although these types of artifact are small and would not affect the entire orbit, a signal void may prevent adequate visualization of immediately adjacent tissues. 5
Vol. 118, No. 2
Correspondence
263
Correspondence Correspondence concerning recent articles or other mate rial published in THE JOURNAL should be submitted within six weeks of publication. Correspondence must be typed double-spaced, on 8Î/2 x 11-inch bond paper with lî/2-inch margins on all four sides and should be no more than two typewritten pages in length. Every effort will be made to resolve controversies between the correspondents and the authors of the article before publication.
The Pros and Cons of Laser Dacryocystorhinostomy
Fig. 2 (Fry and Haik). T,- (top) and T2- (bottom) weighted images showing the image distortion adja cent to the prosthesis.
Care s h o u l d be t a k e n to r e m i n d the r a d i o l o g y suites to r e m o v e the ocular p r o s t h e s i s before m a g n e t i c r e s o n a n c e i m a g i n g of the orbit in order to obtain m a x i m u m benefit from the study.
References 1. Lund, G., Wirtschafter, J. D., Nelson, J. D., and Williams, P. A.: Tattooing of eyelids. Magnetic reso nance imaging artifacts. Ophthalmic Surg. 17:550, 1986. 2. Weiss, R. A., Saint-Louis, L. A., Haik, B. G., McCord, C. D., and Taveras, J. L.: Mascara, eyelining tattoos. MRI artifacts. Ann. Ophthalmol. 21:129, 1989. 3. Weyrich, G., Sigmund, G., Schlickewei, W., and Vinee, P.: Metallabrieb als bildartefakt im kernspintomogramm. Radiologe 33:367, 1993. 4. Kelly, W. M.: Image artifacts and technical limi tations. In Brant-Zawadzki, M., and Norman, D. (eds.): Magnetic Resonance Imaging of the Central Nervous System. New York, Raven Press, 1987, pp. 43-82. 5. Shellock, F. G., Mink, J. H., Curtin, S., and Friedman, M. J.: MR imaging and metallic implants for anterior cruciate ligament reconstruction. Assess ment of ferromagnetism and artifact. J. Magn. Reson. Imaging 2:225, 1992.
EDITOR: In the Perspective, " T h e p r o s a n d cons of laser d a c r y o c y s t o r h i n o s t o m y , " by G. B. Bartley (Am. J. O p h t h a l m o l . 117:103, J a n u a r y 1994), the a u t h o r ' s insightful c o m m e n t s on the pros a n d cons of laser dacryocystorhinostomy are welcome a n d s h a r e d by m a n y lacrimal sur g e o n s . I was particularly i m p r e s s e d by the esti m a t e d increased operative cost of $300.00 (in 1990) for laser-assisted d a c r y o c y s t o r h i n o s t o m y over a traditional incisional d a c r y o c y s t o r h i n o s tomy. 1 This a m o u n t s u p p o s e d l y covers the additional 30 to 60 m i n u t e s of o p e r a t i n g r o o m - t i m e charges, hospital laser u s a g e fee, a n d video e n d o s c o p i e usage fees. This also as s u m e s n o p r e m i u m on the s u r g e o n ' s fee for "laser s u r g e r y . " It is a p p a r e n t that the h e a l t h care dollar in H o u s t o n d o e s n o t stretch as far as it does in other p a r t s of the c o u n t r y . JAMES R. PATRINELY, M.D. Houston, Texas
Reference 1. Gonnering, R. S., Lyon, D. B., and Fisher, J. C : Endoscopie laser-assisted lacrimal surgery. Am. J. Ophthalmol. 111:152, 1991.
Arteriovenous Crossing as a Risk Factor in Branch Retinal Vein Occlusion EDITOR: The recent article, " A r t e r i o v e n o u s crossing as a risk factor in b r a n c h retinal vein occlu s i o n , " by G. S t a u r e n g h i , C. Lonati, M. Asche-
AMERICAN JOURNAL OF OPHTHALMOLOGY
August, 1994
4. Lakhanpal, V., Schocket, S. S., and Jiji, R.: Deferoxamine (Desferal)-induced toxic retinal pigmen tary degeneration and presumed optic neuropathy. Ophthalmology 91:443, 1984. 5. Olivieri, N. F., Buncic, J. R., Chew, E., Gallant, T., Harrison, R. V., Keenan, N., Logan, W., Mitchell, D., Ricci, G., Skarf, B., Taylor, M., and Freedman, M. H.: Visual and auditory neurotoxicity in patients receiving subcutaneous deferoxamine infusions. N. Engl. J. Med. 314:869, 1986.
Magnetic Resonance Imaging Artifacts Induced by Ocular Prosthesis Constance L. Fry, M.D., and Barrett G. Haik, M.D. Department of Ophthalmology, Tulane University School of Medicine. Supported by St. Giles Founda tion, New York, New York. Inquiries to Barrett G. Haik, M.D., Department of Ophthalmology, Tulane University School of Medicine, 1430 Tulane Ave., New Orleans, LA 70112. Magnetic resonance imaging is increasingly used to monitor anophthalmic sockets for tu mor recurrence. The popularity of magnetic resonance imaging is in part a result of its superb contrast resolution and its ability to delineate soft tissue better than computed to mography. Unfortunately, artifacts may mark edly degrade the image on magnetic resonance imaging. Although most artifacts are produced by metallic implants (that is, dental work, sur gical clips, wires, screws, and plates), others are created by particulate metals. Linear densities and distortion of the globe have been caused by iron oxide particles in eyelid tattooing and mascara. 1 · 2 We observed a case of a child with an anophthalmic socket, in whom the prosthetic eye produced significant artifact. This 2y2-year-old girl had a history of bi lateral retinoblastoma. She had undergone enucleation of the more severely involved left eye and external beam irradiation therapy to the right globe. She was subsequently referred to our oncology service with a computed tomographic scan and a magnetic resonance image after explosive tumor growth was noted in the remaining eye. The computed tomographic scan (Fig. 1) showed the left orbital implant with an overlying prosthesis. The borders of the prosthesis were clearly demonstrated, although soft tissue details were lacking. Conversely, on
Fig. 1 (Fry and Haik). Computed tomographic scan of left orbital implant and prosthesis.
