For example, it has been estimated that if we were to use sections of about 35 square micrometers (millionths of a meter) at a thickness of 20 nanometers, we would need more than 1.4 billion sections to reconstruct fully just one cubic millimeter of tissue. So, while complete reconstructions of a small region of the mammalian brain are feasible, structures like the cerebral cortex – with a surface area of 0.22 square meters and a thickness of between 1.5-4.5 millimeters – cannot be fully reconstructed.
比如，据估计，如果我们使用厚20纳米、面积35平方微米（一米的一百万分之一）的截面，我们就需要14多亿个截面来完整构造一立方毫米的组织。因此，尽管完全重建哺乳动物大脑的一小片区域是可行的，但像大脑皮层这样的结构——表面积0.22平方米，厚度在1.5—4.5毫米之间——是无法完整重建的。