Image acquisition
It may be appropriate for good research on muscle to work with a number greater than 400 fibres [10]. In the current study, this number is reached using x200 magnification with at least two fields for each type of coloration. The number of fields increase with age, this latter was respectively, 2 at the post hatching, D7 and D14, 3 fields at D21, 4 fields at D28, more than 6 fields at D35, J42, J49 and J56, which inevitably require more time for taking the serial images. This problem forced researchers to minimize the number of fields as well as the number of fibres to be analysed [3, 4]; or to use different magnifications in the same study with high magnifications for muscles of early ages and low magnifications for muscles of adults [11]. This last author conducted a study on muscles of developing chicken from D0 post hatching until the age of 55 weeks and analysed an average of 400 fibres in two microscopic fields with different magnifications (x45, x90, and x215). However, most researches have not specified the magnification used and / or the number of fibres analysed [24, 26, 28, 29, 31, 35–38,]. In our study, the average number of fibres by image at the early ages, D0, D7 and D14 post hatching is 950, 227 and 253, respectively, which considered acceptable. However, the segmentation of these images was very difficult as result of fibres’ small size despite the acceptable resolution of the camera (18 MP). Similarly, same observations were produced using the magnification x250. The images of x100 magnification are more adequate regarding the average number of fibres / image, which exceeds 400 fibres at D7, J14, J21 and J28, and 200 fibres at D35, J42, J49 and J56; although the segmentation was very difficult especially at the early ages D7, D 14 and D21, where the images become blurred when the zoom was applied to recognize boundaries of the cells. In addition, it is impossible to work on images using this magnification at D0 post hatching.
The magnification of x400 is more laborious due to the number of fields that exceeds 6 for each muscle studied from the day 7 of post hatching.
The average number of fibres / image in all the ages studied varies between 600 and 1000 using CytoF, which considered very acceptable. This related to the software used by this group, which can work on images in SVS format. In addition, the capacity of segmentation of this later arrive the whole virtual section but more expensive.
Time required for segmentation comparison between the three software (CytoF, Fiji «FDP, FM» and IP)
Image analysis algorithms are widely used by biomedical researchers and software engineers. To carry out this part of the work, firstly, we selected two semi-automatic software which are ImageJ (Fiji) from NIH and IP, from Media Cybernetics since these two software are the most popular currently according to Kostraminova et al. [6] and their popularity in research field associated to several factors such as, accuracy of results, accessibility (price and availability). Secondly, we worked with the group Cytoinformatics LLC for segmentation with automatic software. The comparison between the three software was conducted based on:
The time required for segmentation and the number of fibres obtained
The observation of the time of segmentation of the nine images by the three software reveals that this time decreases with age but it is fluctuating from one image to another and that could be explained
Firstly, by the degree of automatism the tool used for segmentation:
The total time required for segmentation, in hours: minutes: seconds, of the nine images by Fiji/M using the computer mouse is 26: 23:37 and their average segmentation time is 02: 56: 25; so in our unpublished work which was carried out on four muscles with 10 repetitions for nine ages studied, we needed 1061.6 hours to complete this segmentation which is the equivalent of 44.33 days of non-stop work or almost 353.23 days with 8 hours of work per day (Fig. 6).
To segment these images by the same software with the use of FDP this time is the highest compared to the other segmentation methods which is 27: 24: 56, therefore an average segmentation time of 3: 05: 00, but it remains the closest to measuring the fibre parameters.
The total time required for the segmentation of these same nine images by IP is 10:21:35 and their average segmentation time is 1:13:06; so for our work it took 438.6 hours which is the equivalent of 18.27 days of non-stop work or almost 146.2 days with 8 hours of work (Fig. 6).
On the other hand, the new image processing algorithms can manage an automatic segmentation of the image in less than a minute [4, 23] even if these images have a large scale which can reach up to 9000 × 9000 [23] which considerably reduces the average image processing time.
Secondarily, this time is also influenced by the number of fibres / image which linked to several factors such as:
Age: the number of fibres / image decreases progressively with age due to the radial growth of the fibre and therefore the segmentation time is negatively correlated with age.
The shape and size of the fibre: the irregular and overlapping shape as well as the small size of the fibre increase the segmentation time; these same findings are observed by Liu et al. [4], and Wang [29].
