What is the primary purpose of acquiring the first image in cisternography over the lower thoracic/lumbar spine?

The primary purpose of acquiring the first image in cisternography over the lower thoracic/lumbar spine is to ensure that the tracer was not infiltrated. This initial imaging captures the distribution of the radiopharmaceutical once it has been administered into the cerebrospinal fluid (CSF) space. If the tracer infiltrates into the surrounding tissues instead of entering the CSF, it can lead to inaccurate results and misinterpretation of the test. By obtaining early images, technologists can confirm that the tracer is where it is supposed to be (within the CSF) and not outside the intended path. This step is crucial for ensuring the reliability of subsequent imaging and, ultimately, the accuracy of the findings related to CSF dynamics and any potential pathological conditions.