Economic report
Cost effectiveness of direct digital
radiography versus computed
radiography for chest examinations
CEP 07011
August 2007
Contents
2
Introduction ............................................................................................ 4
Method..................................................................................................... 7
Results .................................................................................................. 10
Conclusions.......................................................................................... 22
Acknowledgements.............................................................................. 23
References ............................................................................................ 24
Appendix 1: Cost estimates ............................................................... 26
Appendix 2: Processes for CR and DDR........................................... 29
Author and report information ............................................................ 32
CEP 07011: 2007
Summary
3
Chest imaging is undertaken for a wide range of clinical conditions and is one of the most
frequently performed X-ray examinations undertaken in the UK. Many X-ray departments
have a room dedicated to chest radiography. An efficient and high quality service for chest
imaging is important in meeting the requirements of the NHS 18-week patient pathway.
Currently, computed radiography (CR) and direct digital radiography (DDR) are the two
digital modalities available for undertaking this type of examination and have substantially
replaced film screen imaging. This project examined the relative cost effectiveness of CR
versus DDR for walk-in chest examinations with a single projection view per patient. A range
of throughputs (number of patients per day) was considered.
The average examination time for a chest examination was shorter using DDR than CR. It
was found that under ideal conditions the maximum throughput with 80% room utilisation is
95 and 185 patients per day for CR and DDR respectively.
In terms of costing the service, it was shown that if the throughput is less than 80 patients per
day, then CR may be the most cost effective imaging method. Between 80 and 95 patients
per day, the difference between the two modalities is negligible and will depend on each
individual service. For greater than approximately 95 patients per day with CR, extra
resources will be required: either extended working hours or using two operators. Therefore
above this level a DDR room is more cost effective.
DDR was shown to have a number of advantages over CR such as reduced queue sizes,
more efficient use of operator time and reduced patient waiting time. Additionally, for DDR,
the amount of time a patient spends in the X-ray department was found to be less, with fewer
patients having to wait for 30 minutes or more. Thus the service may operate more
efficiently with DDR and it may therefore be possible to use the equipment for additional
examinations such as shoulders and extremities.
CEP 07011: 2007
Introduction
4
Chest imaging is one of the most frequently performed X-ray examinations in the UK [1] and
X-ray departments often have a dedicated chest room. Over the last five years, imaging in
X-ray departments has changed predominantly from using film / screen to digital imaging.
Computed radiography (CR) and direct digital radiography (DDR) are the two digital
modalities available for undertaking this type of examination.
Digital imaging has been shown to be more cost effective than film/screen [2,3]. The aim of
this project was to examine the cost effectiveness for these two different modalities for walkin chest examinations. The whole process is costed for each modality from purchase of the
system to its disposal. For this project, a walk-in chest service was modelled where one
projection per patient is undertaken.
Patient Group
This project considers patients termed as ‘walk-in’ adults, who attend for the examination
without a hospital appointment. These can be sub-divided into two groups:
•
GP referrals: This patient group may be in the hospital for only this examination.
These patients are entitled to expect a short hospital visit. For an examination that
takes a few minutes, the overall hospital visit should be less than one hour, preferably
much less. This allows patients to schedule the examination around their own work
and/or family obligations.
•
Outpatient clinic referrals: These patients may have several different
examinations/tests undertaken in the one day. Again, the expectation of the patient
should be that the time spent in the X-ray department will be short in order to
complete all their examinations in a reasonable timescale. Referrals from an
outpatient department should be able to have the examination on the day of their
initial visit.
Related Policy and Guidance
Radiology departments generally have a target for keeping the time between request and
report to within 4 to 6 weeks, perhaps as short as 3 to 4 weeks. This is required to meet the
requirements for the NHS 18-week patient pathway [4]. The ability to offer a walk-in service
is advantageous to meet this target; a GP referred patient can attend a radiology department
within days of the GP appointment.
Technology
Computed radiography (CR) from a user point of view is very similar to traditional film/screen
radiography and can use existing X-ray equipment. The technology is cassette based and
so the cassette will have to be carried by the user between the vertical stand and the CR
reader.
CEP 07011: 2007
Introduction
5
There is a wide range of technologies, which could be described as direct digital radiography
(DDR). However, a common feature is that the imaging detector is an integrated part of the
X-ray system and the image is read out automatically without requiring user action. The
image will be available to the user to view within seconds of the exposure.
Advantages and disadvantages of modalities
The two modalities have a number of advantages and disadvantages in terms of image
quality, costs and patient throughput.
•
The patient throughput of a DDR system is known to be higher than a CR system [2,
5] as DDR images are available immediately after exposure whereas CR cassettes
have to be transported to a reader.
•
The cost of a CR system is less than that for a DDR unit, with an additional benefit
that the X-ray system does not need to be replaced for use with CR. Retrofit
detectors are available for DDR but usually the whole system is replaced.
•
DDR images may have better image quality than CR for chest imaging [6].
