Physicians and possibly medical students and paramedics.

Transcription

1 MYCIN Introduction Problem domain: Selection of antibiotics for patients with serious infections. Medical decision making, particularly in clinical medicine is regarded as an "art form" rather than a "scientific discipline": this knowledge must be systemised for practical day-to-day use and for teaching and learning clinical medicine. Target Users: Physicians and possibly medical students and paramedics. Originators: Edward Shortliffe, (1972) Department of Medicine and Computer Science, Heuristic Programming Project, Stanford University School of Medicine, Stanford, CALIFORNIA References: Shortliffe, Edward H.(1981), "CONSULTATION SYSTEMS FOR PHYSICIANS: The Role of Artificial Intelligence Techniques". In Webber, Bonnie L.and Nilsson, Nils J. (Eds.). Readings in Artificial Intelligence. pp Tioga Publishing Company. Palo Alto, California.

2 Why choose MYCIN? "MYCIN developed at Stanford in the mid-1970s, was one of the first programs to address the problems of reasoning with uncertain or incomp lete information. MYCIN provided clear and logical explanation of the reasoning, used a control structure appropriate to the specific problem domain, and identified criteria to reliably evaluate its performance. Many of the expert system development techniques currently in use were first developed in the MYCIN project."

3 How does it work? DETAILS OF NEW CASE user ADVICE & EXPLANATIONS user interface knowledge base inference strategy expert system building tools knowledge engineer domain expert

4 What does it do? Diagnose inf ect ious disease and recommend appropriat e t herapy. Is t here a significant infect ion which requires t reat ment? What is t he ident it y of t he organism? What are t he pot ent ially useful drugs? Which drug or drugs will be best for t he pat ient?

5 MYCIN -- A typical consultation 1. Patient s name: (first - last) ** FRED BRAUN (Questions 1-3 requestbackground patient data). 2. Sex: ** M 3. Age: ** Are there any cultures for Fred Braun which may be related to the present illness, and from which organisms have been grown successfully in the microbiology laboratory? ** Y CULTURE From what site was the specimen for CULTURE - 1 taken? ** BLOD = BLOOD (System corrects typing error). 6. Please give the date and time when CULTURE-1 was obtained. (mo/da/yr time) ** JUN 20, 1977 The first organism isolated from the blood culture of 20-JUN-77 (CULTURE-1) will be referred to as: ORGANISM Enter the laboratory - reported identity of ORGANISM-1: ** UNKNOWN (Typically identity is not known yet). 8. The strain (gram or Ziehl-Neelsen acid-fast) of ORGANISM-1: ** NEG (Preliminary lab results give some clues). 9. Is ORGANISM - 1 rod or coccus (etc.): ** ROD 10. What is the form of the individual organisms (e.g. lancetshaped for cocci, fusiform for rods, etc)? ** FUSIFORM (... more questions follow in order to gather sufficient information to infer the identity and significance of the infecting organisms...) 23. What is the suspected portal of entry of the gramneg rod from the blood culture of 20-JUN-77 (ORGANISM-1) into this sterile site? ** GI (6) (User indicates the uncertainty of his response). 24. Is Fred Braun a burn patient? ** N 25. Is Fred Braun a compromised host (e.g. alcoholic, sickle-cell-disease, immunosuppressed)? ** N 26. Is Fred Braun febrile? ** Y (... after about questions, MYCIN prints the diagnostic hypotheses on which therapy will be based...)

