54 TABLE 21. Perimeter inp AREA OF Cross SECTIONS OF Bone TakEN FROM DIFFERENT POSITIONS ALONG THE LENGTH OF 1 Human RIB Section number Bone area, cm? Bone perimeter, cm P/A, em/cm? its length, each segment being about 4.5 cm lon tions 100 » thick were eut from each end of the Sternal end 8 9 10 11 13 15 vi 19 20 21 22 0.16 0.18 0.13 0.14 0.11 0.13 0.10 0.13 0.10 0.12 0.13 28 29.3 25.1 24.9 19.4 176 163 193 178 176 16.5 15.2 14.8 15.2 14.0 165 117 148 127 108 25 26 28 0,13 0.14 0.14 0.16 17.3 14.9 15.1 12.8 135.5 106.2 107.8 31 0.16 13.1 30 34 0.16 | a6 38 39 0.17 0.16 0.16 | | 42 0.18 | 43 45 46 49 0.18 0.22 0.21 0.20 50 52 0.20 0.23 53 14.7 14.5 15.] 14.7 14.8 80.6 92.0 85.0 94.4 92.1 82.0 13.3 17.1 16.7 73.8 77.7 79.4 16.4 82 | 16.8 20.0 84 87 0.21 | 19.7 94 55 0.24 | 19.8 82.5 60 0.36 | 63 0.34 66 68 0.27 0.27 56 61 64 72 0.24 0.36 0.33 0.25 19.6 15.5 81.5 43 14.8 41 12.9 38 14.8 18.1 55 67 12.9 21.0 that the rib has been used extensively as a repr tive site for removal of biopsy material in the s bone diseases,7-) the variations noted alongits would appear to be of considerable interest. The sixth rib was first cut into seven segment 39 84 ments. These were x-rayed using a high contrast film so that the bone appeared clear on a black ground. This type of microradtograph (as opp: the more conventional type which shows d: shades of gray corresponding to different minera! ties) greatly facilitated the definition of bone si for quantitation of bone area and surface lengt! the automatic scanner. The scanning device!y same as that used previously.‘* 7 The bone : length and the bone area were determined fre number and length of line segments generated ov bone which appeared as the clear portion on the. full description of the method is given elsewher Figure 48 demonstrates the appearance of radiographs of the cross sections of bone taken junction of each of the 7 segments. It is interest note that close to the costal cartilage junction, tl tex is very thin and this encloses a large num very fine trabeculations. About 5 cm from the vei end the cortex is very much thicker and the trab tions are fewer and coarser. Values for the cro: tional area, together with the surface length or p: ter of each of the bone sections studied, are gic Table 21. Values of perimeter/area are also Values for the representative bone sections tak 4.5¢m intervals are also shown in Figure 49. In 21 the numbers of the sections listed start with mi 1 taken from the sternal end of the rib and rai number 72 taken from the vertebral end. The bon changes from 0.10 cm? to 0.36 cm?, while the peri changes from 12.9em to 29cm. The bone ai greatest about 5em from the vertebral end wher cortex is thickest. The perimeter is small at this giving a value of 43 cm/cm? for perimeter/area (: compared with a value about 5 times greater obt for a section taken close to the sternal end. CONCLUSION bone-seeking isotopes such as °®Pu and *44Am deposit specifically on bone surfaces. Calculations of the relative toxicity of these isotopes compared with those which deposit throughout the whole volume of bone (such as 7°°Ra) must inelude a factor for the surface/ volume ratio. As part of this study, which was designed to make representative sampling throughout the whole skeleton, a single rib of a cadaver was studied at 40 different positions along its length. In view of the fact The variation both in the thickness of the corte: in the size and numberof the trabeculations at diff positions along the length of a single rib underlin need for caution in comparing biopsy material t from different subjects. In particular, biopsy sar: taken at positions as close as 1em apart have shown to vary by as much as 15%. This could easily Jead to an erroneous diagnosis of osteoporo: a normal subject if extreme care is not taken to e