The percentage of connective tissue: when the connective tissue is abundant in the image, the number of fibres and overlapped ones decrease, which reduce the time of segmentation. The percentage of connective tissue varies within the same muscle and from one muscle to another; it has decreasing value of the slow ◊ intermediate ◊ rapid, according to our unpublished work. As an example, the images chosen at ages D21 and D28 which contain a lot of connective tissue and the number did not exceed 420 fibres, presented a segmentation time lower than the other images ( Fig. 6 and Table 2).
Finely, by the image quality: the well-coloured image with good resolution and less debris and artefacts has a low segmentation time.
The time required for post processing of segmented images
The performance of image processing software for muscle tissue is linked to its ability to remove artefacts, irrelevant tissue and to separate any contact between the fibres. The average time (in hour: minute: second) of the post processing of the nine images segmented by FDP and FM was around 00: 25: 00 (Fig. 7) and therefore a total time for the post processing of all the images of our work which is around 112: 50: 00.
The average time of post processing of the nine images segmented by CytoF which was carried out by Fiji is 0: 10: 16 h (Fig. 7) and therefore a total average time for the post-processing of all the images of our work which is estimated at 45: 72: 00 h. The post-processing time of the segmented images by CytoF is very low because these images do not contain artefacts and irrelevant tissues and this time is intended only for the segmentation of the touching fibres, in addition the average time of the post-processing of these same images by Image Pro Plus 10 (IP) is the highest compared to the previous software with a time of 00: 32: 06 h (Fig. 7) and therefore a total time which is by means of 144: 45: 00 h, this is due the presence of many artefacts and irrelevant tissue in the images segmented with this software (Fig. 8).
Comparison of muscle fibre parameters obtained after segmentation with the three software
The three segmentation methods FDP, FM and CytoF gave more consistent results for CSA with non-significant differences for the average surface area which is less than 3.34% for CytoF compared to FDP (Table 3), this parameter (the Area) which is the main criterion for studying muscle fibre confirms that the measurements obtained by CytoF concerning CSA are closer to the measurements obtained by manual segmentation performed by FDP and FM. No significant difference between FDP and FM.
However, statistically, there are highly significant differences for the Perimeter and DMF between CytoF and FDP but the differences are not large (Table 3) with fairly encouraging percentages for these two parameters calculated by the CytoF (less than 5.06% and 5.01% for the Perimeter and DMF respectively) compared to those calculated by FDP.
According to Kostraminova et al. [6], Image J (Fiji) and IP are widely accepted for precise measurements of CSA. The highly significant difference between FDP and IP regarding the average area of the fibre is related to the thresholding step of IP, which leaves in some cases a small margin (Fig. 9). This influence the calculation of average value which is less than 5.02% compared to that calculated by FDP and which remains very satisfactory.
The highly significant differences between FDP and IP concerning the perimeter and MFD are associated to fibre Area calculation (less Area = less perimeter and less MFD). The MFD is very robust against experimental errors such as the orientation of the angle of section [4], and it is recommended by Markus et al. [16]. However, it is influenced by the segmentation technic because it measures the minor diameter in the muscle cell [38]. Despite this, the average values calculated by IP of these two parameters (Perimeter and MFD) are also acceptable, they are less than 7.19% and 3.96% respectively compared to those found by FDP.
Semi-automatic tools (Fiji and IP), always require prior processing, where the operator must interact manually with the computer, using a digitizing pen or a computer mouse, to remove artefacts and irrelevant tissue and trace the contours of unsegmented muscle fibres. This interaction makes the analysis of a large number of images more laborious and impractical, these observations are confirmed by some authors [23, 30, 39]; despite that, this software remain used by a large community of researchers.
For automatic tools and despite their expensive prices and availability, in addition to the critics addressed to many of these programs such as the use of shortcuts (assuming for example that the fibres are circles or ellipses) which can make the measurements of the morphological parameters of the fibres inaccurate [39]; the software of the CytoF remain far from these criticisms and gives satisfactory results.
We adopted the manual method for typing muscle fibres for two reasons; the first is the additional costs and the second is the difficulties of classifying all muscle cells, especially in sections where the muscle fibres are not parallel to each other or they change shape through a large series of sections, or if certain fibres disappear from the section or divide; these cases are well presented in our work and proved by Karen et al. [28].