•
The DDR system is generally integrated into the hospital information system (HIS)
and therefore the name of the patient and associated examination will appear
automatically for the operator. The image will be automatically linked to that patient.
With a CR system the cassette or image must be manually linked to the patient’s
details on the HIS. Any mistakes in this process can be time consuming to correct.
Ergonomics
A modern, well-designed X-ray system should present few ergonomic problems. With CR
there may be some issues with the handling of the CR cassettes. The weight of the
cassettes can be a particularly important consideration if several cassettes have to be carried
at one time. When using a dedicated chest system, there is minimal patient handling for
adult walk-in patients. If the room is used for other examinations, then the X-ray equipment
will need to be re-positioned, the movements may be manual or powered depending on the
system.
Clinical benefits and disadvantages
The introduction of digital imaging to radiology has had many benefits.
•
Fewer images lost from patient files
•
More efficient storage of and access to images
CEP 07011: 2007
Introduction
•
Reporting process has improved [7]
•
Reduction of unreported and unavailable images [8]
•
Fewer retakes [8,9]
6
However, to date there is little evidence that the current technology has improved the overall
clinical outcome compared to film/screen imaging.
CEP 07011: 2007
Method
7
In order to measure the cost effectiveness, the whole lifetime cost for both CR and DDR for a
walk-in chest imaging service should be considered. This includes the costs for staff, capital
expenditure and running costs. The costs of the imaging process will depend on the number
of steps in the examination and the time taken for each step.
Measurement of time
A stopwatch with a lap timer was used to measure the times for each step in the chest
imaging process using CR and DDR. The times of particular interest were
•
Time from patient being called to entering X-ray room (site dependent).
•
Time from the patient entering the X-ray room to the operator calling the next patient.
•
Time for operator to check images are received by PACS.
•
Time for operator to walk from X-ray room to CR reader.
A database of times was produced for both modalities, these were used in the model rather
than simply using the average time for examinations. It is important to include the natural
variability of arrival times and examination times in an X-ray department. Any differences
between CR and DDR for the patient entering the X-ray room from the waiting room will be
due to local differences rather than the modality. Therefore the results for both modalities
were combined.
Attendance time
Patients do not arrive at regularly spaced intervals; there will be busy times and quiet times.
This can depend on many factors for the particular community, such as bus schedules and
clinic times. The distribution of patient arrival times was measured from information gained
from a PACS system over a period of 3 months.
Utilisation rates
The total time for each examination was calculated. The full time utilisation rate is calculated
from dividing eight hours (9 am to 5 pm) by the total examination time. It is impossible to
reach 100% utilisation of a room due to uneven arrival of patients and/or other interruptions
to the work. A more realistic figure is 80% room utilisation and this is commonly used in the
costing of X-ray rooms.
Modelling throughput
A computer model was developed to predict the waiting times of patients and number of
patients and companions in the waiting area. The model was produced using an in-house
programme written in IDL 6.2 (RSI, Boulder, Co).
CEP 07011: 2007
Method
The first stage of the model was to randomly allocate patients to one-hour time slots
according to the probability of each time slot. The probabilities are created from the spread
of attendance times. For each patient, a time between being called and entering the X-ray
room and a time from entering the X-ray room to leaving the X-ray room, was allocated
randomly from the database of times.
The model would then run through a day predicting the size of the queue, the operator time,
and the average wait time for each patient. This process was repeated 100 times to obtain
an accurate representation of the model.
The basic model and processes assumed the following:
General:
•
80% room utilisation
•
need to repeat 4.4% of the images [9]
•
hours of operation 9am to 5pm (continuous cover)
•
when no patients waiting the operator will check that images have been received by
PACS
•
no other interruptions e.g. PACS problems
•
ambulant patients
•
one operator working in the room.
Additionally for CR:
•
the mean time from inserting a 35 x 43 cm CR cassette into the reader to the image
being available for viewing is 45s [10].
The model was run again to give different conditions:
•
the effect of patient throughput
•
to have the CR reader either in a central area or in the X-ray room
•
increased examination time.
CEP 07011: 2007
8
Method
9
The model of workflow of a department with CR and DDR is shown in appendix 2.
Costs
The various costs for purchasing, running and disposing of a chest imaging system were
identified. The estimations were found from a number of sources: manufacturers, suppliers,
X-ray departments, NHS Estates departments and professional assumptions. The details for
this are found in Appendix 1.
CEP 07011: 2007
Results
10
Time measurement
The average time for a chest examination will depend on a number of factors such as
departmental procedure, operator skills, patient population and room design. Patients who
are infirm or have a poor understanding of English may take longer to examine.
The average times for undertaking chest radiography were measured for CR and DDR (table
1).
