A Pilot Study to Correlate 4-18F- Fluoro-1-naphthol 18F-4FN PET/CT Imaging With Graft Versus Host Disease Manifestations

Eligibility Criteria 1. Acute or Chronic GVHD - acute and chronic GVHD criteria can be found at (Harris, Young et al. 2016)(Jagasia, et al. 2015). 2. Able to give written informed consent. 3. ≥18 years of age 4. Creatinine clearance ≥ 30 mL/min/1.73m2 5. Subjects may be planned to receive a new systemic therapy for GVHD 6. Prior / continuing systemic therapy for acute or chronic GVHD is allowed 7. KPS ≥ 20 8. Ability to understand and the willingness to sign a written informed consent document. 9. The effects of the study agent on the developing human fetus are unknown. For this reason, women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation. (Refer to Pregnancy Assessment Policy MD Anderson Institutional Policy # CLN1114). This includes all female patients, between the onset of menses (as early as 8 years of age) and 55 years unless the patient presents with an applicable exclusionary factor which may be one of the following: * Postmenopausal (no menses in greater than or equal to 12 consecutive months). * History of hysterectomy or bilateral salpingo-oophorectomy. * Ovarian failure (Follicle Stimulating Hormone and Estradiol in menopausal range, who have received Whole Pelvic Radiation Therapy). * History of bilateral tubal ligation or another surgical sterilization procedure. * Approved methods of birth control are as follows: Hormonal contraception (i.e. birth control pills, injection, implant, transdermal patch, vaginal ring), Intrauterine device (IUD), Tubal Ligation or hysterectomy, Subject/Partner post vasectomy, Implantable or injectable contraceptives, and condoms plus spermicide. Not engaging in sexual activity for the total duration of the trial and the drug washout period is an acceptable practice; however periodic abstinence, the rhythm method, and the withdrawal method are not acceptable methods of birth control. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately. 10. Men treated or enrolled on this protocol must also agree to use adequate contraception prior to the study, for the duration of study participation, and 4 months after completion of study agent administration. Exclusion Criteria 1. Unable to comply with all study procedures (for example, participants who are unable to come to all follow up visits because they live far away from the transplant center) 2. Pregnant or lactating women: pregnant women are excluded from this study because the effects of \[18F\]4FN in pregnancy are not known. 3. Subjects with contraindications to the use of \[18F\]4FN including confirmed allergy. 4. Participants with a body weight of 400 pounds or more, or a body habitus which precludes their entry into the bore of the PET/CT scanner, because the hardware is not intended to support that weight. 5. Any additional medical condition, serious concurrent illness, or other extenuating circumstance that, in the opinion of the investigator, may significantly interfere with study compliance. 6. Children below the age of 18 are excluded because of the unknown but potential risks of administration of radiopharmaceuticals to minors.