[18F]-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography is useful for studying glucose metabolism related to brain function. Here, we present a protocol for an [18F]FDG tracer set-up and semiquantitative assessment of the region-of-interest analysis for targeted brain areas associated with clinical manifestations in patients with severe traumatic brain injury.
Patients with severe traumatic brain injury (sTBI) have difficulty knowing whether they are accurately expressing their thoughts and emotions because of disorders of consciousness, disrupted higher brain function, and verbal disturbances. As a consequence of an insufficient ability to communicate, objective evaluations are needed from family members, medical staff, and caregivers. One such evaluation is the assessment of functioning brain areas. Recently, multimodal brain imaging has been used to explore the function of damaged brain areas. [18F]-fluorodeoxyglucose positron emission tomography-computed tomography ([18F]FDG-PET/CT) is a successful tool for examining brain function. However, the assessment of brain glucose metabolism based on [18F]FDG-PET/CT is not standardized and depends on several varying parameters, as well as the patient's condition. Here, we describe a series of semiquantitative assessment protocols for a region-of-interest (ROI) image analysis using self-produced [18F]FDG tracers in patients with sTBI. The protocol focuses on screening the participants, preparing the [18F]FDG tracer in the hot lab, scheduling the acquisition of [18F]FDG-PET/CT brain images, and measuring glucose metabolism using the ROI analysis from a targeted brain area.
Patients with sTBI are presented with unforeseeable neurological difficulties over the course of rehabilitation that include motor deficits, sensory deficits, and psychiatric instability1. Although clinical assessment is generally performed verbally, patients with sTBI such as unresponsive wakefulness syndrome or minimally conscious state have particular difficulty in knowing whether they are accurately expressing their thoughts and emotions because of disorders of consciousness, disrupted higher brain function, and verbal disturbances2,3. Family members, medical staff, and caregivers are sometimes confounded by unforeseeable neurological changes or the lack of response that can result from insufficient communicatory ability4,5.
Recently, multimodal brain imaging has been used to explore regional brain function6,7,8,9. The brain is the main consumer of glucose-derived energy, with glucose metabolism providing approximately 95% of the adenosine triphosphate (ATP) required for the brain to function10. The uptake of [18F]-fluorodeoxyglucose (FDG) is a marker for the uptake of glucose by brain tissue. [18F]FDG-PET/CT can detect [18F]FDG uptake and is, therefore, a useful tool for examining brain function11. In general, [18F]FDG image analysis is divided into two categories: ROI analysis and voxel-based analysis (VBA)12. Previous reports show that ROI analysis is preferred for studying specific regions of traumatic injury. This is because VBA (such as statistical parametric mapping [SPM]) requires coregistration and normalization to a standard brain, which does not work well in cases of TBI due to brain tissue deformation such as brain atrophy, swelling, enlargement, and shrinking of ventricular space7,12. Although various algorithms and software have been developed for analyzing magnetic resonance imaging (MRI) data, metals used in neurosurgical and orthopedic surgery generate noise artefacts7,12,13. Recently, the use of photomultipliers with PET/CT devices has improved the spatial resolution of PET/CT-derived brain images14. The current protocol focuses on semi-quantitatively measuring glucose uptake via ROI analysis in [18F]FDG-PET/CT using self-produced [18F]FDG tracers in patients with sTBI.
This study was performed in compliance with the institutional review board (approval No. 07-01) and adhered to the tenets of the Declaration of Helsinki. Informed consent for medical record and brain image use was obtained from the patients’ legal representatives. The study was conducted after approval by the institutional ethics committee (2017-14). This protocol was made following the guidelines of the Japanese Society of Nuclear Medicine and European Association of Nuclear Medicine as a reference15,16.
1. Screening of the Participants
2. Preparation of the [18F]FDG Tracer in the Hot Lab
3. Time Course for the Acquisition of the [18F]FDG-PET/CT Brain Images
4. Analysis of the [18F]FDG-PET/CT Images
A 63-year-old man who had been run over by a car while cycling was brought to the emergency room via ambulance. The examination revealed a Glasgow Coma Scale score of 7 (eye opening = 1, best verbal response = 2, best motor response = 4), anisocoria (right: 2 mm, and left: 3 mm), and a negative corneal response17. A CT of the head showed subarachnoid and intracranial hemorrhage and a skull fracture of the left zygoma, temporal bones, and parietal bones. The patient had no medical history and was managed conservatively. After nine months, he was admitted to the Rehabilitation Center for Traumatic Apallics Chiba. Examination at admission revealed a Coma Recovery Scale (Revised) score of 6 (auditory function = 0 [none]; visual function scale = 1 [visual startle]; motor function scale = 3 [localization to noxious stimulation]; oromotor/verbal function scale = 1 [oral reflexive movement]; communication scale = 0 [none]; arousal scale = 1 [eye opening with stimulation]) and spontaneous eye opening, but no evidence of language comprehension or expression20. Additionally, we saw no spontaneous limb movement, except for that associated with a change of systemic muscle tonus. We observed positive blink responses to loud sounds near his ear. He was regarded as having unresponsive wakefulness syndrome (previously referred to as vegetative state) by multi-disciplinary conferences.