Table 1: Time and maximum throughput for CR and DDR
Average time between patient being called and
entering the X-ray room (s)
Average time between patient entering X-ray room
and calling next patient (s)
Average time to check image been transferred
successfully to PACS (s)
Average time for operator per examination (s)
No. of patients per 8 hr day: 80% / 100% utilisation
CR
DDR
21
21
188
73
30
30
239
96 / 120
124
185 / 232
Patient arrival time
The distribution for patient arrival time measured (figure 1) gave a peak between 11 am and
12 pm. However, this can be very different depending on the hospital.
Figure 1: Distribution of arrival times in X-ray department
P ercentage of patients
20%
16%
12%
8%
4%
0%
before
9 am
9-10 am 10-11 am 11-12 pm 12-1 pm 1-2 pm
Patient arrival time
CEP 07011: 2007
2-3 pm
3-4 pm
4-5 pm
Results
11
Whole life costs
Tables 2a-c show the lifetime costs for CR and DDR, assuming a 7 year lifetime from
installation. It is useful to compare the systems with the same throughput. It can be seen
that most of the costs are the same for both systems. Year 1 is the most expensive for a
DDR system due to the higher purchase costs of the system. The annual costs for the DDR
are lower for years 2 to 7 for the same workload, mostly due to less space requirements
(rent). The whole lifetime costs for both systems are similar for the same workloads. For 95
patients a day, the estimated lifetime cost (7 years) is £1.6 million for both CR (equating to
80% utilisation) and for the same patient throughput for DDR (equating to 40% utilisation).
The whole life cost for 80% utilisation for DDR is £2.6 million.
CEP 07011: 2007
Results
12
Table 2: Example costs for CR and DDR
Table 2a: CR (95 patients / day; 80% room utilisation)
Year
Purchase
costs
Enabling
CR reader
X-ray unit*
CR image
plates
Removal
Air conditioning
Running
costs
Consumables
Service CR
Service X-ray
Rent
Image storage
Staff cost
Purchase
process
Operator
Radiologist
Clerical
Management
Medical
physics
Annual costs
Lifetime costs
1
2
3
4
5
6
7
£20,000
£40,000
£50,000
£5,000
£0
£0
£5,306
£0
£5,520
£0
£1,800
£0
£2,394
£5,000
£2,000
£32,400
£23,940
£2,442
£5,100
£2,040
£33,048
£24,179
£2,491
£5,202
£2,081
£33,709
£24,421
£2,541
£5,306
£2,122
£34,383
£24,665
£2,591
£5,412
£2,165
£35,071
£24,912
£2,643
£5,520
£2,208
£35,772
£25,161
£2,696
£5,631
£2,252
£36,488
£25,413
£31,313
£85,078
£10,958
£6,594
£31,939
£86,779
£11,177
£6,726
£32,578
£88,515
£11,401
£6,860
£33,229
£90,285
£11,629
£6,998
£33,894
£92,091
£11,861
£7,138
£34,572
£93,933
£12,098
£7,280
£35,263
£95,811
£12,340
£7,426
£633
£205
£209
£213
£218
£222
£226
£337,422 £203,636 £207,467 £216,678
£1,630,000
Cost/patient
£215,353
£9.44
£224,931
£225,347
£22,113
* The cost of the X-ray unit may be in a different year.
CEP 07011: 2007
Results
13
Table 2b: DDR (95 patients/day; 40% room utilisation)
Year
Purchase
costs
Enabling
Capital
Removal
Air conditioning
Running
costs
Consumables
Service
Rent
Image storage
Staff cost
Purchase
process
Operator
Radiologist
Clerical
Management
Medical
physics
Annual costs
Lifetime costs
1
2
3
4
5
6
7
£20,000
£200,000
£1,800
£4,000
£2,394
£10,000
£18,000
£23,940
£2,442
£10,200
£18,360
£24,179
£2,491
£10,404
£18,727
£24,421
£2,541
£10,612
£19,102
£24,665
£2,591
£10,824
£19,484
£24,912
£2,643
£11,041
£19,873
£25,161
£2,696
£11,262
£20,271
£25,413
£31,288
£85,078
£10,958
£6,594
£31,914
£86,779
£11,177
£6,726
£32,552
£88,515
£11,401
£6,860
£33,203
£90,285
£11,629
£6,998
£33,867
£92,091
£11,861
£7,138
£34,544
£93,933
£12,098
£7,280
£35,235
£95,811
£12,340
£7,426
£633
£205
£209
£213
£218
£222
£226
£434,998 £191,982 £195,580 £199,248
£1,640,000
Cost/patient
£202,986
£9.52
£206,797
£212,481
£22,113
CEP 07011: 2007
Results
14
Table 2c: DDR (185 patients/day; 80% room utilisation)
Year
Purchase
costs
Enabling
Capital
Removal
Air conditioning
Running
costs
Consumables
Service
Rent
Image storage
Staff cost
Purchase
process
Operator
Radiologist
Clerical
Management
Medical
physics
Annual costs
Lifetime costs
1
2
3
4
5
6
7
£20,000
£200,000
£1,800
£4,000
£4,662
£10,000
£28,200
£46,620
£4,755
£10,200
£28,764
£47,086
£4,850
£10,404
£29,339
£47,557
£4,947
£10,612
£29,926
£48,033
£5,046
£10,824
£30,525
£48,513
£5,147
£11,041
£31,135
£48,998
£5,250
£11,262
£31,758
£49,488
£31,288
£165,678
£21,339
£6,594
£31,914
£168,991
£21,766
£6,726
£32,552
£172,371
£22,201
£6,860
£33,203
£175,819
£22,645
£6,998
£33,867
£179,335
£23,098
£7,138
£34,544
£182,922
£23,560
£7,280
£35,235
£186,580
£24,031
£7,426
£633
£205
£209
£213
£218
£222
£226
£561,127 £320,407 £326,345 £332,396
£2.580,000
Cost/patient
£338,564
£7.66
£344,850
£353,057
£22,113
The number of patients being imaged per day was varied in the model to examine the effect
on both systems. Figure 2 shows that the cost per patient reduces with increasing patient
throughput, at a certain point the patient queue gets too large and the costs of the system
increase. At low patient throughput, CR is more cost effective. The model used showed a
cross over point of which DDR becomes more cost effective at about 95 patients per day.