T]- and T 2 -weighted images (Fig. 2) structures immediately adjacent to the prosthesis were obscured by a signal void created by the pros thesis. A prosthesis is made of primarily methylmethacrylate monomer, with an acrylic disk, oil-based paint, and silk threads. However, there are trace minerals in the paint, including barium, cadmium, lead, and cobalt. Additional ly, the scierai vessels are made of a combination of titanium dioxide (95%), aluminum hydrox ide (4%), and silica (1%). Although these ele ments are present only in traces, as little as 1 mg of powdered metallic alloy has created arti facts on in vitro testing. 3 Significant artifacts are generated by ferro magnetic objects. However, nonferromagnetic substances, such as titanium, can also produce smaller distortions. These artifacts are a result of several factors. Any metal in a static field will create some distortion. This distortion is ampli fied by patient movement. Eddy currents are produced by placing the material within a changing magnetic field. These currents pro duce magnetic fields that distort the main field and degrade the image quality. 4 The radiofrequency pulse also generates a current within the metal which induces artifacts. Although these types of artifact are small and would not affect the entire orbit, a signal void may prevent adequate visualization of immediately adjacent tissues. 5
Vol. 118, No. 2
Correspondence
263
Correspondence Correspondence concerning recent articles or other mate rial published in THE JOURNAL should be submitted within six weeks of publication. Correspondence must be typed double-spaced, on 8Î/2 x 11-inch bond paper with lî/2-inch margins on all four sides and should be no more than two typewritten pages in length. Every effort will be made to resolve controversies between the correspondents and the authors of the article before publication.
The Pros and Cons of Laser Dacryocystorhinostomy
Fig. 2 (Fry and Haik). T,- (top) and T2- (bottom) weighted images showing the image distortion adja cent to the prosthesis.
Care s h o u l d be t a k e n to r e m i n d the r a d i o l o g y suites to r e m o v e the ocular p r o s t h e s i s before m a g n e t i c r e s o n a n c e i m a g i n g of the orbit in order to obtain m a x i m u m benefit from the study.
References 1. Lund, G., Wirtschafter, J. D., Nelson, J. D., and Williams, P. A.: Tattooing of eyelids. Magnetic reso nance imaging artifacts. Ophthalmic Surg. 17:550, 1986. 2. Weiss, R. A., Saint-Louis, L. A., Haik, B. G., McCord, C. D., and Taveras, J. L.: Mascara, eyelining tattoos. MRI artifacts. Ann. Ophthalmol. 21:129, 1989. 3. Weyrich, G., Sigmund, G., Schlickewei, W., and Vinee, P.: Metallabrieb als bildartefakt im kernspintomogramm. Radiologe 33:367, 1993. 4. Kelly, W. M.: Image artifacts and technical limi tations. In Brant-Zawadzki, M., and Norman, D. (eds.): Magnetic Resonance Imaging of the Central Nervous System. New York, Raven Press, 1987, pp. 43-82. 5. Shellock, F. G., Mink, J. H., Curtin, S., and Friedman, M. J.: MR imaging and metallic implants for anterior cruciate ligament reconstruction. Assess ment of ferromagnetism and artifact. J. Magn. Reson. Imaging 2:225, 1992.
EDITOR: In the Perspective, " T h e p r o s a n d cons of laser d a c r y o c y s t o r h i n o s t o m y , " by G. B. Bartley (Am. J. O p h t h a l m o l . 117:103, J a n u a r y 1994), the a u t h o r ' s insightful c o m m e n t s on the pros a n d cons of laser dacryocystorhinostomy are welcome a n d s h a r e d by m a n y lacrimal sur g e o n s . I was particularly i m p r e s s e d by the esti m a t e d increased operative cost of $300.00 (in 1990) for laser-assisted d a c r y o c y s t o r h i n o s t o m y over a traditional incisional d a c r y o c y s t o r h i n o s tomy. 1 This a m o u n t s u p p o s e d l y covers the additional 30 to 60 m i n u t e s of o p e r a t i n g r o o m - t i m e charges, hospital laser u s a g e fee, a n d video e n d o s c o p i e usage fees. This also as s u m e s n o p r e m i u m on the s u r g e o n ' s fee for "laser s u r g e r y . " It is a p p a r e n t that the h e a l t h care dollar in H o u s t o n d o e s n o t stretch as far as it does in other p a r t s of the c o u n t r y . JAMES R. PATRINELY, M.D. Houston, Texas
Reference 1. Gonnering, R. S., Lyon, D. B., and Fisher, J. C : Endoscopie laser-assisted lacrimal surgery. Am. J. Ophthalmol. 111:152, 1991.
Arteriovenous Crossing as a Risk Factor in Branch Retinal Vein Occlusion EDITOR: The recent article, " A r t e r i o v e n o u s crossing as a risk factor in b r a n c h retinal vein occlu s i o n , " by G. S t a u r e n g h i , C. Lonati, M. Asche-