Anesthesia, RectalAnalgesics, OpioidPain, PostoperativeInfusions, IntralesionalAnalgesia, Patient-ControlledMorphinePain MeasurementReceptors, Opioid, muReceptors, OpioidReceptors, Opioid, deltaReceptors, Opioid, kappaOpioid PeptidesNarcotic AntagonistsNaloxoneOpioid-Related DisordersMultimodal ImagingNaltrexoneEnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-NarcoticsEnkephalin, D-Penicillamine (2,5)-EndorphinsDynorphinsBuprenorphineEnkephalin, LeucinePainEnkephalin, Leucine-2-AlanineAnalgesiaAnalgesicsDiprenorphineMagnetic Resonance Imagingbeta-EndorphinBenzeneacetamidesDrug ToleranceMorphinansFentanylMethadoneCombined Modality TherapyMolecular ImagingHydromorphoneBrainChronic PainBenzomorphansPyrrolidinesSubstance Withdrawal SyndromeOpiate Substitution TreatmentDiagnostic ImagingSubtraction TechniqueAnalgesics, Non-NarcoticBrain MappingDose-Response Relationship, DrugTreatment OutcomeHeroinPostoperative Nausea and VomitingPositron-Emission TomographyPrescription Drug Misuse