To investigate thalamic activity for the possibility of neurological recovery, [18F]FDG-PET/CT was performed 13 months after the accident. [18F]FDG tracer was injected at a 242.4-MBq level of radioactivity.
Figure 2A shows that the glucose metabolism in the left thalamus was lower than in the right thalamus (right thalamus: SUVmax = 9.44, SUVmean = 5.93; left thalamus: SUVmax = 6.79, SUVmean = 4.53). The laterality ratio for SUVmax (SUVmaxleft/ SUVmaxright) was 6.79/9.44 = 0.72. Based on a previous report24, this suggested that the patient might become psychiatrically unstable over the clinical course.
Additionally, an overall view of the whole-brain [18F]FDG-PET/CT images showed that the peak glucose metabolism was in the left basal ganglia. Further, an examination of the three-dimensional brain-surface image showed that the glucose metabolism in the right frontal and parietal areas was higher than in the corresponding regions of the left hemisphere (see Figure 2C). Based on these data, clinical manifestations such as a level of wakefulness, motor activity, language comprehension and expression, visual and auditory cognition, facial expression, and psychiatric state can be compared with SUV values for the targeted brain area.
Figure 1: Schematic diagram of the time schedule for patient procedures and synthesis of [18F]FDG tracer. [18F]FDG: Fluorine-18 fluoro-2-deoxyglucose. Please click here to view a larger version of this figure.
Figure 2: Representative [18F]FDG-PET/CT brain image. (A) This panel shows a measurement of the right thalamic glucose metabolism viewed using the three-dimensional image browser. (B) This panel shows representative color-mapped images after [18F]FDG-PET and CT fusion. The blood glucose level at the time of the scan (maximum 15 g/mL) is depicted as red with a 50% SUVmax threshold. (C) This panel shows representative three-dimensional brain-surface [18F]FDG-PET images. The reddish regions have a higher glucose metabolism than the greenish regions. The blood glucose level at the time of scan (maximum 8 g/mL) is shown in red. (C) Images were constructed using advanced visualization software. [18F]FDG: 18F-fluoro-deoxyglucose; PET/CT: positron emission tomography/computed tomography. Please click here to view a larger version of this figure.
This protocol provides the means to conduct a series of brain-glucose metabolic assessments with [18F]FDG-PET/CT using self-produced [18F]FDG tracer at a single institution.
The production of [18F]FDG tracer follows the procedure described in the FDG synthesizer operator manual; however, caution is necessary regarding three points. First, the bombardment time and energy (step 2.5) should be adjusted according to the number of patients. Second, attention should be paid to the tube for 4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane because it can easily become stopped up by the crystallization of 4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane. Third, the hook of syringes (step 2.5.2) should be handled carefully because it tends to break.
Clinical assessment must be handled with caution. The condition of patients with sTBI is typically unstable due to fluctuations in awareness and mood, especially during the chronic stage. Therefore, multidisciplinary regular conferences (e.g., every six months) are needed to verify the patient status. Otherwise, clinical signs can be overlooked by the examiners19,20,21,22. To prevent misdiagnosis, several scoring systems, such as the Coma Recovery Scale-Revised and the Wessex Head Injury Matrix, should be used20,22. However, it is likely that these clinical assessments cannot be performed on the same day as the [18F]FDG-PET/CT.
Another point of caution is that patients can sometimes make unforeseen movements during image acquisition, such as muscle tonus or sudden epileptic seizures. Because anesthetic sedation can influence brain glucose metabolism, this protocol does not include a method for sedation13. Therefore, the possibility that image acquisition might be interrupted or needs to be suspended is unavoidable and should be prepared for.
The automated SUVs for single voxels corresponding to extraocular muscles and the scalp may include outliers. Further, the automated VOI using the imaging software can become less anatomically accurate depending on the SUV threshold and spatial resolution of the CT. Additionally, if only a small amount of [18F]FDG tracer accumulates, we should distinguish the focal active area from the surrounding tissues on the browser. However, assessment via PET/CT alone is essential because most sTBI patients have neurosurgical and orthopedic surgical metal in their bodies, making MRI impossible.