However, there are a large number of assumptions and uncertainties in the measurements,
therefore a broad result is that for a patient throughput of less than 80 patients per day and
CR is more cost effective. The 80% utilisation was estimated to be 95 patients per day (one
operator, 9 am to 5 pm), it is not possible to increase this rate without either extending
working hours or using two members of staff. Both of these methods increase the costs and
would indicate that DDR is more cost effective above 95 patients per day. For patient
throughputs between these limits then the costs are very similar and will depend on local
conditions.
CEP 07011: 2007
Results
15
Figure 2: Cost effectiveness of CR and DDR with varying patient
throughput
Examination cost per patient
£16
DDR
£14
CR
£12
80% utility
£10
£8
£6
£4
£2
£0
0
50
100
150
200
Throughput (patients/day)
Cost effectiveness is not necessarily the only criterion. The quality of service is also
important, figures 3, 4 and 5 show the amount of time patients spend in an X-ray department
is less when using DDR and also there are far fewer cases of patients having to wait 30
minutes or more. Therefore the service to the patients can be improved when using DDR.
Average time (waiting + exam time)
(min)
Figure 3: Average time for patient in waiting and X-ray rooms
70
60
DDR
CR
50
80% utility
40
30
20
10
0
0
50
100
150
Throughput (patients per day)
CEP 07011: 2007
200
Results
16
Figure 4: Maximum queue size
35
DDR
CR
30
80% utility
Patients
25
20
15
10
5
0
20
50
80
110
140
170
200
Throughput (patients/day)
Figure 5: Number of patient waiting longer than 30 minutes
100
90
DDR
80
CR
Patients
70
80% utility
60
50
40
30
20
10
0
40
60
80
100
120
140
160
180
200
Throughput (patients/day)
The capital cost of the unit can have an influence on the cost effectiveness of the system.
The range of costs of a CR system is relatively small (typically £30,000 to £50,000) and has
little impact in the cost effectiveness. However, the cost of a DDR system has much wider
range depending on the technology, design and flexibility of the system (between £150,000
and £250,000). Figure 6 shows the effect on cost per patient. If the system costs £150,000
then the cost per patient over a period of 7 years is £7.50, but can be as much as £7.80 for a
system costing £250,000.
CEP 07011: 2007
Results
17
Figure 6: Effect of capital cost of DDR on cost per patient (80%
utilisation)
£7.90
Cost per patient
£7.85
£7.80
£7.75
£7.70
£7.65
£7.60
DDR
£7.55
£7.50
£150,000
£170,000
£190,000
£210,000
£230,000
£250,000
Cost of DDR
CR reader in X-ray room
The current model is based on the CR reader located in a central area, this increases the
walking time of the operator. A different model would be to have a single plate CR reader in
the X-ray room. In the measurements used for this report, the time from the X-ray room to
and from the CR reader is 20 seconds. When this time is removed from the model then the
whole life cost over 7 years drops by £20,000, which is negligible in this model. However,
the improvements are in the quality of service; the average wait for a patient drops by nearly
eight minutes and the number of patients waiting for more than 30 minutes drops from 35 to
18. The 80% room utilisation will also rise to 105 patients per day. Further benefits may be
gained if the reader is fully integrated into room. In this case the CR reader would
communicate with the hospital information system and the X-ray unit.
Patient impact and benefit
The computer model showed that DDR could improve the throughput of a room, which
should result in shorter queues. It also showed that a walk-in service is possible for both
modalities but would operate more successfully with DDR, though which would be the most
cost effective would depend on the throughput required. A walk-in service will allow patients
to be seen earlier than using an appointment service. Thus DDR is more effective at helping
hospitals meet the 18-week pathway.
