A given weight of tissue or tumor may be needed to perform an analysis. Needle biopsy can often deliver a core of tissue with minimal invasion. A quick estimate of weight can be made from the size of the needle used and the length of the tissue core.
While the core can always be weighed, a sensitive scale may not be readily available. Handling of small tissue fragments can result in contamination or drying out. Therefore, a quick estimate of specimen adequacy is desirable.
Parameters:
(1) inner diameter of the needle = diameter of core
(2) length of the core
(3) density of the tissue
volume of the core in mL =
= (((diameter of core in cm) / 2)^2) * PI() * (length in cm)
weight in milligrams =
= (volume in mL) * (density in grams/mL) * 1000
volume of core in mL to obtain a weight in milligrams =
= (weight in mg) / ((density) * 1000)
length of core in cm to obtain a weight in milligrams =
= (weight in mg) * 4 / ((density) * 1000 * PI() * (((diameter in cm) / 2)^2))
Needles are selected based on their gauge which usually is based on external diameter. The inner diameter may vary between manufacturers.
|
Gauge |
Inner Diameter in mm |
|
10 |
2.69 |
|
11 |
2.39 |
|
12 |
2.16 |
|
13 |
1.80 |
|
14 |
1.60 |
|
15 |
1.37 |
|
16 |
1.19 |
|
17 |
1.07 |
|
18 |
0.84 |
|
19 |
0.69 |
|
20 |
0.58 |
|
21 |
0.50 |
|
22 |
0.39 |
|
23 |
0.32 |
|
24 |
0.29 |
|
25 |
0.24 |
If this data is analyzed in the Minitab the following estimate for diameter is obtained.
diameter in mm =
= (0.009625 * ((gauge)^2)) - (0.4992 * (gauge)) + 6.716
diameter in cm = (diameter in mm) / 10 =
= (0.0009625 * ((gauge)^2)) - (0.04992 * (gauge)) + 0.6716
|
Tissue |
Density at Body Temperature |
|
lung |
0.33 g/mL |
|
fat |
0.900 g/mL |
|
water |
0.994 g/mL |
|
myocardium, liver |
1.053 g/mL |
|
fat-free mass in an adolescent |
1.096 g/mL |
|
red blood cell |
1.097 g/mL |
|
pure protein |
1.34 g/mL |
|
bone mineral |
2.982 g/mL |
The default density for the implementation will be 1.053. The actual density may differ if there is fatty infiltration, fibrosis or tissue deposits.
Specialty: Clinical Laboratory
ICD-10: ,
