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

A Clinical Comparison of Technegas and
Xenon-133 in 50 Patients with Suspected
Pulmonary Embolus*
Paulj Sullivan, M.D., FRACP; William M. Burke, M.B., B.S., F.C.C.P;
William M. Burch, M. Sc., Ph.D.; and
Frederick E. Lomas, M.D., FRACP
A comparison of "Technegas" and xenon-133 was performed
in 50 patients presenting with a clinical diagnosis of
pulmonary embolus. All patients underwent studies with
xenon inhalation, Technegas inhalation, and macroaggregated
albumin perfusion. Technegas is a new ultrafine
ventilatory agent with a particle size of 50 to 200A produced
from technetium pertechnetate and graphite in an argon
environment. Although particulate in nature, Technegas is
transported and diffuses like a gaseous agent. Its production
results in a high specific activity yield with high efficiency.
There is no significant deposition in the central airways,
and good peripheral visualization of the lung is obtained.
The study was designed to assess whether Technegas could
be used as a ventilatory agent to obtain high-quality
diagnostic images. All studies were reported as in normal
clinical practice, and no statistical analysis was performed.
The aim of the study was simply to see what role Technegas
had in a busy clinical department and how well it reflected
ventilation by comparison with xenon. Patient compliance
with Technegas was 100 percent and for xenon was 94
percent. Technegas enables one to obtain high-quality
ventilatory images and has an important role to play in the
assessment of pulmonary ventilation.
Ventilation imaging has greatly improved the diagnostic
specificity of lung scanning for pulmonary
embolism. 1-3 Agents currently used include krypton-
81m, xenon-133, xenon-127, and technetium-99m
radioaerosols, but all are less than ideal for different
reasons. Although krypton-81m produces high-quality
images,4'5 it is produced by cyclotron and is expensive
and limited in availability Xenon-133, more widely
used than krypton-81m, is limited because of its low
energy and high radiation dose and cost. Cost factors
also limit the use of xenon-127.
Taplin and Poe6 proposed a method of pulmonary
imaging with inhaled radioaerosols. Several agents
labelled with 99mTc including pertechnetate, sulfur
colloid, and pentetic acid (DTPA), as well as indium-
113m (JnCl3), have since been produced as aerosols.
The majority of these agents are rapidly cleared from
the lung after inhalation, and their relative low efficiency
(particle numbers per liter of carrier air) and
wide distribution of particle sizes (predominantly
>lI>) make them also suboptimum. Excessive deposition
in the central airways and poor peripheral
penetration occur in patients with chronic obstructive
pulmonary disease (COPD).
This report describes a new ventilation agent,
*From the Department of Nuclear Medicine, Royal Canberra
Hospital, and the Department of Medicine and Clinical Science,
J. C. S. M. R., Australian National University Canberra, Australia.
Manuscript received September 22; revision accepted January 7.
Reprint requests: Dr Sullivan, Department of Nuclear Medicine,
Woden Valley Hospital, PO Box 11, Woden ACT 2606, Australia
300
Technegas, in a clinical setting in a busy department.
It is a subjective appraisal of an agent as used in
everyday nuclear medicine. No attempt is made to
assess its region-by-region ventilation compared with
xenon, as the study was incorporated within normal
routines in a clinical department. Statistical analysis
was not performed. This report compares Technegas
as a ventilatory agent in routine clinical practice.
MATERIALS AND METHODS
Fifty adult patients (24 men and 26 women; age range, 28 to 85
years) with suspected pulmonary embolic disease were studied. All
were assessed clinically by history and examination, chest x-ray
film, blood gas analysis, forced expiratory volume in one second
(FEV,), and forced vital capacity (FVC). After giving written
informed consent, all patients underwent a standardized protocol
involving xenon inhalation, Technegas inhalation, and technetium
macroaggregated albumin perfusion studies. None of the patients
underwent angiography
The production of Technegas involves the evaporation to dryness
of 140 MBq (5 mCi) of sodium pertechnetate in physiologic saline
solution (standard generator eluent) in a graphite crucible. The
crucible is heated to 2,500°C in an atmosphere of pure argon for 15
seconds. The resulting vapor and argon mixture is inhaled by the
patient. A standard 12-mm bore polythene tubing connects the
Technegas generator to a mouthpiece unit. Oxygen can be added to
the gas stream if required. Inhalation is controlled by a handoperated
valve, and exhaled activity is trapped in an absorbent wad
via one-way valves at the mouthpiece.
