Utility of SPECT Functional Neuroimaging of Pain

Abstract

Functional neuroimaging modalities vary in spatial and temporal resolution. One major limitation of most functional neuroimaging modalities is that only neural activation taking place inside the scanner can be imaged. This limitation makes functional neuroimaging in many clinical scenarios extremely difficult or impossible. The most commonly used radiopharmaceutical in Single Photon Emission Tomography (SPECT) functional brain imaging is Technetium 99 m-labeled Ethyl Cysteinate Dimer (ECD). ECD is a lipophilic compound with unique pharmacodynamics. It crosses the blood brain barrier and has high first pass extraction by the neurons proportional to regional brain perfusion at the time of injection. It reaches peak activity in the brain 1 min after injection and is then slowly cleared from the brain following a biexponential mode. This allows for a practical imaging window of 1 or 2 h after injection. In other words, it freezes a snapshot of brain perfusion at the time of injection that is kept and can be imaged later. This unique feature allows for designing functional brain imaging studies that do not require the patient to be inside the scanner at the time of brain activation. Functional brain imaging during severe burn wound care is an example that has been extensively studied using this technique. Not only does SPECT allow for imaging of brain activity under extreme pain conditions in clinical settings, but it also allows for imaging of brain activity modulation in response to analgesic maneuvers whether pharmacologic or non-traditional such as using virtual reality analgesia. Together with its utility in extreme situations, SPECTS is also helpful in investigating brain activation under typical pain conditions such as experimental controlled pain and chronic pain syndromes.

The Legacy of the TTASAAN Report – Premature Conclusions and Forgotten Promises About SPECT Neuroimaging: A Review of Policy and Practice Part II

“…we can see perfusion SPECT neuroimaging can serve as an objective biomarker of response to treatment ( 144 , 145 ), comorbidity ( 30 , 33 , 82 , 84 , 133 ), inherently difficult symptoms to objectify, such as pain ( 147 ), and of diagnostic masqueraders as described herein and elsewhere ( 30 , 33 , 84 , 133 , 148 ).…”

Radiotracers in the Diagnosis of Pain: A Mini Review

“…Technetium 99m-labeled ethyl cysteinate dimer (Tc-99m ECD) is used in brain perfusion studies because it effectively crosses the blood-brain barrier, has a rapid distribution time, and a 1- to 2-hour postinjection tissue retention time that together provide valuable information about regional cerebral blood flow and brain tissue metabolism. 12 13 16 Tc-99m ECD has been studied for the assessment of pain-related conditions by evaluating cerebral blood flow and metabolism in brain areas associated with pain perception and processing. For example, Nakabeppu et al 17 noted decreased bilateral thalamic perfusion in chronic pain sufferers.…”

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“…Computed Tomography (SPECT) imaging. With the SPECT technique, the patient receives an injection during the painful burn wound cleaning/debridement procedure (Bermo et al, 2021). The tracers in the injection go to the parts of the brain that are metabolically active at the time of injection (e.g., during painful wound care).…”