title: Parallel definition of tear film maps on distributed-memory clusters for the support of dry eye diagnosis.
abstract: OBJECTIVE
  The analysis of the interference patterns on the tear film lipid layer is a useful clinical test to diagnose dry eye syndrome. This task can be automated with a high degree of accuracy by means of the use of tear film maps. However, the time required by the existing applications to generate them prevents a wider acceptance of this method by medical experts. Multithreading has been previously successfully employed by the authors to accelerate the tear film map definition on multicore single-node machines. In this work, we propose a hybrid message-passing and multithreading parallel approach that further accelerates the generation of tear film maps by exploiting the computational capabilities of distributed-memory systems such as multicore clusters and supercomputers.
  
  
  METHODS
  The algorithm for drawing tear film maps is parallelized using Message Passing Interface (MPI) for inter-node communications and the multithreading support available in the C++11 standard for intra-node parallelization. The original algorithm is modified to reduce the communications and increase the scalability.
  
  
  RESULTS
  The hybrid method has been tested on 32 nodes of an Intel cluster (with two 12-core Haswell 2680v3 processors per node) using 50 representative images. Results show that maximum runtime is reduced from almost two minutes using the previous only-multithreaded approach to less than ten seconds using the hybrid method.
  
  
  CONCLUSIONS
  The hybrid MPI/multithreaded implementation can be used by medical experts to obtain tear film maps in only a few seconds, which will significantly accelerate and facilitate the diagnosis of the dry eye syndrome.
authors.affiliation: Grupo de Arquitectura de Computadores, Universidade da Coruña, Campus de Elviña s/n, 15071 A Coruña, Spain. Electronic address: jgonzalezd@udc.es.
authors.forename: Jorge
authors.initials: J
authors.lastname: González-Domínguez
authors.affiliation: INESC TEC-INESC Technology and Science, Campus da FEUP, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Remeseiro
authors.affiliation: Grupo de Arquitectura de Computadores, Universidade da Coruña, Campus de Elviña s/n, 15071 A Coruña, Spain.
authors.forename: María J
authors.initials: MJ
authors.lastname: Martín
mesh_terms: D000465:Algorithms; D015352:Dry Eye Syndromes / Q000175:diagnosis*; D006801:Humans; D013666:Tears
keywords: Dry eye syndrome; High performance computing; Message passing; Parallel programming; Tear film map