Service impact
Any difference in image quality between the modalities, which may affect patient diagnosis,
was not costed. This can have a very large effect on the clinical outcome and also different
treatments needed or lack of early intervention with a possible knock on effects to other
CEP 07011: 2007
Results
18
departments. Currently, there is no evidence of any differences in patient diagnosis between
CR and DDR.
Patient choice is being introduced into the NHS. If a department has DDR, the waiting time
is potentially less, which may encourage patients to choose hospitals with DDR. This could
have a positive impact on the department’s finances.
Figure 7 shows the spare capacity available in each room for different patient throughputs. A
spare capacity with a negative value indicates that extended working days are required to
obtain that throughput. The CR room throughput can be improved by using two operators
(Appendix 2), but this is not considered in the model. The DDR room has the highest spare
capacity, therefore, to achieve the full financial benefit from the systems, it should be
possible to undertake other examinations in the room e.g. shoulders, extremities. However,
for other examinations, the system may need variable focus to detector distance and tiltable
detector. These may be more expensive than a dedicated chest unit.
Figure 7: Spare capacity in room
500
DDR
CR
Spare capacity (min)
400
80% utility
300
200
100
0
0
50
100
150
200
-100
Throughput (patients/day)
Reliability of equipment
No information could be found in the literature on the reliability of CR and DDR systems. In
the opinions of the authors of this report, modern X-ray tubes and generators used in general
radiography are considered to be very reliable. Both CR and DDR are considered reliable,
however if there is downtime on the DDR detector then the room will be out of action unless
there is a CR back-up in the department. For CR, most departments will have more than one
reader, therefore the room may continue working although there may be delays depending
on the location and spare capacity of the other readers.
CEP 07011: 2007
Results
19
Replacement of a DDR detector can be expensive. There are currently no statistics
available on the failure rate of detectors, but consideration should be given to including the
replacement of detectors in the service contract. If a DDR detector needs to be replaced
outside of the contract in, for example, year 4, at a cost of £50,000, the cost of per patient will
rise from £9.50 to £9.80 for a throughput of 95 patients per day.
Most experience has been with CR systems. The damage to image plates tends to be
mechanical and so the lifetime is more predictable. The CR cassettes will need to be
regularly replaced depending on the usage, this has been included as a regular replacement
every 10,000 images.
Economic benefit
This work has shown that the economic benefit depends on a number of factors, including
the number of patients per day. For this project, only the case of walk-in chest examinations
has been considered. This is likely to be the examination that shows the largest benefit in
terms of patient throughput. Other examinations where more time is spent in aligning and
positioning patients will result in lower throughputs and thus the economic balance between
CR and DDR will change.
The wider economic benefit of patient time has not been considered in this model. If a
patient spends less time having hospital examinations then they may have to take less time
off work, with reduced incidental costs (e.g. car parking, child care).
The CR system will have the lowest initial cost, particularly as the X-ray unit may not need
replacing at the same time. However, assuming a 7 year life cycle, the X-ray system will
need to be replaced at some point in time. In this report, it has been included in the first year
but could be replaced at any point in the life cycle.
Sustainability
The lifetime of the equipment is assumed to be 7 years. This is taken from a PASA
document [11] that suggests manufacturers should be able to supply parts and support for at
least 7 years, with a wish that equipment should last at least 10 years. For the 80%
utilisation figures then the cost per patient if 10 years is reached reduces from £9.40 to £9.30
for CR and from £7.70 to £7.50 for DDR. This does not take into account any changes in
downtime due to equipment ageing. The saving is quite small and this is indicative that the
purchase cost of the equipment is only a part of the whole life costs. It would be in the
interest of the environment and NHS finances for the equipment to last at least 10 years.
The Waste Electrical and Electronic Equipment Regulations 2006 [12] will have an impact on
the purchase and disposal cost of X-ray imaging equipment.
No studies could be found to compare the technologies in terms of waste disposal. It should
be noted that these systems are an improvement on film / screen imaging in that there is no
waste from processing chemicals and silver compounds.
CEP 07011: 2007
Results
20
Materials used in these systems are similar to those included in most electronic goods e.g.
PCs, digital cameras, photocopiers. The main source of environmental impact will come
from the manufacture, energy consumption, and disposal of the computer systems needed to
run the digital systems. This is likely to be very similar for each of the competing systems.
X-ray systems are very energy inefficient and require considerable power.
Extending the model to other examinations
The model presented in this report is for a walk-in chest service. It should be noted that this
is considered the fastest examination in an X-ray department. Other examinations will have
longer positioning time and extra views. For other examinations, or chest radiography of
patients in a wheelchair, the cost benefit equation will change between CR and DDR. In a
simple extension to the model, the examination time was increased to account for increased
positioning time, whilst keeping only one view.
