Read the following text to answer question 23.
The Alzheimer’s mystery
By Patrick J. Skerrett
Alzheimer‘s disease, which begins years, even decades, before it causes symptoms, is a quietly ticking time bomb. But until recently doctors had no diagnostic test that could ―hear‖ the ticking. Unfortunately, it didn‘t matter much that Alzheimer‘s couldn‘t be spotted early – at a stage called Mild Cognitive Impairment, or MCI – since there were no treatments. Today, however, there are new diagnostic tests that can detect Alzheimer‘s at an early stage, and several disease-modifying drugs are in advanced clinical trials.
The brain shrinkage caused by Alzheimer‘s can now be measured with Volumetric Magnetic Resonance Imaging (MRI). This technique takes a series of MRI brain scans and then uses sophisticated mathematical models to analyze the results. Most important, volumetric MRI enables researchers to identify subtle shrinkage in brain areas first affected by Alzheimer‘s, such as the hippocampus, which is involved in memory.
Another technology in limited clinical use is Fluorodeoxyglucose Positron Emission Tomography (FDG-PET). Images produced by FDG-PET reveal patterns of glucose metabolism in the cerebral cortex, the site of abstract thought, reasoning and learning. Because active neurons guzzle glucose for energy, diminished uptake in a specific pattern can denote Alzheimer‘s. In the research setting, scientists have even used FDG-PET to identify people who do not yet have Alzheimer‘s but are at risk for developing it, or for developing mild cognitive impairment.
Newsweek. Vol. CLI. January 21, 2008. p. 64 (Adapted).
Considering meaning and standard English, in the text above the sentence “But until recently doctors had no diagnostic test that could 'hear' the ticking” can be substituted by any of the following, EXCEPT:
