Air Trapping and Emphysema Changes During Respiration in Chronic Obstructive Pulmonary Disease.

COPD is defined as a disease state characterized by the presence of airflow
obstruction and / or emphysema. Both are conventionally quantified using
pulmonary function tests (PFT). However, the ability of PFT to distinguish
airflow obstruction from emphysema is limited. Moreover, PFT is an integral
measure which generates no information about which part of the lungs is most
affected. With the use of CT it is possible to make a morphological
quantification of COPD. Emphysema can be measured directly, airflow obstruction
can be quantified by the amount of air trapping. CT therefore has the potential
to identify COPD subtypes and demonstrate which parts of the lungs are affected
by these subtypes. However, CT measurements vary during the respiratory cycle.
For that reason scans are made in suspended maximum inspiration or expiration,
but in practice inspirational levels are not totally constant even then. Little
is known about the exact changes in emphysema and air trapping on different
levels of inspiration. This can be studied using 4D CT. By performing
additional static scans the dynamic information can be transferred to static
setting (as in standard CT) and a suitable correction for variations in
inspiration can be developed.

1. To develop a method that lets us derive measures of air trapping and
emphysema from static CT that are independent of inspiration level.

In order to achieve this objective we need to:
2. study the influence of inspirational level on the extent of air trapping and
emphysema measurements using 4D CT data.
3. relate measurements of air trapping and emphysema score on dynamic (4D) CT
to static (3D) CT.

Patients participating in this study will receive a clinical 4D CT scan from
the radiology department. 4D CT is performed while the table is moving very
slowly, while the patient is breathing normally. Respiration is recorded and
synchronized with the CT data. Combined, a total chest CT for every specific
point in time during respiration can be reconstructed. This 4D CT will be used
for the planning of the radiation. We will use the 4D data to assess emphysema
and air trapping measurements on different inspirational levels. Next, 3 static
low dose CTs (inspiration, expiration, mid-respiration) are added to ensure
that the dynamic data can be reliable transferred to static CT.

The CT scans performed for the purpose of this study have a total dose of < 6
mGy. Participating will add 10 minutes to the clinical 4D CT scan time.