A Clinical Comparison of Technegas and Xenon-133 in 50 Patients ...

second (equivalent to about 37 MBq [1 mCi] in the lung). Adequate
counts were normally obtained in one or two inhalations. Sicker
patients often required several more breaths. Six planar views (100k)
were performed: posterior; posterior obliques; anterior; and anterior
obliques.
Xenon imaging in the posterior view was performed immediately
prior to the Technegas study A single-use disposable breathing
system (Atomic Products) was used. After inhalations of approximately
400 MBq of xenon-133 (11 mCi), a standard protocol of
breath-holding, equilibration, and washout was performed. Perfusion
imaging (macroaggregated albumin) was performed immediately
after the Technegas study An administered activity of 180
MBq (5 mCi) to maintain a pixel count ratio of about five times the
Technegas activity was used. Multiple planar images identical with
the Technegas sequence were collected.
Technegas and xenon images were compared for technical quality
and diagnostic value. The images were viewed and graded without
digital processing by two experienced nuclear medicine physicians
reviewing all studies in three sessions in isolation from other data.
Image quality was assessed on a scale of zero to five in terms of
interpretability All studies were reported as high or low probability
of pulmonary embolus or indeterminate; however, for this report,
only those diagnosed as a high probability of pulmonary embolus
were included as truly positive studies.
RESULTS
Thirty-nine patients had a risk factor of prolonged
bed rest or recent surgery Eleven had a past history
of phlebitis or previous pulmonary embolus. Thirtyseven
patients presented with dyspnea, and 32 had
pleuritic chest pain. There were 13 smokers and 12
ex-smokers. Electrocardiograms were normal in 27
patients and showed sinus tachycardia in 19. The chest
x-ray film was normal in 14 patients and showed
pleural effusions in 15 and atelectasis in six. Blood gas
analysis showed an oxygen pressure of less than 80
mm Hg in 37 patients, and 19 had an FEV1 of less
than 1.20 L.
Ten patients were diagnosed as having a high
probability of pulmonary embolism by the criterion of
the PIOPED trial.8 Diffuse matching defects thought
to be consistent with COPD were visible in 13 patients.
Diagnostic images with Technegas were obtained in
49 patients. One patient showed marked central airway
deposition with poor visualization of the peripheral
areas of the lungs. This was due to technical problems
with the prototype equipment.
Three patients were unable to cooperate sufficiently
to obtain a xenon study (Fig 1), and diagnostic images
were obtained in 46 patients. One image was uninterpretable
because of poor compliance by the patient.
In a subjective comparison of the quality of the
images, 37 studies were similar (Fig 2), ten had better
images with Technegas, and three had better images
with xenon. Diagnostically, Technegas was thought to
be better in 21 studies, with this predominantly due
to the multiple images obtained.
Of the ten patients diagnosed with pulmonary
embolism, the extra views with Technegas enabled a
more confident diagnosis in six (eg, Fig 3). Two of the
ten patients with pulmonary embolism were diagnosed
on the Technegas image but not with xenon. In both
patients the scan's diagnosis was based on the summation
of small subsegmental nonmatched defects.8
The subsequent course of both patients validated the
Technegas findings.
Patient compliance with Technegas was 100 percent
and was 94 percent with xenon. All patients who had
previously undergone xenon or aerosol studies reported
that a Technegas study was less demanding.
From a technical point of view, the Technegas study
was easier to perform and caused less disruption to
the patient's scheduling and camera time.
DiscusSION
The important role of ventilation lung scanning in
pulmonary embolism is well documented, and in
cooperative patients with relatively normal respiratory
FicuRE 1. Anterior Technegas (left) and perfusion (right) views of 84-year-old man with carcinoma of
prostate and pulmonary embolus. Patient was unable to tolerate xenon study
CHEST / 94 / 2 / AUGUST 1988 301
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