Patients were supine for both inhalation and perfusion studies,
with the gamma camera (GE 400T) positioned for a posterior view
Following rehearsal for the Technegas procedure, patients then
inhaled and held their breath for up to five seconds and exhaled
back through the mouthpiece. The exhaled gases were diverted via
one-way valves to an efficient resin wood trap. Images were acquired
once the inspired count rate over the lungs reached 2,500 per
Comparison of Technegas and Xenon-133 (Sullivan et al)
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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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FIGURE 2. Posterior views with xenon-133 (top), Technegas (center),
and macroaggregated albumin (bottom) perfusion from 37-year-old
female diabetic whose study was within normal limits.
function, both radioactive gas and technetium aerosol
systems can be expected to perform well; however,
many patients seen in routine clinical practice suffer
from COPD, dyspnea, or are otherwise distressed or
enfeebled and unable to cooperate fully Three Xenon
studies in this series failed for such reasons. Using
aerosols, such patients show deposition in the central
airways with poor visualization of the peripheral areas
of the lungs.
With Technegas, compliance by patients is much
higher because there is little need for breath-holding
302
or rebreathing. Adequate lung images are obtained in
most patients with a single breath because of the high
production efficiency (up to 40 percent of initial eluent
as breathable activity in 4 L of argon). This high
efficiency also allows dynamic inhalation studies to be
performed.7
Alderson et al have compared xenon and radioaerosols
in 81 patients. These investigators9 found that
aerosols compared favorably with xenon-133 and concluded
that they were diagnostically equivalent. In
our study Technegas appeared diagnostically superior
to xenon-133. Whereas Alderson et a19 found more
ventilation in dependent pulmonary regions with
aerosols, we did not find this with Technegas, although
ventilation did parallel perfusion in its distribution in
normal lungs.
The distribution of particle size of Technegas is
proving technically difficult to determine but is in the
range of 50 to 200A, two orders of magnitude smaller
than typical aerosols and smaller than produced by
the new ultrasonic nebulizers. The half-life of Technegas
within the lungs follows the physical half-life of
Tc-99m, and there is no evidence of clearance across
the alveolar capillary membrane.
Nonclearance of Technegas allows high-quality multiple
planar and tomographic studies to be performed.7
When Technegas and perfusion tomography are performed
sequentially without moving the patient, identical
ventilation and perfusion slices can be analyzed
by computer for mismatching. This technique is impossible
with xenon.
There are three major reasons why Technegasproduced
ventilation images are more comparable to
the perfusion studies than other current ventilatory
agents, including xenon-133. First, similar pulmonary
depths are imaged, and resolution is the same, since
both studies use 9omTc. Secondly, some minor deposition
in the central airways was seen only in the sickest
patients, and often xenon-133 studies cannot be performed
in such patients. All xenon equilibrium images
contain activity in the conducting airways. Thirdly,
visualization of the peripheral lung is excellent. The
one exception in this series was caused by a technical
fault in the apparatus.
The other advantages of using
aOmTc for both ventilation and perfusion studies are
obvious, namely low cost, wide availability, ideal
energy, and half-life.
Provided that the following perfusion study uses
about five times the pulmonary activity of the ventilation
study, there is no significant degradation of the
perfusion image in analogue (film) recording. This is
readily calculated and obtainable with standard conventional
tracer doses. For computer-assisted studies,
it would be practical to use similar activities and
subtract the ventilation image.
Technegas is clinically a ventilatory agent of high
302Comparison of Technegas and Xenon -133 (Sullivan et al)
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FiCURE 3. Posterior projection with xenon- 133 (top left), Technegas
(upper right), and macroaggregated albumin (middle left) perfusion
and right posterior oblique projections with Technegas (lower right)
and macroaggregated albumin (bottom left) perfusion from 76-yearold
woman with acute onset of dyspnea, pleuritic chest pain, and
syncope. Right posterior oblique views assisted level of confidence
in diagnosis of pulmonary embolism.
quality It has distinct advantages over xenon-133. In
independent trials, the transport ofTechnegas through
the lungs is indistinct from gaseous agents, and therefore
although particulate in nature, Technegas may be
compared to gaseous agents. The capacity to obtain
multiple views directly comparable with the perfusion
study with excellent compliance and acceptance by
patients are the principal advantages. High-quality
diagnostic images can be routinely obtained with very
little effort in even very ill patients. The equipment is
compact and mobile.
The ability to perform dynamic and tomographic
studies of directly comparable ventilation and perfusion
images may well open an important new role for
computerized analysis.
Technegas allows high-quality ventilation imaging.
Its ease of use makes Technegas an ideal agent in busy
clinical nuclear medicine departments, and its method
of production may open up a whole new range of
technetium radiopharmaceuticals.
ACKNOWLEDGMENTS: To all the patients who so willingly
agreed to the formal requirements of the trial and made the work
possible; to the technicall, nursing, and clerical staff who cheerfully
took on the extra duties demanded by the trial protocol; and to
Arnersham (Australia) who provided the xenon-133 and disposable
breathing units, ouir sincere thanks.
CHEST 94 / 2 f AUGUST, 1988 303
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9 Alderson PO, Biello DR, Gottschalk A, Hoffer PB, Kroop SA,
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304
Comparison of Technegas and Xenon-i 33 (Sullivan et al)
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