Patients:
Institutional review board approval and written informed consent were obtained.
The study was performed in twenty patients with COPD (mean age: 72 years,
range: 56-87 years) and ten healthy volunteers (mean age: 30 years,
range: 25-38 years) .
Patients information are summarized in Table 1.
Xenon-CT Protcol:
35% concentration xenon gas was produced by using a xenon control system (AZ-725 Xetron ; Anzai Medical,
Tokyo,
Japan) .
Xenon ventilation CT data were obtained after single vital-capacity inspiration of 35% xenon gas,
using dual-source and dual-energy technique after conventional chest CT.
Examinations were performed on a dual-source CT scanner (Somatom Definition FLASH,
Siemens Healthcare,
Forchheim,
Germany).
Scan and reconstruction parameters were as follows: tube voltage of 80 kV and 140 kV with respective tube currents of 280 and 119 mA,
a rotation time of 0.28 second,
collimation of 64 x 0.6mm,
pitch of 0.9,
reconstructed section thickness of 2.0 mm,
reconstruction interval of 2.0 mm,
and medium sharp reconstruction kernel,
D30f (Table 2).
Xenon Ventilation:
Many of xenon ventilation CT reported adopt long-time (about three minutes) ventilation or multiple breath method.
These methods have the advantage of obtaining stable data from many patients with different pulmonary conditions,
but they have some problems in evaluating pulmonary ventilation.
Most important and critical problem is that this method cannot avoid the influence of pulmonary blood flow,
because xenon reached and staying in alveoli diffuses to the pulmonary micro blood circulation according to the Fick’s law.
And because xenon has the anesthetic effect, blood oxygen pressure monitoring during and after examination is necessary to obtain patients’ safety.
In addition to these reasons,
in evaluating COPD lung,
we think multiple xenon gas inhalations may obscure air way disease and emphysema because of xenon circulation with intrapulmonary air way collaterals.
To resolve these problems above,
we adopt single inhalation method in this study.
However,
in our method,
there arises new limitation,
i.e.
because of the single inhalation,
the timing of xenon gas control (out flow) and start of CT scan is difficult without flow meter.
Thus it is necessary to undergo this examinaton with experienced doctors and technicians,
as well as making good consensus with patients about this procedure.
Data analysis:
Xenon enhanced image datasets obtained by dual-source CT with dual energy scan and conventional chest CT image datasets were sent to off-lined computer (MMWP,
Siemens Healthcare). Mean xenon enhancement values (XeV) of whole lung were measured by using three-material-decomposition method,
and %LAA scores are calculated.
Mean xenon enhancement valeus and %LAA scores are correlated with pulmonary function test results.
In addition,
three-dimensional images of both xenon enhanced images and non-enhanced images (LAA images) were reconstructed with volume rendering (VR),
and compared each other.