Compare Technegas Ventilation-Perfusion SPECT and Xenon Ventilation-Perfusion Planar Imaging for Pulmonary Embolism

Inclusion Criteria: Subjects will be enrolled in Cohort 1 if they meet the following requirements:

1. Male or female, at least 18 years of age.

2. Suspected of having PE and be a candidate for Xe-133 V/Q imaging.

3. Willing and able to provide informed consent.

4. Stable and able to undergo Xe-133 planar imaging, Technegas SPECT imaging, andplanar/SPECT perfusion imaging and complete follow-up procedures.

5. Willing and agree to complete study procedures, including follow-up safetyassessments.

6. Using adequate birth control, if female and fertile.

7. If female, has a negative urine or serum pregnancy test.

8. Agrees to return for a 24-hour and 30 day follow-up safety assessment. Subjects will be enrolled in Cohort 2 if they meet the above criteria AND subject is likelyto have pulmonary embolism based on one or more of the following:

9. Wells Score of 7 or greater. Subjects with a Wells Score less than 7 may be enrolledin Cohort 2 if there is agreement between the investigator and the medical monitorthat the subject is at high risk for PE.

10. An abnormal D-dimer test.

11. Positive Doppler ultrasound for DVT.

12. CTA is positive for PE within 24 hours of this imaging study.

Exclusion Criteria: Subject

1. Has undergone imaging with Iodine-131 (I-131) within 30 days, Thallium-201 (Tl-201) orIndium-111 (In-111) within 10 days, Fluorine 18 (F-18) within 24 hours, or any otherradiopharmaceutical not otherwise specified within 72 hours of this imaging study.

2. Has previously undergone an imaging study with a Tc-99m agent, within 48 hours of thisimaging study.

3. Is a pregnant or lactating female.

4. Has received Technegas in the past.

5. Was previously enrolled in another investigational study or received aninvestigational drug within 30 days prior to dosing.

6. Is hemodynamically unstable.

7. Has received therapeutic dose of low molecular weight or unfractionated heparin within 24 hours prior to dosing or Tissue Plasminogen Activator (tPA) within 4 hours prior todosing or has received treatment for PE between the time of a positive CTA, ifperformed, and Technegas V/Q SPECT imaging.