Final answer:
In medical imaging, ultrasonography is the least sensitive but most specific evaluation for fetal viability. For cell viability assays outside of pregnancy, measuring lactate dehydrogenase (LDH) release is a specific method for detecting cell death and assessing cytotoxicity.
Step-by-step explanation:
The least sensitive but most specific evaluation for viability can refer to different contexts. In the case of medical imaging during pregnancy, ultrasonography is the least invasive and therefore the most suitable for this sensitive situation. It is highly specific for evaluating various aspects of fetal development such as growth, structure, and blood flow, while avoiding the potential risks associated with more invasive procedures like CT scans or PET scans. Moreover, ultrasound is extensively used because it provides real-time images, does not involve radiation, and has a long history of safety if performed by a trained operator.
In another context, determining cell viability, an assay using lactate dehydrogenase (LDH) release is a technique that can detect cell death due to the loss of plasma membrane integrity with high specificity. The level of LDH enzyme released into the medium reflects the degree of cytotoxicity, and the assay measures cell viability accurately without being overly sensitive to non-specific factors.