 |
 Introduction
The new frontier in medical imaging technology is in
combined modality systems, or fusion imaging. On this leading edge
are the new hybrid imaging devices that combine CT scanner and
Positron Emission Tomography (PET) scanner functions. CT scanners
employ a well-established technology, using X-rays taken at
regularly spaced angles around the body to produce
computer-generated graphic projections and anatomic slices of the
region of interest. Because the imaging technique uses X-rays, the
imaging is sensitive to bone and hard structures but relatively
insensitive to soft structures. Diagnostic CT images provided
excellent patient geometry and scale but show only structure with
no information as to function.
PET scanners are a relatively new clinical technology, using the
decay properties of injected, high-energy nuclear medicine isotopes
to generate graphic projections of metabolic activity in a region
of interest. Because the imaging technique is based on the
detection of metabolic activity, it is very sensitive to living
tissue but completely insensitive to rigid structures. PET scanning
is becoming the method of choice in detection and classification of
cancerous tumors because of their uncharacteristic high metabolic
state. Diagnostic PET images provide excellent information about
cancerous tumor size and response to treatment but lack the
necessary patient landmarks to accurately locate the tumor for
precise surgical or radiation oncology treatments.
Major medical imaging vendors are now introducing hybrid devices
that combine the CT scanner functions and the PET scanner functions
into a common gantry. Parallel-processing image analysis and
volume-rendering computer systems have produced merged images that
superimpose PET metabolism on CT structures. These images provide
much more diagnostic information than either of the images viewed
independently.
Capability and Reality
As healthcare facilities begin to respond to the clinical pressure
to provide combined PET/CT capabilities, the first question will
always be, "How much is this thing?" The second question should be,
"What do we need to do to get our money's worth out of this
thing?"
The traditional single-slice-per-rotation CT scanner costs $400,000
to $800,000 and produces one image per one-second rotation of the
X-ray tube in the gantry. A traditional CT study would be scheduled
every 30 minutes and have a radiology staff member transport the
patients to and from an outpatient waiting room or their hospital
rooms. The waiting period is often 40 to 60 minutes. A typical day
would produce 16 patient studies of 60 to 80 images each. The
traditional CT scanner is rapidly being replaced by the multislice
CT scanner. The multislice scanner will fit in the same procedure
room with little modification except for the addition of a
dedicated chiller unit for the X-ray tube.
The multislice CT scanner is the new standard in healthcare and
will produce 4 to 16 imaging slices per rotation and operate at two
rotations per second, or 8 to 36 images per second, at a cost of
$1.2 million to $1.6 million. When a multislice scanner simply
replaces a single-slice scanner (see Scenario A), however,
facilities seldom see the expected increase in use. A multislice CT
study would require only 6 minutes per procedure, but patients are
still scheduled every 18 to 20 minutes because a radiology staff
member still transports the patients to and from an outpatient
waiting room or their hospital rooms. The waiting period is often
20 to 40 minutes. A typical day would produce 24 patient studies of
600 to 800 images each-only a 33 percent increase in total
procedures performed but a 330 percent increase in the number of
images to be interpreted.
 |
| Scenario A |
Although the multislice scanner can be much faster, it still
takes a fixed amount of time to move the patient into the room,
position the patient on the table, and move the patient out of the
room when the study is complete. Traditional departments that
assign one technologist to the CT scanner expect the turnover time
between patients to be 10 minutes-to allow for patient removal from
the scan room, changing the table covering, bringing the next
patient into the room, instructing the patient, and positioning the
patient on the scanner table. This turnover time has led facilities
with the much-faster multislice scanners to provide two or even
three staff members per scanner. While one staff member takes the
patient from the room, another can change the table covering and
set up the control console data for the next patient, while a third
is bringing the next patient to the scan room, instructing the
patient, and positioning the patient on the table. A staff of three
often can cut turnover time from 10 minutes to 3 minutes. With the
much shorter examination and turnover times, patient holding areas
often become the limiting factor in department efficiency. If the
patient is not yet in the department, or the last several patients
are still waiting to leave the department, patient unavailability
will negate any advances from faster machines and more staff.
