Contrast medium is given intravenously to assess myocardial perfusion and LGE. It can also detect regions of myocardial infarction by showing areas of decreased resting perfusion. Ischemia can be partial (poor perfusion) or total. Atherosclerosis narrows blood vessels in the brain, resulting in decreased cerebral perfusion. In contrast, the word "ischemia" refers solely to the lack of blood (poor perfusion). Treatment of HHS begins with reestablishing tissue perfusion using intravenous fluids. People with hypovolemic shock have severe hypovolemia with decreased peripheral perfusion. Abnormal development of the placenta leads to poor placental perfusion. The regulation of tissue perfusion occurs in microcirculation. Physiologic dead space cannot change as it is ventilation without perfusion. Malperfusion can refer to any type of incorrect perfusion though it usually refers to hypoperfusion. In those with poor tissue perfusion, boluses of isotonic crystalloid solution should be given. The redundancies that the circle of Willis introduce can also lead to reduced cerebral perfusion. It is commonly used for lung perfusion scanning. The overall effect is an insufficient blood perfusion in the upper part of the body.