THE CULTIVATION OF CELLS IN 3D HAS GAINED MORE INTEREST IN RESEARCH ONCE 3D ARCHITECTURE
CAN BE CLOSER TO FULL CELL PHYSIOLOGICAL FUNCTIONALITY. THE CELL CULTURE IN A SPHEROID FORMAT
HAS SHOWN VERY PROMISING RESULTS, FURTHER FOR BIOPRINTING DEVELOPING SO FAST DURING THE
LAST DECADE. THE INTERACTION OF SPHEROIDS AND THE MATRIX, OR BIOINK, HAVE PROPORTIONATE
NEW STRUCTURES TO BE ANALYZED, ESPECIALLY IF ONE WOULD LIKE TO FOLLOW THE WHOLE SYSTEM
(SPHEROID AND BIOINK) WITHOUT FLUORESCENT DYES. IN THIS PAPER, WE PRESENT A NON-
DESTRUCTIVE IMAGE ANALYSIS OF THE SPHEROID VIABILITY CONSIDERING THREE DIFFERENT IMAGE
DATASETS OF FIBROBLAST NIH-3T3 SPHEROIDS ACQUIRED IN DIFFERENT CULTURE CONDITIONS, EACH
CONSISTING OF APPROXIMATELY 300 CELL SAMPLES. THE FIRST TWO SETS POSSESS FOUR POSSIBLE
CELLULAR STRUCTURES: LIVING CELLS INSIDE SPHEROIDS (THE LARGEST CELL AGGREGATE IS THE
SPHEROID; IT COMPRISES CELLS WITH LOWER BRIGHTNESS VALUES AND A VERY WELL DEFINED
MEMBRANE WITH A DOT PLACED AT ITS CENTER, CHARACTERIZING ITS NUCLEUS); LIVING CELLS
OUTSIDE SPHEROIDS (CELLS CHARACTERIZED BY THEIR LOWER BRIGHTNESS VALUES, VERY WELL-
DEFINED BOUNDARIES, THE CELL MEMBRANE, AND EASY IDENTIFICATION OF THE NUCLEUS, WHICH
LOOKS LIKE A DOT IN THE CENTER OF THE CELL; THOSE CELLS ARE FOUND IN THE AGGREGATES); DEAD
CELLS (SINGLE-CELL, CHARACTERIZED BY HIGH BRIGHTNESS AND VERY LIGHT CENTRAL FORMATION,
IDENTIFIES AS THE CELL NUCLEUS); AND BACKGROUND (WELL PLATE AREA, NO CELL STRUCTURE IS
IDENTIFIED), WHILE THE THIRD SET CONSISTS ONLY OF LIVING CELLS INSIDE THE SPHEROID AND
BACKGROUND. EACH DATASET WAS SAMPLED WITH A PROPORTION OF 70%-20%-10% FOR
TRAINING-TESTING-VALIDATION DATASETS. IN ORDER TO IMPROVE THE CLASSIFICATION TASK AND AVOID
OVERFITTING, I.E., THE LACK OF GENERALIZATION OF THE NETWORK, SEVERAL STRATEGIES WERE
APPLIED, SUCH ADDING BLURRED IMAGES TO THE TRAINING DATASET. THE CNN ARCHITECTURES
CHOSEN WERE WIDE RESNET, VGG16 WITH BATCH NORMALIZATION, SQUEEZENET, RESNET,
MOBILENETV3 LARGE, GOOGLENET AND ALEXNET, EACH PRESENTING A DIFFERENT TECHNOLOGY
FOR THE CONVOLUTIONAL LAYER (RESPONSIBLE FOR EXTRACTING THE RELEVANT FEATURES FROM THE
IMAGES) AND THE CLASSIFICATION LAYER (RESPONSIBLE FOR ACTUALLY CLASSIFYING EACH IMAGE
ACCORDING TO THE FEATURES EXTRACTED FROM THE CONVOLUTIONAL LAYER) AS WELL. VGG16
PRESENTED THE HIGHEST F1-SCORE: THE HARMONIC AVERAGE OF THE PRECISION, THE RELATION
BETWEEN TRUE POSITIVES AND FALSE POSITIVES, AND RECALL, THE RELATION BETWEEN TRUE
POSITIVES AND FALSE NEGATIVES, WITH MEAN VALUE OF 0.97. WITH THE RESULTS ACHIEVED, THE
AUTHORS BELIEVE THAT USING CNNS FOR CELL CLASSIFICATION IS A PROMISING TOOL FOR AUTOMATING
THIS TASK, THUS, THE NEXT STEP OF THE PRESENTED WORK IS TO USE VGG16 AS A BACKBONE FOR
IMPLEMENTING A NEURAL NETWORK THAT CAN AUTOMATE THE IDENTIFICATION AND CELL COUNTING IN
A SPHEROID IMAGE.