By providing adequate area design and technical support, a
multislice CT scanner can schedule patients every 9 minutes for
general procedures. This requires a two- or three-place
prep/holding area that is staffed for patient transport (see
Scenario B). The holding area provides a staging area to maximize
the availability of the scanner and minimize the radiology
technicians' nonproductive time in moving patients. With proper
design and staffing, the same CT scanner can produce more than 54
patient studies per day-a 200 percent increase in total procedures
performed. Although the multislice CT costs twice as much as the
single-slice unit, it can triple the number of procedures performed
in one day, with adequate planning and design. The increase in
patient volume also reduces the need for additional CT scanners and
the associated construction, maintenance, and staffing costs.
 |
| Scenario B |
A fixed PET scanner currently costs $2 million and produces one
study every 30 minutes. Data acquisition times are long because
enough data must be captured to identify the source of the
metabolic activity. Occasionally, studies cover the patient's
entire body to detect possible metastasis of the primary tumor to
other secondary sites. An adequate whole-body scan can take up to
45 minutes. PET scans and CT scans have similar turnover times,
ranging from 3 minutes for a well-staffed department to 10 minutes
for a minimally staffed area. The PET scanner also requires a
nuclear isotope "hot lab" to prepare and calibrate the isotope to
be injected. Besides the technician to staff the hot lab, a nursing
staff member must start an IV in the patient to administer the
isotope. Therefore, in terms of scan efficiency, a prep/holding
area for the PET/CT patients is even more important than for
CT-only patients (see Scenario C).
 |
| Scenario C |
A combined PET/CT scanner currently costs $3 million and
generally produces one PET/CT study every 30 minutes or a simple CT
study every 9 minutes. The ability of the CT image to anatomically
locate the sources of the PET metabolic data allows a much shorter
acquisition time for diagnostic-quality images. The geometry of the
PET/CT allows both modalities to acquire data simultaneously and
ensure the accuracy of the image alignment. There have been
attempts to study patients by taking independent images with a CT
scanner and a PET scanner, then trying to index the images
together. This is a much longer and more expensive process, with
questionable results.
Impressive Equipment Speed Upgrades Are Not
Enough
Any benefits from the speed of the technical procedure may not be
realized without appropriate planning for the prep/holding areas
and staffing. The fixed time to move the patient and to prepare the
room for the next patient can be optimized. If it is not, however,
the entire throughput of the equipment is lost and the expected
revenue gains will not be realized. In turn, without the revenue
gains, there will additional pressure for more equipment, staff,
and space to meet growing demands in the department. These
interrelated factors can render the financial projections involved
in equipment justifications and department budgets null and
void.
Planning Methodology Changes
In the 1980s and 1990s, the planning methodology for radiographic
rooms was quite simple. When the patient examination and study time
was in the range of 30 to 60 minutes per procedure, turnaround time
and transport time were not critical factors. With this procedure
time range, a waiting room was considered adequate, and equipment
speed was always the limiting factor in department
production.
In the 2000s, the planning methodology must focus on keeping the
machine in use due to the tremendous increase in speed and the
decrease in procedure time. A comparison of Scenarios A and B shows
the increase in patient throughput and decrease in patient waiting
times that can be achieved through provision of holding areas and
transport personnel to support the speed of the multislice CT
scanner. The small additional cost of providing a double-stretcher
holding area and a nontechnical staff member increases machine use
by 100 percent.
The technology of a combined PET/CT scanner requires two holding
areas with different functions to enable more efficient patient
flow through the scanning area. The two holding areas are preferred
over a single combined area because the PET prep area has the hot
lab and requires that the IV line and isotope injection be
administered by a higher-level staff person than would be needed in
the routine holding area.
Another critical design factor is the physician's reading room. One
radiologist can read, interpret, and dictate the reports for daily
procedures on a single-slice CT scanner. A multislice CT scanner,
however, often requires two radiologists. The combined PET/CT
scanner requires the reading function of nuclear medicine and CT
with radiation oncology experience. Therefore, the reading room
demands will increase even though the equipment space requirements
may not.
Conclusion
Upgrades in medical technology affect the success of healthcare
planning and design even when the physical space requirements to
accommodate the equipment do not change. An understanding of the
changes in technology is critical to providing a design that will
best achieve the advantages promised in the glossy sales
presentations. Failure to properly support new technology with
functional design might both limit the productivity of the
installation and result in demand for additional equipment
purchases that should not be necessary.
|
