Inclusion Criteria:

   1. Has the ability to understand and sign the written ICF and local medical privacy
   authorization forms, which must be obtained prior to the conduct of any study related
   procedures.

   2. Female subjects of non-childbearing potential must be either surgically sterile
   (hysterectomy, bilateral tubal ligation, salpingectomy, and/or bilateral oophorectomy
   at least 26 weeks before the Screening Visit) or postmenopausal, defined as
   spontaneous amenorrhea for at least 2 years, with follicle-stimulating hormone (FSH)
   in the postmenopausal range at screening, based on the local laboratory's defined
   ranges.

   3. Female subjects of childbearing potential (i.e., ovulating, premenopausal, and not
   surgically sterile) and all male subjects must agree to practice abstinence from
   sexual intercourse or use a medically accepted contraceptive regimen (including
   hormonal contraceptives) during their participation in the study and for 90 days
   (males) or 6 months (females) after Day 1. Medically accepted contraceptive methods
   are defined as those with 90% or greater efficacy and are as follows:

      1. Male subjects: condoms or surgical sterilization of subject at least 26 weeks
      before the Screening Visit (i.e., vasectomy).

      2. Female subjects:

         1. Surgical sterilization at least 26 weeks before the Screening Visit
         (includes hysterectomy or bilateral tubal ligation, bilateral oophorectomy,
         or salpingectomy);

         2. Intrauterine device or diaphragm with spermicide for at least 12 weeks
         before the Screening Visit; or

         3. Hormonal contraception (oral, implant, injection, ring, or patch) for at
         least 12 weeks before the Screening Visit.

   4. If male, subjects must agree to abstain from sperm donation through 90 days after the
   Day 1 Visit.

   5. Female subjects may not be pregnant, lactating, or breastfeeding.

   6. Female subjects of childbearing potential must have negative result for pregnancy test
   at Screening and Check-in.

   7. Subjects must have an estimated glomerular filtration rate (eGFR) of >45 mL/min/1.73m2
   at Screening.

   8. C-reactive protein level ≤10 mg/dL.

   9. Subjects must be willing and able to abide by all study requirements and restrictions.

   Inclusion Criteria Specific to ALS Subjects:

10. Adult (Age 18 to 80, inclusive) at the Screening Visit

11. Sporadic or familial ALS diagnosed as possible, laboratory-supported probable,
   probable, or definite as defined by the modified El Escorial criteria.

12. Forced vital capacity (FVC) of ≥50%; or if in the opinion of the investigator can lay
   flat for up to 90 minutes. If FVC has been performed within the past 6 months, this
   data may be used at the discretion of the investigator.

13. For ALS subjects, medication changes within 30 days prior to the Screening Visit
   should be discussed with the Medical Monitor.

   Inclusion Criteria Specific to AD Subjects

14. Adult (Age 40 to 80, inclusive) at the Screening Visit

15. Clinical diagnosis of early stage dementia, Alzheimer type, plus positive Aβ and tau
   PET imaging, cerebrospinal fluid (CSF) and/or plasma biomarkers consistent with 2018
   NIA-AA criteria

16. MMSE score >20 at Screening

17. AD medication changes within 30 days prior to the Screening Visit should be discussed
   with the Medical Monitor.

   Inclusion Criteria Specific to MS Subjects:

18. Adult (Age 18 to 70, inclusive) at the Screening Visit

19. MS medication changes within 30 days prior to the Screening Visit should be discussed
   with the Medical Monitor.

   Inclusion criteria specific to subjects with RRMS:

20. Diagnosis of RRMS based on 2017 McDonald criteria

21. If not newly diagnosed, subjects should have at least 1 documented relapse in the last
   24 months.

22. "Active disease" subjects should have at least 1 Gadolinium-enhancing (Gd+)
   T1-weighted brain or spinal cord lesion at Screening MRI.

23. "Disease in remission" subjects should have no Gd+ T1-weighted brain or spinal cord
   lesions at Screening MRI and stable clinical symptoms for at least 3 months prior to
   Day 1.