6 My therapy recommendations will be designed to treat for organisms that are either very likely, or, although less likely, would have a significant effect on therapy selection if they were present. It is important to cover for the following probable infection(s) and associated organism(s): INFECTION-1 is BACTEREMIA <ITEM-1> E.COLI [ORGANISM-1] <ITEM-2> KLEBSIELLA [ORGANISM-1] <ITEM-3> ENTEROBACTER [ORGANISM-1] <ITEM-4> KLEBSIELLA-PNEUMONIAE [ORGANISM-1] ** WHAT DOES GU MANIPULATION TELL YOU ABOUT THE IDENTITY OF AN ORGANISM? The rules listed below use: whether the patient has had a genito-urinary manipulative procedure to conclude about: the identity of the organism 156, 163, 190 Which do you wish to see? ** 156 RULE 156 IF: 1. The site of the culture blood, and 2. The gram stain of the organism is gramneg, and 3. The morphology of the organism is rod, and 4. The portal of entry of the organism is urine, and 5. The patient has not had a genito-urinary manipulative procedure, and 6. Cystitis is not a problem for which the patient has been treated THEN: There is suggestive evidence (.6) that the identity of the organism is e.coli ** IS BLOOD A STERILE SITE? Yes. Blood is one of those sites that is normally sterile. ** WHAT ARE THE NONSTERILE SITES? Those sites that are normally nonsterile are: CERVIX, CUTANEOUS-ULCER, LOCHIA, NOSE, SKIN, STOOL, THROAT, URETHRA, VAGINA. ** IS BACTEROIDES AEROBIC? No, the aerobicity of bacteroides is anaerobic.

7 Dynamic knowledge - st ruct ure pat ient cult ure1 cult ure2 operat ion organism1 organism2 organism3 drug5 drug1 drug2 drug3 drug4 Context tree

8 Implementation and Algorithms How MYCIN works 1. Create patient 'context' tree 2. Is there an organism that requires therapy? 3. Decide which drugs are potentially useful and select the best drug The above is a goal-oriented backward chaining approach to rule invocation & question selection. MYCIN accomplishes the invocation and the selection through two procedures: MONITOR and FINDOUT -- procedures developed by the MYCIN development team:

9 How MYCIN Works MONITOR (for MYCIN rules) attempts to evaluate the premise of the current rule, condition by condition. If any of the conditions is false, or indeterminate due to lack of information, the rule is rejected, and the next rule on the list of applicable rules pending in the current context is tried. The rule application succeeds when all of the conditions in the premise are deemed to be true, and the conclusion of the rule is added to the record of the current consultation:

10 Start Consider the 1st condition in the premise of the rule Gather the necessary information using the FINDOUT mechanism no Has all necessary information been gathered to decide if the condition is true yes Consider the next condition in the premise of the rule yes Is the condition TRUE? yes Are there more conditions to check? REJECT THE RULE no (or unknown) no Add the conclusion of the rule to the ongoing record of the current consultation EXIT EXIT

11 How MYCIN Works FINDOUT (Mechanism) searches for data needed by the MONITOR procedure, particularly the MYCIN 'clinical' parameters referenced in the conditions which are not known. Essentially FINDOUT gathers the information that will count for or against a particular condition in the premise of the rule under consideration. If the information required is laboratory data which the user can supply, then control returns to MONITOR and the next condition is tried. Otherwise, if there are rules which can be used to evaluate the condition, by virtue of the fact that their actions reference the relevant clinical parameter, they are listed and applied in turn using MONITOR:

12 Start no Retrieve Y = List of Rules which may aid in deducing the value of the PARAMETER Is the PARAMETER a piece of LABORATORY data? yes Ask USER for the Value of the PARAMETER Apply MONITOR to each rule in the List Y RETURN yes Is Value of the PARAMETER known Is Value of the PARAMETER known yes RETURN no Retrieve Y = List of Rules which may aid in deducing the value of the PARAMETER no Ask USER for the Value of the PARAMETER Apply MONITOR to each rule in the List Y RETURN RETURN An example of the kind of reasoning network generated by the MONITOR and FINDOUT mechanisms. Names of the clinical parameters are underlined. When a rule has multiple conditions in the premise, numbers have been included to specify the positions of the associated clinical parameters within the premise condition.

13 GOAL REGIMEN RULE 092 TREATFOR COVERFOR RULE 090 RULE IDENT INFECTLOC FEBRILE SIGNIFICANCE RULE 038 RULE 042 RULE 044 RULE108 SITE SITE COLLECT SIGNUM SITE NUMCLUS NUMPOS RULE 001 SITE RULE 041 RULE SITE SITE ABNORMAL SITE SITE ABNORMAL ASK2 ASK2