The project will be performed over a period of approximately two years. In the first year the [18F]FTHA tracer will be developed, optimized, and tested on normal volunteers. During the second year, the tracer will be investigated on patients with suspected obstruction of the thoracic duct (TD).

Initially up to 10 healthy adult volunteers will be recruited for the study. All subjects will be instructed to fast overnight before the scan visit. On the study day, subjects will be fasting, and then asked to consume an Ensure drink after [18F]FTHA administration and before imaging begins. Tracer administration vial oral capsules and PET/CT imaging: All subjects will receive approximately 1.0 -1.5 mCi (approximately 37-55 MBq) of [18F]FTHA administered orally followed by dynamic imaging for up to 4 hours, with breaks between scan sessions (Figure 4) on a whole-body PET/CT system.

An additional 15 patients with clinically suspected obstruction of the TD-venous junction with symptoms that may include chronic abdominal pain, edema, protein losing enteropathy and/or ascites, will be studied using the same administration and imaging procedures.

Participants with disease may undergo a standard of care clinical surgical bypass procedure and be asked to return post-surgery for a follow up PET/CT imaging session.

Inclusion Criteria:

Inclusion Criteria (Healthy Volunteer Cohort)

1. Male and female participants will be ≥ 18 years of age.
2. "Healthy Volunteer" is defined for the purposes of this study as a volunteer who is in good general health in the opinion of an investigator (some well controlled chronic medical conditions may be allowed at the discretion of an investigator if they do not believe they will interfere with the collection of imaging data, specific excluded medical conditions are listed under exclusion criteria).
3. Informed of the investigational nature of this study and able to provide written informed consent and participate in this study in accordance with institutional and federal guidelines prior to study-specific procedures.

Inclusion (Patient with suspected TD-venous junction obstruction cohort)

1. Male and female participants will be ≥ 18 years of age
2. Informed of the investigational nature of this study and able to provide written informed consent and participate in this study in accordance with institutional and federal guidelines prior to study-specific procedures.
3. Patient with chronic abdominal pain, ascites protein losing enteropathy, as well edema, with clinically suspected obstruction of the TD-venous junction and who are candidates for TD-venous junction plasty and or TD-Venous bypass

Exclusion Criteria:

Exclusion Criteria that apply to Healthy Volunteers only

1. Currently taking medication for cardiac disease, hypertension, hyperlipidemia, diabetes mellitus, heart failure, coronary artery disease, and/or history of cardiac surgery per medical record review and/or self-report
2. Known history of liver or kidney disease per medical record review and/or self-report

Exclusion Criteria that applies to Healthy Volunteers and Patients:

1. Women who are pregnant or breast feeding will not be eligible for this study; a urine pregnancy test will be performed in women of child-bearing potential on the day of each of the PET/CT scans.
2. Subjects who report claustrophobia or Inability to tolerate imaging procedures in the opinion of an investigator or treating physician
3. Self-reported difficulty with swallowing pills or allergy to components of Ensure Plus
4. Patients with a history of medical illness or disorder that in the opinion of an investigator and/or study physician could compromise patient safety or interfere with the collection of imaging data, or ability to complete the study and procedures, will be excluded.

Participant may not be involved in any other research studies involving ionizing radiation conducted within 1 year of their participation of this study.