Luteal and follicular count in bitches : assessment by means of magnetic resonance imaging

Abstract

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Researchers require an accurate measurement of fertility in the bitch for the comparison ofinsemination methods, assessing the effects of procedures on fertility and assessing the effectsof drugs on fertility. In clinical practice, a prospective measurement would enable thepractitioner to select bitches with the largest numbers of follicles for breeding by artificialmeans or natural mating with valuable semen or studs. The ratio between the numbers ofcorpora lutea or follicles and litter size is a more sensitive measurement of fertility than islitter size, as the latter does not reflect the total number of oocytes that were available forfertilization. Magnetic resonance imaging (MRI) has proven to be of value in diagnosticimagery of particularly soft tissues. This is the first study that evaluated the use of MRI incanine reproduction and was done to determine whether the numbers of corpora lutea orfollicles can be counted accurately by means of MRI.The study was divided into two experiments. In Experiment 1, 16 bitches were used. Apartfrom one bitch that was in anoestrus, they were either in the follicular, early, or late lutealphase. Their ovaries were collected via ovariohysterectomy and placed into a phantom forMRI. The phantom was then scanned in three planes with a slice interval and slice thickness of 1 mm, using a 1.5 Tesla SIEMENS Magnetom Symphony scanner. A circular polarizedhead array coil was also used around the phantom. The T2-weigthed images were consideredbetter than T1-weighted images. This study showed that although the corpora lutea or folliclescould be identified in most but not all images, it was not possible to accurately count thenumber of corpora lutea or follicles in the ovaries of bitches using MRI techniques andapparatus commonly used in human MRI units. Follicles were commonly confused withcorpora lutea on the images. Although the study was not designed to detect ovarian pathology,MRI of the ovary in the phantom study, showed promise in detecting cystic ovarian disease.In Experiment 2, it was attempted to find the ovaries, and count the structures in them, bydoing MRI on two live, sedated bitches that were in the late follicular phase, whereafter thebitches were spayed and the ovarian structures counted. The effect of motion was so great thatno image could be generated on which any ovary or its structures could be identified.There still exists no reliable, non-invasive means by which the number corpora lutea orfollicles can be counted in the bitch. Further studies are required to evaluate more advancedMRI techniques and apparatus.

Navorsers benodig 'n akurate meting van vrugbaarheid in die teef vir die vergelyking vaninseminasiemetodes en vir die beoordeling van die effekte van prosedures en middels opvrugbaarheid. In praktyk sou veral 'n prospektiewe meting van vrugbaarheid nuttig wees,omdat dit die klinikus in staat sal stel om daardie tewe met die grootste aantal follikels teselekteer vir teling in gevalle waar die koste van òf die semen òf dekking baie hoog is. Dieverhouding tussen die aantal korpora lutea of follikels en werpselgrootte is 'n sensitiewermaatstaf van vrugbaarheid as werpselgrootte op sigself; omdat laasgenoemde nie dievolledige aantal oösiete wat beskikbaar was vir bevrugting in bereken bring nie. Magnetieseresonansie beelding (MRB) is reeds bewys as 'n waardevolle tegniek vir die verkryging vandiagnostiese beelde van veral sagte weefsels. Hierdie is die eerste studie wat die gebruik vanMRB op die geslagstelsel van honde beoordeel en was spesifiek uitgevoer om vas te stel ofdie korpora lutea of follikels in die eierstokke van tewe d.m.v. MRB akkuraat getel kan word.Die studie was verdeel in 2 eksperimente. In Eksperiment 1 was 16 tewe gebruik. Behalwe vireen teef wat in anestrus was, was hulle òf in die follikulêre fase, òf in die vroeë òf in die laatluteale fases. Hul eierstokke was versamel deur middel van ovariohistorektomie en in 'nfantoom geplaas vir MRB. Die fantoom was geskandeer in drie oriëntasies reghoekig totmekaar, en 'n snitdikte en 'n snitinterval van 1mm is gebruik. Die MRB aparaat was 'n 1.5 Tesla SIEMENS Magnetom Symphony skandeerder. 'n Kopspoel was gebruik rondom diefantoom. Die T2-gerigte beelde was beter as die T1-gerigte beelde. Hierdie studie het getoondat alhoewel die korpora lutea of follikels in die meeste beelde van die eierstokkegeïdentifiseer kan word, dit nie moontlik is om hierdie strukture in die eierstokke van tewe tetel m.b.v. die apparaat wat oor die algemeen in die gemidelde privaathospitaal beskikbaar isnie. Dit was ook nie moontlik om altyd korpora lutea van follikels te onderskei nie. Alhoeweldie studie nie ontwerp was om vir patologiese letsels op die eierstokke te soek nie, was diemeeste ovariële siste duidelik sigbaar op die beelde in die fantoomstudie, wat daarop dui datMRB in hierdie verband belowend mag wees.In Eksperiment 2 is gepoog om die eierstokke in twee lewendige tewe wat laat in diefollikulêre fase en onder berusting was, d.m.v. MRB op te spoor en die strukture daarin te tel,waarna 'n ovariohisterektomie op elke teef uitgevoer was en die strukture getel was. Die effekvan beweging wat deur asemhaling teweeg gebring is was egter só groot dat daar geen beeldgegenereer kon word waarop 'n eierstok of sy strukture herken kon word nie.Daar bestaan steeds geen betroubare manier, anders as disseksie van die eierstokke, om diefollikels of korpora lutea indie eierstokke van tewe akkuraat te tel nie. Verdere navorsing isnodig om meer gevorderde MRB tegnieke en apparaat vir hierdie doel te evalueer.