Fig 1.
The illustration of calcaneal-fifth metatarsal angle (CA–MT5 angle) α.
Diagram of the lateral radiographic images of a participant, which illustrates that the calcaneal-fifth metatarsal angle (CA–MT5 angle) α, also called the arch angle, is defined by lines at the calcaneus and fifth metatarsal. In Taiwan, the criteria for new military conscripts include that individuals are required to serve mandatory service if they have an arch angle <165°, substitute service if they have an angle between 165° to 168°, and are exempt from military service if their arch angle >168°.
Fig 2.
Lateral radiographic image of a participant.
(A) The original radiographic image. The reference images of the calcaneus (B) and the fifth metatarsal bone (C) isolated from (A).
Fig 3.
Template images of the calcaneus.
The images were classified into four different groups (A, B, C and D).
Fig 4.
Flowchart of the methodology of the mutual information (MI) registration algorithm.
The images were converted into two-dimensional image parameters (θ, tx, ty). Image registration was achieved after repeated calculation until the MI between the template and the reference images was maximized.
Fig 5.
Process of CA–MT5 angle measurement for subject 31 using the MI registration algorithm.
(A) Lateral radiographic image of the subject. (B) Reference images of the two critical bones were manually isolated. (C) Generation of the template images (lower edges to be horizontal) and classification (classified as Group C in this case). (D) MI image registration to obtain the angles of inclination of these two bones.
Table 1.
Comparison of the CA-MT5 angle measurements obtained by radiologists A and B and using the MI registration algorithm.
Table 2.
Comparison of the difference in the CA-MT5 angle among radiologists A, B, and the MI registration algorithm.
Fig 6.
Receiver operating characteristic (ROC) curves of different measurements.
(A) ROC curves of radiologist B and MI registration when the measurement of radiologist A was used as the standard. (B) ROC curves of radiologist A and MI registration when the measurement of radiologist B was used as the standard.
Fig 7.
Bland–Altman plot (B-A plot) used to assess the agreement between two measurement methods.
(A) Radiologist A vs. MI. (B) Radiologist B vs. MI. The X-axis is the average of the measurements, and the y-axis is the difference between the two methods.