Table 3: Variation in examination time
Extra time (s)
CR
DDR
Cost per patient for 80%
0
£9.40
£7.70
utilisation
30
£9.90
£8.20
60
£10.40
£8.40
90
£10.70
£9.20
0
95
185
30
85
150
60
75
125
90
70
110
80% utilisation
(No. of patients in 8 hr day)
The extra examination time changes the cost effectiveness and throughput of the systems.
The utilisation rate dropped for DDR more rapidly than for CR. Therefore, for longer
examination times, the difference in cost effectiveness between the modalities reduces.
Limitations of the study
The results from this report are broad and the actual costs will depend on a wide range of
factors including the procedures within the X-ray department. The model cannot simply be
extended to be applicable to all X-ray rooms in a department. The situation becomes more
complex when multiple views are taken. In some departments, it may be possible to reduce
the number of X-ray rooms used and this would have a large effect on the costings. The
reliability and speed of individual PACS systems will also have a large effect on the cost
benefit analysis.
The systems here are assumed to be typical systems. However, each system will have
advantages and disadvantages. The read cycle of the CR readers can vary between
CEP 07011: 2007
Results
21
manufacturers; line scanning readers in particular have a much shorter read cycle. Some
systems will be better than others in helping the workflow of the department.
This study cannot be simply extended to all chest examinations. If a significant proportion of
the patients are very infirm or wheelchair bound, then the room throughput will reduce due to
the increased time required for positioning the patient.
CEP 07011: 2007
Conclusions
22
In the financial climate of the NHS, value for money is considered very important. When
considering the procurement of new X-ray equipment, it is essential to ensure that purchase
is justified and that there are sufficient patients for the service. Ideally, the room should be
used for the maximum amount of time. However, it is inevitable that 100% utilisation is not
possible and that 80% is considered more realistic. Our models indicated that 80% is
realistic, otherwise there are large queues of patients and overtime may be required to cover
the backlog.
Our measurements and model are consistent with other work, in that a DDR room can
provide a higher throughput than a room using CR for a walk-in chest service [3, 5].
In terms of costing the service, it was shown that if the throughput is less than 80 patients per
day, then CR may be the most cost effective imaging method. Between 80 and 95 patients
per day, the difference is negligible and will depend on the individual service. To achieve
greater than around 95 patients per day for a CR room will require extra resources: either
extended working hours or using two operators, therefore above this level a DDR room
would be more cost effective.
If the patient throughput is high for a room using CR, or the central CR reader is not close to
the X-ray system, then it may be worth considering using a single cassette CR reader in the
X-ray room.
There are a number of advantages for DDR in terms of reduced queue sizes and more
efficient use of operator time and patient waiting time. The model presumes that there is no
difference in the total number of patients arriving for a chest X-ray. However, the DDR
system has higher spare capacity, therefore more patients would make it more cost effective.
The extra patients could come from a number of sources:
•
With patient choice more patients may be attracted to a service with lower waiting
times
•
Undertaking other examinations e.g. shoulders, extremities
This report is intended for service managers and superintendent radiographers, to help give
guidance on choices and costings of chest rooms. Further work would need to be
undertaken to examine other examinations or number of X-ray rooms, which might be most
cost-effective for the local patient workload.
CEP 07011: 2007
Acknowledgements
23
The staff of KCARE would like to acknowledge the assistance of GE Medical and Agfa
Healthcare.
The KCARE staff would also like to thank the staff of the radiology departments of St
George’s Hospital, Guy’s Hospital and King’s College Hospital for their assistance during the
evaluation.
CEP 07011: 2007
References
24
1
Hart D, Hillier MC, Wall BF, “Doses to patients from Medical X-ray Examinations in
the UK 2000 Review” NRPB report W14 (2002)
www.hpa.org.uk/radiation/publications/w_series_reports/2002/nrpb_w14.htm [last
accessed 9/7/07]
2
Andriole KP, "Productivity and Cost Assessment of Computed Radiography, Digital
Radiography, and Screen-Film for Outpatient Chest Examinations" J. Digit. Imaging
15, 161-169 (2002).
3
Andriole KP, Luth DM, Gould RG, “Workflow assessment of digital versus computed
radiography and screen-film in the outpatient environment” J. Digit. Imaging 15 sup 1
124-6 (2002)
4
NHS Delivering the 18-week pathway http://www.18weeks.nhs.uk [last accessed
24/5/07]
5
Reiner BI, Siegel EL, Hooper FJ, Siddiqui KM, Musk A, Walker L et al, "MultiInstitutional Analysis of Computed and Direct Radiography: Part I. Technologist
Productivity," Radiology 236, 413-419 (2005).
