This study will determine how breathing motions may affect positron emission tomography
(PET) scans. It has been discovered that the quality of PET scans varies according to which
part of the breathing cycle patients hold their breath.
NIH Clinical Center patients 12 years of age and older who are scheduled to have PET and
computed tomography (CT) scans as part of their standard medical care may be eligible for
Participants have their scheduled PET or CT scan as they normally would and are asked to
hold their breath after breathing out, as is usual. In addition, for this study, patients
are also asked hold their breath after breathing in and again at a point between breathing
in and out. Each breath-hold is for around 15 seconds. The scans for each of the three
different breath-holds are examined for differences.
Some patients may also be asked to breathe through a tube called a pneumotachometer, or
spirometer, to determine their normal breathing pattern. This involves breathing through a
mouthpiece similar to a snorkel mouthpiece and takes about 2 minutes.
Current clinical FDG imaging with the NIH's PET/CT machine (and in fact with most commercial
PET/CT machines) requires a CT scan be acquired prior to the PET scan. This CT scan is used
for attenuation correction of the PET data and to permit fusion of anatomical and metabolic
One difficulty with use of the CT scan for attenuation correction ('CTAC') is that the CT
scan is rapid compared to the breathing cycle. Each CT slice captures the lungs at one
(usually arbitrary) phase of the respiratory cycle. The PET data on the other hand take
many minutes to acquire, and so average the motion effects of the entire respiratory cycle
together. This 'freezing' of the respiratory cycle by the CT, and blurring of the
respiratory cycle during PET produces a mis-match between the PET and CT data. This
mis-match can produce improper attenuation correction during PET reconstruction, especially
at soft tissue/lung interfaces. The existence of this phenomenon has been reported in the
literature [1-7], especially at the dome of the liver, but it has not been thoroughly
quantified. Little or no data is available to indicate the quantitative errors the effect
produces in cardiac imaging. This despite the fact that the myocardium is only about
10mm thick, and it has been reported that the heart moves on average 9mm (and as much as
14mm) during a single average respiratory cycle.
The purpose of this protocol is to determine the degree to which respiratory motion may
influence quantitative PET imaging, especially at the lung/liver interface and free wall of
myocardium. By characterizing the magnitude of the effect, we hope to gain knowledge about
when correction for the effect is and is not necessary. It is hoped that the information
gained will also allow us to suggest potential methods to perform such corrections.
To gain the above information we will modify the CT acquisition protocol for subjects
already scheduled to undergo a whole body FDG PET/CT scan. In summary, rather than
acquiring the usual single full radiation exposure CT (taking approx 20-30 seconds), we will
acquire 3 CT scans (each taking approximately 20-30 seconds), each at 1/3 the usual
radiation exposure. Each CT will be acquired at a different phase of the respiratory cycle
(as opposed to current acquisition, which is only at end-expiration). The subsequent PET
data will be acquired as usual, but will be processed and analyzed separately with each of
the CT scans and also with a summed CT scan.
Note that subjects agreeing to participate in this protocol will receive no additional
radiation exposure. Participation in the protocol will extend the current overall scan time
(typically greater than 45 minutes) a very small amount (about 40-60 additional seconds for
imaging, and about 60 additional seconds for patient set up, etc).
- INCLUSION CRITERIA
Up to 30 subjects will take part in the study, chosen from sequential incoming clinical
patients who are scheduled for PET/CT studies of the torso and who have had or will have a
diagnostic CT within one week of the PET/CT study, without regard to disease. The number
of subjects selected for study per week will depend on patient load and availability of
scanner and technologist). Approximately an equal number of males and females will be
selected by alternating each selection between male and female. The selection of subjects
asked to participate will be random, in the sense that whenever technologist and analysis
time is available, the next subject scheduled for a whole body scan will be asked to
The only exclusion criteria will be subjects with respiratory difficulties.
Children under the age of 12.