pyConTextNLP

pyConTextNLP is a Python implementation/extension/modification of the ConText algorithm described in CITE which is itself a generalization of the NegEx algorithm described in CITE.

The package is maintained by Brian Chapman at the University of Utah. Other active and past developers include:

• Wendy W. Chapman
• Glenn Dayton
• Danielle Mowery

Introduction

pyConTextNLP is a partial implementation of the ConText algorithm using Python. The original description of pyConTextNLP was provided in Chapman BE, Lee S, Kang HP, Chapman WW, "Document-level classification of CT pulmonary angiography reports based on an extension of the ConText algorithm." J Biomed Inform. 2011 Oct;44(5):728-37

Other publications/presentations based on pyConText include:

• Wilson RA, et al. "Automated ancillary cancer history classification for mesothelioma patients from free-text clinical reports." J Pathol Inform. 2010 Oct 11;1:24.
• Chapman BE, Lee S, Kang HP, Chapman WW. Using ConText to Identify Candidate Pulmonary Embolism Subjects Based on Dictated Radiology Reports. (Presented at AMIA Clinical Research Informatics Summit 2011)
• Wilson RA, Chapman WW, DeFries SJ, Becich MJ, Chapman BE. Identifying History of Ancillary Cancers in Mesothelioma Patients from Free-Text Clinical Reports. (Presented at AMIA 2010).

Note: we changed the package name from pyConText to pyConTextNLP because of a name conflict on pypi.

Installation

pyConTextNLP can be downloaded from the Downloads page here on the negex Google Code project. Alternatively, it can be downloaded from the pypi repository http://pypi.python.org/pypi/pyConTextNLP. Since pyConTextNLP is registered with pypi, it can be installed with easy_install or pip:

easy_install pyConTextNLP pip install pyConTextNLP

The only listed dependency is NetworkX and easy_install should also install this for you, if it is not already installed. However, there is optional functionality that is dependent on pygraphviz. I do not yet have this worked into the setuptools script.

Code Structure

The code has been modified substantially since the code base used for the JBI publication. In the current version, pyConTextNLP corresponds to pyConTextGraph in previous versions. This code uses [http://networkx.lanl.gov/ NetworkX] to structure the relationship between targets and modifiers in the markup.

The package has three files:

• itemData.py. This is where the essential domain knowledge is stored in 4-tuples as described in the paper. For a new application, this is where the user will encapsulate the domain knowledge for their application.
• pyConTextGraph.py. This module defines the algorithm
• pyConTextSql.py.

How to Use

I am working on improving the documentation and (hopefully) adding some testing to the code.

Some preliminary comments:

• pyConTextNLP works marks up text on a sentence by sentence level.
• pyConTextNLP facilitates reasoning from multi-sentence documents, but the markup (e.g. negation is all limited within the scope of a sentence.
• pyConTextNLP assumes the sentence is a string not a list of words

The Skeleton of an Example

To illustrate how to use pyConTextNLP, i've taken some code excerpts from a simple application that was written to identify critical finders in radiology reports.

The first step in building an application is to define itemData objects for your problem. The package contains itemData objects defined in pyConTextNLP.pyConTextGraph.itemData. Common negation terms, conjunctions, pseudo-negations, etc. are defined in here. An itemData instance consists of a 4-tuple. Here is an excerpt

probableNegations = itemData(
["can rule out","PROBABLE_NEGATED_EXISTENCE","","forward"],
["cannot be excluded","PROBABLE_NEGATED_EXISTENCE",r"""cannot\sbe\s((entirely|completely)\s)?(excluded|ruled out)""","backward"])

The four parts are

1. The literal "can rule out", "cannot be excluded"
2. The Category "PROBABLE_NEGATED_EXISTENCE"
3. An optional regular expression used to capture the literal in the text. If no regular expression is provided, a regular expression is generated literally from the literal.
4. An optional rule. If the itemData is being used as a modifier, the rule states what direction the modifier operates in the sentence: current valid values are: "forward", the item can modify objects following it in the sentence; "backward", the item can modify objects preceding it in the sentence; or "bidirectional", the item can modify objects preceding and following it in the sentence.

For the criticalFinderGraph.py application, we defined itemData for the critical findings we wanted to identify in the text, for example pulmonary emboli and aortic dissections. These new itemData objects were defined in a file named critfindingItemData.py

critItems = itemData(
['pulmonary embolism','PULMONARY_EMBOLISM',r'''pulmonary\s(artery )?(embol[a-z]+)''',''],
['pe','PULMONARY_EMBOLISM',r'''\bpe\b''',''],
['embolism','PULMONARY_EMBOLISM',r'''\b(emboli|embolism|embolus)\b''',''],
['aortic dissection','AORTIC_DISSECTION','',''])

We also added negation terms that were not originally defined in pyConTextNLP:

definiteNegations.prepend([["nor","DEFINITE_NEGATED_EXISTENCE","","forward"],])

Once we have all our itemData defined, we're now ready to start processing text.

In our application we need to import the relevant modules from pyConTextNLP as well as our own itemData definitions:

import pyConTextNLP.pyConTextGraph.pyConTextGraph as pyConText
import pyConText.helpers as helpers
from critfindingItemData import *

Assuming we have read in our documents to process and that the basic document unit is a report we can write a simple function to process the report

    def analyzeReport(report, targets, modifiers ):
        """given an individual radiology report, markup the report based on targets and modifiers"""
        # create the pyConText instance
        context = pyConText.pyConText()

        # split the report into individual sentences. Note this is a very simple sentence splitter. You probably
        # want to write your own or use a sentence splitter from nltk or the like.
        sentences = helpers.sentenceSplitter(report)

        # process each sentence in the report
        for s in sentences:
            context.setTxt(s)
            context.markItems(modifiers, mode="modifier")
            context.markItems(targets, mode="target")

            # some itemData are subsets of larger itemData instances. At the point they will have all been
            # marked. Drop any marked targets and modifiers that are a proper subset of another marked
            # target or modifier
            context.pruneMarks()

            # drop any marks that have the CATEGORY "Exclusion"; these are phrases we want to ignore.
            context.dropMarks('Exclusion')

            # match modifiers to targets
            context.applyModifiers()

            # Drop any modifiers that didn't get hooked up with a target
            context.dropInactiveModifiers()

            # put the current markup into an "archive". The archive will later be used to reason across the entire report.


        return context

The markup is stored as a directed graph, so determining whether a target is, for example, negated, you simply check to see if an immediate predecessor of the target node is a negation. This is all done with NetworkX commands.

To access the underlying graph from the context object evoke the getCurrentGraph() method

g = context.getCurrentGraph()

Here is some code to get a list of all the target nodes in the markup:

targets = [n[0] for n in g.nodes(data = True) if n[1].get("category","") == 'target']

Here is a function to test whether a node is modified by any of the categories in a list

def modifies(g,n,modifiers):
    """g: directed graph representing the ConText markup
        n: a node in g
        modifiers: a list of categories e.g. ["definite_negated_existence","probable_existence"]
        modifies() tests whether n is modified by an objects with category in categories"""
    pred = g.predecessors(n)
    if( not pred ):
        return False
    pcats = [n.getCategory().lower() for n in pred]
    return bool(set(pcats).intersection([m.lower() for m in modifiers]))