6
Ganten M, Radeleff B, Kampschulte A, Daniels MD, Kauffmann GW, Hansmann J,
“Comparing Image Quality of Flat-Panel Chest Radiography with Storage Phosphor
Radiography and Film-Screen Radiography” AJR; 181:171-176 (2003)
7
Bryan S, Weatherburn G, Watkins J, Roddie M, Keen J, Muris N et al “Radiology
report times: impact of picture archiving and communication systems” AJR 170: 11539 (1998)
8
Siegel EL, Reiner BI, “Filmless radiology at the Baltimore VA Medical Center: a 9
year retrospective” Computerized Medical Imaging and Graphics 27 101–109 (2003)
9
Weatherburn GC, Bryan S, West M, “A comparison of image reject rates when using
film, hard copy computed radiography and soft copy images on picture archiving and
communication systems (PACS) workstations” Br J Radiol 72 653-660 (1999)
10
Report 06033 “Computed Radiography (CR) systems for General Radiography. A
Comparative Report Edition 3” Centre for evidence based purchasing (CEP) (2006)
www.pasa.nhs.uk/pasa/Utilities/RenderDocument.aspx?Path=%5BSPSMachineNam
e%5D/sites/WWWDocuments/Shared%20Documents/About%20procurement%20in
%20the%20NHS/Centre%20for%20Evidence%20based%20Purchasing/Xray/Report_06033.pdf [Last accessed 24/5/07]
11
PASA “NHS supplementary conditions of contract for the supply, installation and
maintenance of clinical radiology and clinical oncology equipment” (Jan 2005
)www.pasa.nhs.uk/pasa/Doc.aspx?Path=[MN][SP]/Guidance%20Documents/terms%
CEP 07011: 2007
References
25
20and%20conditions/cracoe%20suppl%20january%202005%20without%20guidance
%20notes%20www.doc [last accessed 17/5/07]
12
The Waste Electrical and Electronic Equipment Regulations 2006, statutory
instruments 2006 No. 3289, Stationary office ltd
(www.opsi.gov.uk/si/si2006/20063289.htm) [last accessed 22/5/07]
13
Primary care NHS estates (www.primarycare.nhsestates.gov.uk) [last accessed
26/6/07]
14
Avrin D, Morin R, Piraino D, Rowberg A, Detorie N, Zuley M, et al, “Storage,
Transmission, and Retrieval of Digital Mammography, Including Recommendations
on Image Compression” JACR 3, 609-614 (2006)
CEP 07011: 2007
Appendix 1: Cost estimates
26
Whole life costs
An annual rate of inflation of 2% is assumed. The 18-week programme [4] identified that
there will be year on year growth for imaging examinations and so an annual increase of 1%
in the number of patients is included.
Capital cost
Purchase costs: The cost of an average DDR was based on information from UK suppliers
and ECRI. The purchase price was found to be between £150,000 and £250,000. Using a
retrofit system with an existing X-ray system can reduce the initial costs. However, in the
model used, the cost of a new X-ray system would be included later on in the life cycle. The
cost of a CR reader was assumed to be a single plate reader or half of a multi-plate reader
(shared between two rooms), taken from CEP report 06033 ‘Computed Radiography (CR)
systems for General Radiography. A Comparative Report Edition 3’ [10] and ECRI. For
chest imaging with CR, we assume the purchase of five 35 x 43 cm cassettes that are
replaced after 10,000 reading cycles. The cost of the X-ray system was taken from UK
suppliers and ECRI.
Enabling and removal costs: The removal costs are generally included in the purchase costs
of a new system, but have been included separately in this report. This information was
gained from suppliers. The assumption is that the X-ray room already exists and will be
replaced by a new X-ray system at the end of its life. Therefore, there are no costs of
installing radiation shielding, electrical supply and other services.
Service: The service costs were obtained from suppliers and hospital records. The service
contract of the DDR system includes replacement of detectors. If this is not included then
the service is cheaper, but if a detector needs to be replaced this can be expensive.
Air conditioning: While many new build hospitals have air conditioning as standard, this is
not the case for many existing hospitals. A number of DDR systems recommend having air
conditioning to provide optimal operation and lifetime of the detector. The costings were
based on discussion with hospital departments.
Staff costs
In the NHS there is a unified pay scale, decided under Agenda for Change. This makes it
simple to estimate the hourly cost. The annual salary was estimated as the average for the
appropriate band. The calculation then accounts for 8 weeks annual leave and public
holidays and 2 weeks sick leave plus 20% for employers contribution to national insurance
and pensions.
The operator was estimated to be on a band 5 pay scale. The model assumes continuous
cover of a room. Any work after 5pm is charged at a rate of time and a half.
CEP 07011: 2007
Appendix 1: Cost estimates
27
The clerical staff who deal with the paperwork, reception and telephone calls were calculated
as a band 4. This was assumed to be two minutes in total per patient. It is assumed that the
radiologist is using voice recognition software for the reports.
The medical physics staff who perform acceptance testing and routine quality assurance
were estimated to be assimilated to band 7 and the radiation protection adviser as a band
8C. This service would likely be part of a wider package for other rooms.
The radiologist cost was assumed to be a total of £130,000 per annum. The time to report
on an image was assumed to be 155s [7]. This was assumed to be the same for both CR
and DDR.
The management costs are assumed to be 10% of a manager at grade 8B.