24. EDSS score between 2.0 and 5.5 inclusive at Screening

   Inclusion criteria specific to subjects with progressive MS:

25. Diagnosis of PPMS or SPMS based on 2017 McDonald criteria

26. EDSS score between 3.0 and 6.5 inclusive at Screening

27. No evidence of relapse in the prior 6 months

28. Neurological exam and symptom stability for ≥30 days prior to Day 1

29. Documented evidence of disability progression in the past 24 months not temporally
   related to a relapse

   Inclusion Criteria Specific to PD Subjects:

30. Adult (Age 55 to 80, inclusive) at the Screening Visit

31. Diagnosis of definite, idiopathic Parkinson's disease according to UK Parkinson's
   Society Brain Bank diagnostic criteria

32. PD medication changes within 30 days prior to the Screening Visit should be discussed
   with the Medical Monitor.

Overall Exclusion Criteria - For All Subjects:

Subjects meeting any of the following criteria will be excluded from this study:

   1. Body weight >120 kg

   2. Evidence of clinically significant or past medical history of hematologic, renal,
   endocrine, pulmonary, cardiac, gastrointestinal, hepatic, psychiatric, neurologic,
   immunologic, allergic disease (including multiple or clinically significant drug
   allergies) or any other condition that, in the opinion of the Investigator, might
   significantly interfere with the absorption, distribution, metabolism or excretion of
   study drug or place the subject at an unacceptable risk as a participant in this study

   3. History of recurrent kidney or liver malignancy

   4. Pacemaker or defibrillator or any non-removable metallic foreign objects in the body
   not compatible with MRI

   5. Inability to lie in a PET/CT or PET/MRI scanner for up to 90 minutes at a time

   6. Laboratory results (serum chemistry, hematology, coagulation and urinalysis) outside
   the normal range at Screening and Check-In and considered clinically significant in
   the opinion of the Investigator. Any elevation of aspartate transaminase (AST) and
   alanine transaminase (ALT) more than 3 times above the upper limit of normal at
   screening and/or check-in is exclusionary. One retest of an exclusionary laboratory
   result is allowed at the discretion of the Investigator and with approval from the
   Medical Monitor.

   7. Resolved acute illness considered clinically significant by the Investigator within 10
   days prior to Screening

   8. History of alcoholism or drug abuse within 2 years prior to Screening. No cannabinoid
   drug use for at least 10 days prior to Day 1.

   9. Positive urine drug test, marijuana test or cotinine test at Screening or Check-In

10. Any immunizations within the 28 days prior to screening

11. Received any other investigational medicinal product within 30 days or 5 half-lives
   (whichever is longer) prior to Day 1

12. Corticosteroid treatment (e.g., prednisone, solumedrol) within 30 days of Baseline

13. Treatment with any of the following classes of nonsteroidal anti-inflammatory drugs
   (NSAIDS): carboxylic acids, enolic acids, cyclooxygenase (COX) II inhibitors within 14
   days of Day 1

14. Lost or donated >450 mL of whole blood or blood products within 30 days prior to
   Screening

15. MRI exclusion criteria: findings that may interfere with interpretation of the PET
   imaging, including but not limited to significant cortical/subcortical cerebrovascular
   disease, infectious disease, space-occupying lesions, hydrocephalus or other
   abnormalities associated with CNS disease not related to ALS, AD, MS or PD

16. CT exclusion criteria include any medical device or metallic implant that may
   interfere with image acquisition or affect image reconstruction (e.g., CT attenuation
   correction).

17. Investigator has reason to believe that the subject may be unable to fulfill the
   protocol visit schedule or requirements

18. Has any finding that, in the view of the Investigator and Medical Monitor, would
   compromise the subject's safety in the trial

   Exclusion Criteria Specific to MS Subjects:

19. Clinical signs or laboratory findings suggestive of neuromyelitis optica (NMO)
   spectrum disorders or myelin oligodendrocyte glycoprotein (MOG)-associated
   encephalomyelitis (i.e., presence of anti-NMO [aquaporin-4] antibodies or anti-MOG
   antibodies)

20. Diagnosis of progressive multifocal leukoencephalopathy (PML)

   Exclusion Criteria Specific to PD Subjects:

21. Secondary, atypical, or genetic parkinsonism

   Exclusion Criteria Specific to HV Subjects:

22. Clinically relevant finding on physical examination at Screening

23. Family history of neurological disease that may confound interpretation of imaging
   results

24. History of any central nervous system disorder or brain trauma that could cause
   imaging abnormalities in the opinion of the Principal Investigator and Medical Monitor