Case 20 cont'd
Image findings: This is a 75SeHCAT study! these images were obtained during counting the patient's and the backgroung's activity. The patient was a 53F, status post cholecystectomy with chronic diarrhea. Using 23-[75Se]selena-25-homotaurochoic acid, we can evaluate enterohepatic circulation of bile acid to assess Bile Acid Malabsorption (BAM). This radiopharmaceutical acts in the same manner as natural bile acids.
The measured activity of the patient on the day 0 and 1 as follows:
Retention(corrected for decay) : 17%
75SeHCAT technique:
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Traditionally used whole body counters but these are not practically available
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Gamma camera techniques used as counting devices rather than imaging devices
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Use uncollimated detectors ( bare crystal ):
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Risk of crystal breakage
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Risk of disabled pressure detectors
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Give 370 kBq SeHCAT capsule
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On day 0
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Take 5 minute background and 5 minute patient measurement
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On day 7
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Take 5 minute background and 5 minute patient measurement
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T1/2 75Se = 120 days
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Decay mode : electron capture --> 75As
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136 keV (58%); 264 keV (58%); 279 keV (25%)
Pathophysiology :
Enterohepatic Circulation
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Bile acids excreted from liver
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Bile acids absorbed from terminal ileum (Approx. 95%)
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If there is any bile acid malabsorption a large amount of bile acid enter the colon.
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This cycle occurs 5 times per 24 hours.
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SeHCAT follows this physiology
Bile Acid Malabsorption (BAM):
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Bile Acid is a colonic irritant --> Diarrhea
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Increased fat in colon --> Diarrhea
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Clinical problem:
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Diarrhea predominant IBS occurs in 1% of population
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Approx. 1/3 of these related to BAM
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Can be effectively treated with bile acid sequestrants (ie. Cholestyramine)
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Refference: www.mayoclinic.org
Notghi et al., Nuc Med Comm 2011;32:960-966
75SeHCAT interpretation:
background and decay corrected day 7 counts x100
% retention = ----------------------------------------------------------------------------------
background corrected day 1 counts
Normal ranges (7 days):
Retention of < 10% --> Abnormal ileal bile acid absorption
Retention of > 15% --> Normal ileal bile acid absorption
Retention of 10%- 15% --> Borderline ileal bile acid absorption
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At or below 10% expected to respond to therapy
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Normal:15% retention or greater
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Indeterminate:
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10-15% may represent mild BAM but unlikely to respond to therapy
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Source: Notghi et al., Nuc Med Comm 2011;32:960-966