Purchase process: The purchase process has an associated cost. There is a wide range of
staff potentially involved: service managers, operators, radiologists, medical physics,
purchasing officers, and estates. The work will include writing a specification, site visits,
purchasing meetings and meetings with suppliers. It was assumed that this takes 100 mandays and the average staff member is paid as a band 8A.
Running costs
There is a room running cost to account for lighting, heating, cleaning, and periodic
refurbishment for both the X-ray and waiting room. This generally has a cost per area. It is
assumed that the X-ray room floor space is 16 m2; this is estimated to be the smallest area
practical for a chest imaging room. The waiting room is a minimum of 5 m2 (4 chairs). This
was increased if the model showed that there were more than 6 people in the waiting room,
this included patients waiting to have an examination or waiting for results, plus companions.
Each person in the waiting room needs 1.5 m2, this allows for a comfortable space even
when there are higher than normal numbers [13]. It was assumed that at least half of the
patients bring a companion. The CR reader has a footprint area of 2 m2. The X-ray room
had at least two changing cubicles (one for disabled patients), plus space for basket with
gowns (total 8 m2).
There is a cost for departments with longer queues in terms of increased space allocation for
the waiting room. However, in addition to this, some hospitals will fine departments for
patients waiting over a certain time [5]. In this model a fine has not been included for patient
waiting time exceeding a certain period. Once the examination, booking-in and changing
time are all included, the time in the X-ray department should be less than one hour. It is
reasonable that patients’ expectations for a walk-in service are a short wait time. In addition,
the chest examination may be one of many examinations that a patient needs during the
hospital visit. So for both of these reasons it is important to keep the wait time to a minimum.
Very few consumables are used in digital chest imaging: wipes, gloves, hand washing and
gown washing. These costs are small but have been given a nominal value of 10p per
patient.
CEP 07011: 2007
Appendix 1: Cost estimates
28
Image storage costs should be similar for both technologies, both for the physical storage
costs and the staff administration times. Avrin et al [14] estimated the storage costs for a
mammography image to be $0.55, without staff time. Therefore, a nominal charge of £1 per
image has been used.
CEP 07011: 2007
Appendix 2: Processes for CR and DDR
Booking in process for CR and DDR
Request Referral
Appointment / Walk in service / in patient
Reception / Booking
Changing room
Waiting room
CEP 07011: 2007
29
Appendix 2: Processes for CR and DDR
30
Workflow for chest imaging with CR
Call patient / identity check
Prepare room with patient in room
(normal)
Insert CR cassette
Position patient
(with explanation)
Position X-ray unit
Collimate
Select exam
Expose
Remove cassette
Low throughput
Medium/ High Throughput
Very high throughput
Leave patient in room
Read IP
One radiographer leapfrogging
Two radiographers leapfrogging
Accept image
Reject image
Send patient to waiting room
Read IP
Send patient to waiting room
Other radiographer with next patient
Release patient
Repeat X-ray
Confirm previous image
Read IP
Call next patient
Release patient
once accepted
Accept image
Reject image
Accept image
Reject image
Release patient
Call next patient
Recall previous patient
Release patient
Recall patient
wait for room to be empty
Call next patient
wait for room to be empty
Definition of radiographer leapfrogging
Leapfrogging is the process of interspersing imaging of patients. Following the imaging of
one patient, the patient is sent to the waiting room. The operator then puts the cassettes into
the reader. Whilst the reader is scanning the image plates, the operator images the next
patient. When the operator returns to the reader with the next patient’s cassettes, they will
check if the images from the previous patient are acceptable or need to be repeated. The
operator will then either release or re-image the patient.
Two operators leapfrogging is similar. While one operator is reading the cassettes and
confirming the image, the other operator is using the room for imaging the next patient. The
use of the room is thus maximised at the cost of using an extra operator.
CEP 07011: 2007
Appendix 2: Processes for CR and DDR
Workflow for chest imaging with DDR
Call patient / identity check
Call up worklist
Position patient
(with explanation)
Position X-ray unit
Collimate
Exam selected from worklist
Expose
Image at workstation
Leave patient in room
Accept image
Reject image
Release patient
Adjust patient /
Collimation
Call next patient
Repeat X-ray
Release patient
once accepted
CEP 07011: 2007
31
Author and report information
Cost effectiveness of direct
digital radiography versus
computed radiography for
chest radiographer
32
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A Mackenzie, DP Emerton,
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KCARE
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UK
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Email: info@kcare.co.uk
www.kcare.co.uk
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Email: cep@pasa.nhs.uk
www.pasa.nhs.uk/cep
About CEP
The Centre for Evidence-based
Purchasing (CEP) is part of the Policy and
Innovation Directorate of the NHS
Purchasing and Supply Agency. We
underpin purchasing decisions by
providing objective evidence to support the
uptake of useful, safe and innovative
products and related procedures in health
and social care.
We are here to help you make informed
purchasing decisions by gathering
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CEP 07011: 2007
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