![]() ![]() Combined effect of 90° and 180° pulses on the flowing spins.Partial saturation of the imaged slab by repetitive short TR pulses.Increase in flowing spin phases as they pass into an imaged slab.The other choices are all spin-phase effects. High intravascular signal in an entry slice (choice a) is a type of TOF known as flow-related enhancement. Time-of-flight (TOF) effects refer to signal variations resulting from the motion of protons flowing into or out of an imaging volume during a given pulse sequence. High signal in a vessel due to gradient moment nulling.Signal loss due to turbulent flow in an aneurysm.Signal loss due to in-plane flow within an imaging gradient.High intravascular signal in an entry slice.Which one of the following flow-related phenomena is considered a time-of-flight (TOF) effect?.The probability of turbulent flow is proportional to the Reynolds number (Re), being directly proportional to blood velocity and vessel diameter, and inversely proportional to blood viscosity. In the stump of a newly occluded vessel.In a vessel with elevated blood viscosity.In a vessel with rapid blood velocities.In which situation would you be more likely to see turbulent flow?.Values of Re less than 2000 predict that flow will be laminar, whereas values greater than 2500 usually indicate that flow will be turbulent. The Reynolds number (Re) is a dimensionless parameter used to predict flow characteristics in ideal fluids. Values of Re 2500 predict laminar flow.Which statement about the Reynolds number (Re) in ideal fluids is true?.They are less likely in the distal thoracic aorta, so the correct answer is (c). ![]() ![]() Vortex flow is prominent in the ascending aorta, as jets of blood are expelled and swirl around during each cardiac contraction. Such vortices, also called flow eddies, frequently occur at vascular bifurcations and distal to areas of stenosis. Vortex flow refers to localized swirling or stagnant blood flow that has separated from the central streamlines within a vessel. In which anatomic situation would you not expect to find vortex flow?.Theoretically, the distribution of velocities in a perfectly straight, nonbranching vessel with nonpulsatile flow should be parabolic in cross-section. Laminar flow refers to a predictable distribution of flow velocities in layers (lamina) that parallel the vessel wall. In ideal laminar flow the distribution of velocities in cross-section across a vessel should be.In extremely high-grade stenosis, however, vascular resistance becomes so high that the flow rates and velocities fall just before total occlusion is reached. What happens to peak velocities as a vessel goes becomes increasingly stenotic?Īs vessels become increasingly stenotic their peak velocities initially increase (due to the Bernoulli effect).Flow in the distal aorta and iliac vessels slows to the 100-150 range, whereas peak velocities in the proximal carotid, brachial, and superficial femoral arteries are about 80-110 cm/sec. The ascending aorta has the highest average peak velocities of the major vessels typical values are 150-175 cm/sec. Which blood vessel has the greatest peak velocity?.The brain and kidneys have low vascular resistance thus, carotid and renal arterial vessels demonstrate high forward flows even during diastole. The thoracic aorta has prominent reversal of flow during diastole as the coronary circulation is filled. Which blood vessel normally demonstrates a prominent reversal of flow during the cardiac cycle?.Centrally within the lumen, blood flow will be most rapid. Near the vessel wall where fluidic shearing and frictional forces are greatest, the blood flow will be nearly zero. The blood flow is the same across the entire vessel.In what part of a vessel is the blood flow the slowest?.So the bulk blood flow (Q) = V x A = 50 cm/sec x 3.14 cm² = 157 cm³/s. The cross-sectional area (A) of the vessel is πr² = π (1 cm)² = 3.14 cm². What is the approximate bulk blood flow (Q) passing through a 2 cm diameter artery where the average velocity is 50 cm/s?.Bulk blood flow (Q) through a certain point in the vascular tree within a given period of time is measured in what units?īulk flow is a volume per unit time and is expressed in units of cm³/s. ![]()
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