Although preparing the equipment for [18F]FDG tracer production in advance is necessary, the delivery of the tracer makes it easy to use in clinical studies that lack facilities with a cyclotron25.This [18F]FDG PET/CT approach for patients with sTBI has the potential to identify injured brain areas and residual brain function, which can be used for determining therapeutic targets. In the future, this protocol should be modified for use with advanced PET/CT imaging.
The authors have nothing to disclose.
The authors wish to thank Dr. Uchino in Sousen hospital for all procedures. The authors also thank Adam Phillips from the Edanz Group (www.edanzediting.com/ac) for editing a draft of this manuscript.
20ml syringe | Terumo | SS-20ESZ | |
10ml syringe | Terumo | SS-10ESZ | |
1ml syringe | Terumo | SS-01T | |
Protective plug | Top | ML-KS | |
Three-way cock L type 180° | Terumo | TS-TL2K | |
Extension tube | Top | X1-50 | |
Indwelling needle 22G or 24G | Terumo | SR-OT2225C | |
Tegaderm transparent dressing | 3M | 1624W | |
Hepaflash 10U/ml 10ml | Terumo | PF-10HF10UA | |
Auto dispensing and injection system | Universal Giken Co., Ltd. | UG-01 | |
Fluid for auto dispensing and injection system | Universal Giken Co., Ltd. | UG-01-001 | |
Millex-GS Syringe Filter Unit | Millipore | SLGSV255F | |
Air needle | Terumo | XX-MFA2038 | |
Check valve | Hakko | 23310100 | |
Saline 500ml | HIKARI pharmaceutical Co., Ltd. | 18610155-3 | |
Yukiban 25x7mm | Nitto | 3252 | |
Elascot No.3 | Alcare | 44903221 | |
Presnet No.3 27x20mm | Alcare | 11674 | |
Steri Cotto a 4x4cm | Kawamoto | 023-720220-00 | |
StatstripXp3 | Nova Biomedical | 11-110 | |
Statstrip Glucose strips | Nova Biomedical | 11-106 | |
JMSsheet | JMS | JN-SW3X | |
Injection pad | Nichiban | No.30-N | |
Stepty | Nichiban | No.80 | |
Advantage Workstation | GE Healthcare | Volume Share 7. version 4.7 | |
Discovery MI PET/CT | GE Healthcare | ||
EV Insite | PSP | ||
GE TRACERlab MXFDG synthesizer reagent kit | ABX | K-105TM | |
TRACERlab MXFDG cassette | GE Healthcare | P5150ME | |
Extension tube | Universal Giken Co., Ltd | AT511-ST-001 | |
TSK sterilized injection needle 18×100 | Tochigiseiko | AT511-ST-004 | |
TSK sterilized injection needle 18×60 | Tochigiseiko | AT511-ST-002 | |
TSK sterilized injection needle 21×65 | Tochigiseiko | AT511-ST-003 | |
Seal sterile vial -N 5ml | Mita Rika Kogyo Co., Ltd. | SSVN5CBFA | |
k222 TLC plate | Universal Giken Co., Ltd. | AT511-01-005 | |
Anion-cation test paper | Toyo Roshi Kaisha | 7030010 | |
Endospecy ES-24S set | Seikagaku corporation | 20170 | |
Sterile evacuated vial | Gi phama | 10214 | |
5ml syringe | Terumo | SS-05SZ | |
Extension tube | Top | X-120 | |
Finefilter F | Forte grow medical Co.Ltd. | F162 | |
Millex FG | Merck | SLFG I25 LS | |
Vented Millex GS | Merck | SLGS V25 5F | |
Injection needle 18×38 | Terumo | NN-1838R | |
Injection needle 21×38 | Terumo | NN-2138R | |
Water-18O | Taiyo Nippon Sanso | F03-0027 | |
Distilled water | Otsuka phrmaceutical | ||
Hydrogen gas G1 | Hosi Iryou Sanki | ||
Helium gas G1 | Hosi Iryou Sanki | ||
Nitrogen G1 | Hosi Iryou Sanki | ||
TRACERlabMXFDG | GE Healthcare | ||
Sep-Pak Light Accell Plus QMA | WATERS | ||
Sep-Pak Plus tC18 | WATERS | ||
Sep-Pak Plus Alumina N | WATERS | ||
HPLC with 3.9 X 300 mm columns | WATERS | ||
US-2000 | Universal Giken CO. Ltd. | ||
Kryptofix222 | Merck | ||
EG Reader SV-12 | Seikagaku Corporation | ||
UG-01 | Universal Giken Co., Ltd. | ||
syngo.via | Siemens Healthineers | ||
Advantage Workstation Volume Share 7, version 4.7 | GE Healthcare | ||
Q clear | GE Healthcare | ||
CRC-15PET dose calibrator | CAPINTEC, INC. |