This circumstance, termed patient prosthesis mismatch, is associ- ated with a high transvalvular gradient, per- sistent LV hypertrophy, and an increased rate of cardiac events after valve replacement.10,11 Diagnosis in the setting of bileaflet mechanical valves is complicated by nonlaminar patterns of blood flow, for which significant pressure recovery may be present; thus, a high velocity in the central narrow slit-like orifice may not cor- relate with prosthetic valve stenosis or patient prosthesis mismatch. Prosthetic valve stenosis is distinguished from patient prosthesis mismatch by comparison with the early postoperative base- line study and by visualization of the appearance and motion of the valve leaflets. Prosthetic valve stenosis is characterized by a clinical course of progressive increase in transvalvular velocity and pressure gradient in conjunction with abnormal thickened/calcified leaflets (for bioprosthetic valves) or evidence of pannus formation (with mechanical valves). 2. The motion of the leaflets of a mechanical valve is best evaluated radiographically with fluoros- copy or cine-CT imaging because strong reflec- tions from the mechanical valve obscure motion on echocardiographic imaging in most patients, particularly as assessed on images from the trans- thoracic approach. With fluoroscopic imaging, the angle of imaging must be adjusted to dem- onstrate leaflet motion from a side view, permit- ting measurement of the angles of opening and closure that can be compared with expected values for that valve type. Cine-CT images are obtained at a high frame rate focused on the prosthetic valve in a 3D acquisition. Compared with fluoroscopy, cine-CT 3D images are less operator dependent for measuring opening and closing angles. In addition, cine-CT allows detection of pannus or thrombus on or adjacent Table 23. 