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  Discussion on Research Study: Comparison of high-field and low-field magnetic resonance images
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Moderator:
DrO

Posted on Thursday, Nov 12, 2009 - 6:36 am:

Though there are some practical reasons to use low-field MRI for imaging a lame horse's leg, where possible high field machines should be used. Both normal tissues and pathological findings were better visualized in this study. This is particularly true in pain referable to a joint as articular surfaces were not well visualized in the low field machines.
DrO


Vet Rec. 2009 Sep 5;165(10):281-288.
Comparison of high-field and low-field magnetic resonance images of cadaver limbs of horses.

Murray RC, Mair TS, Sherlock CE, Blunden AS.

Animal Health Trust, Lanwades Park, Kentford, Newmarket CB8 7UU.

Eleven limbs taken postmortem from 10 lame horses were examined by MRI in a low-field 0.27T system designed for standing horses and a high-field 1.5T system used to examine anaesthetised horses. Nine limbs were examined in the foot/pastern region and two in the fetlock region, and the results were compared with gross pathological examinations and histological examinations of selected tissues. The appearance of normal tissues was similar between the two systems, but the anatomical arrangement of the structures was different due to differences in positioning, and a magic angle artefact was observed at different sites in some imaging sequences. Articular cartilage could be differentiated into two articular surfaces in most joints in the high-field images but could generally be separated only at the joint margins in the low-field images. Abnormalities of tendon, ligament and bone detected by gross examination were detected by both forms of MRI, but some details were clearer on the high-field images. Articular cartilage found to be normal on pathological examination was also classified as normal on MRI, but lesions in articular cartilage detected on pathological examination were identified only by high-field MRI. An abnormality was detected on MRI of all the limbs that had abnormal navicular flexor fibrocartilage on pathological examination.
Member:
digger89

Posted on Monday, Feb 28, 2011 - 6:34 pm:

My coming 10 year old paint developed heel pain in his left front foot last summer. A low resolution MRI was done, and navicular changes to both feet was seen. He also had soft tissue inflammation on the left which was thought to be the real cause of the pain. We have not been able to make him sound at the trot since then, in spite of Tildren, steroid injections, stall rest, several different shoes/pads, and magnetic bell boots (although they only lasted one week before he destroyed them beyond repair). We are considering another MRI. I understand that the high resolution MRI entails general anesthesia. Dakota has a history of mild RER (recurrent exertional rhabdomyolysis). It has been well controlled with a high fat - low starch diet and consistent exercise. No specific tying up episodes were ever noticed, only a frequent muscle soreness. His muscle enzymes were elevated. Muscle biopsy was negative for PSSM. Is he at risk for malignant hyperthermia or any other issues because of his RER? Thanks. Sarah
Moderator:
DrO

Posted on Monday, Feb 28, 2011 - 9:28 pm:

Hello Sarah,
Yes there is a risk even with horses with no history of problems. Considering the history you give it is nearly impossible to evaluate how much greater the risk is in your horse but assuming you now have a clinically normal horse and if the enzymes are normal it does not strike me as much higher.
DrO
Member:
digger89

Posted on Monday, Feb 28, 2011 - 10:03 pm:

Thank you Dr. O. Have you ever seen any reports or studies on general anesthesia in horses with these types of muscle diseases? Sarah
Moderator:
DrO

Posted on Tuesday, Mar 1, 2011 - 6:10 pm:

The problem here Sarah is we don't know what type muscle disease your horse has or even whether he still suffers from the problem. This is possibly due to the good care you are giving. There are reports that suggest horses with moderate to severe tying up synDrOmes have more problems with MH or post anesthetic episodes of tying up. This is one example:
J Am Vet Med Assoc. 1990 Apr 1;196(7):1077-83.

Contracture test and histologic and histochemical analyses of muscle biopsy specimens from horses with exertional rhabdomyolysis.
Hildebrand SV, Arpin D, Cardinet G 3rd.

Department of Veterinary Surgery, School of Veterinary Medicine, University of California, Davis 95616.

Abstract
Biopsy specimens of the cutaneous omobrachialis muscle were obtained from 10 horses with a problem of myositis from mild exercise. One horse had been evaluated previously and malignant hyperthermia-like contractures developed in its muscle biopsy specimen during the contracture test. In this study, the halothane-caffeine contracture test and histologic and histochemical evaluations were performed on muscle biopsy specimens. In the contracture test, no muscle biopsy specimen developed contracture in the presence of 2 or 4% halothane alone. The mean (+/- SEM) caffeine-specific concentration in the presence of halothane was 5.23 +/- 0.5 mM for 2% halothane, and 4.46 +/- 0.6 mM for 4% halothane. The caffeine-specific concentration values were not significantly different. Contracture response for any muscle specimen did not resemble contracture associated with malignant hyperthermia. The cutaneous omobrachialis muscle was composed of type-II fibers, with type-I fibers seldom seen. For 9 of the 10 horses, overall fiber morphology was normal; 1 horse had necrotic fibers. Of the 10 muscle specimens, 9 had fibers that had positive reaction for alkaline phosphatase activity; 3 muscle specimens contained ringed myofibers. Three horses of this study were administered general anesthesia; 2 were research horses, anesthetized with halothane and succinylcholine, and 1 was a clinical case given halothane anesthesia plus a non-depolarizing muscle relaxant. One research horse developed a malignant hyperthermia-like reaction to anesthesia, with severe rhabdomyolysis evident after anesthesia, and an episode of muscle cramping in its stall 2 days after anesthesia. The other 2 horses had unremarkable postanesthetic periods.


Be sure you read our articles on tying up and malignant hyperthermia for more information.
DrO
Member:
digger89

Posted on Tuesday, Mar 1, 2011 - 6:49 pm:

Thank you for your help. If we go ahead with the high field MRI and general anesthesia I will let you know how he does Sarah
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