British Journal of Radiology (2004) 77, 597-599
© 2004 British Institute of Radiology
doi: 10.1259/bjr/54198101
Application of low dose rate pulsed fluoroscopy in cardiac pacing and electrophysiology: patient dose and image quality implications
C J Kotre, PhD
1
S Charlton, DCR(R)
2
K J Robson, PhD
1
I P Birch, MSc
1
S P Willis, DCR(R)
1 and
M Thornley, MSc
1
1 Regional Medical Physics Department, Newcastle General Hospital, Newcastle-upon-Tyne, NE4 6BE and 2 Cardiology X-ray Department, Freeman Hospital, Newcastle-upon-Tyne NE7 7DN, UK
 |
Abstract
|
|---|
The performance of a low dose rate pulsed fluoroscopy option and its successful application to cardiac pacing and electrophysiology is reported. Low dose rate 6.25 frames per second pulsed fluoroscopy was made available in two catheter laboratories at a specialist cardiac centre in February 2003, and was adopted as the standard imaging technique for cardiac pacing procedures. The image quality was found to be considerably poorer than conventional modern units, being very similar to that which would have been accepted as adequate performance 20 years ago, but at less than one-tenth of the dose rate. No problems with the clinical acceptance of this imaging mode for cardiac pacing and electrophysiology have been reported. The already low median patient dose–area product for pacing at this cardiac centre was further reduced by 50% with the introduction of this fluoroscopy option.
|
Introduction
|
|---|
It is a requirement of the Ionising Radiation (Medical Exposure) Regulations 2000 [1] that radiation doses to patients undergoing radiological procedures "are kept as low as reasonably practicable consistent with the intended purpose". This philosophy of optimization has been widely accepted for many years. It is, however, relatively rare in general radiology that an examination protocol is selected that intentionally sacrifices image quality in order to reduce patient dose. Clearly, the types of examination where this strategy is acceptable are limited to those where the requirement is only to adequately distinguish high contrast features. Procedures which could be considered to be in this category are cardiac pacing and electrophysiology. In these procedures pacing or electrophysiology wires are inserted via an artery or vein and guided into the heart using fluoroscopy and electrocardiographic monitoring.
|
Equipment performance
|
|---|
This report relates to the use of two Siemens Coroskop units in a dedicated cardiology suite. The units feature a "Fluoro+" option, which on commissioning is set as a high dose fluoroscopy program. This feature had been largely redundant, and the decision was taken to re-program it for 6.25 frames per second pulsed fluoroscopy at a significantly lower dose rate than the default 6.25 frames per second setting, to be used where high image quality was not an absolute requirement. The default 6.25 frames per second pulsed setting was left unchanged and is still selectable on the units. The intensifier input dose rates, measured using a 1.5 mm copper filter, and the patient skin entrance dose rates, measured using a 20 cm Perspex phantom (70 cm focus–chamber distance), are tabulated in Table 1
for the three field sizes available on these units. The intensifier input dose rates for the low dose option required readings at the last significant digit of the dosemeter, making these small values more subject to uncertainty. In common with most dedicated cardiology units, the field sizes are set up "overframed" as rectangular images, so the magnified fields correspond to quite small radiation field sizes.
View this table:
[in this window]
[in a new window]
|
Table 1. Image intensifier input dose rates for the default 6.25 frames per second pulsed fluoroscopy setting, and the re-programmed low dose rate option, measured using a 1.5 mm copper filter, and the corresponding patient skin entrance dose rates, measured at the surface of a 20 cm Perspex phantom for the three image field sizes available
|
|
Figure 1 shows the threshold contrast-detail diameter performance of one of the units operated in automatic dose rate mode with a 1.5 mm copper filter for the 23 cm field size. This is a standard test of image intensifier imaging performance [2]. The performance of the unit is shown as a solid line, with the performance expected for standard modern units [3] given by the long-dashed line. As expected, the re-programmed Fluoro+ option gives a significantly poorer (noisier) image than the standard modern units. Also shown on the figure as a short-dashed line is the performance standard quoted for acceptable image intensifier performance at 0.26 µGy s–1 in 1982 [4]. Interestingly, the performance for the re-programmed Fluoro+ option is almost identical to this old standard, but at less than 10% of the dose rate on which that standard was based.
View larger version (11K):
[in this window]
[in a new window]
|
Figure 1. Threshold contrast-detail diameter curve measured for the re-programmed low dose rate pulsed fluoroscopy mode (solid line) compared with the expected performance for standard fluoroscopy systems [3] (long dashes) and an earlier standard [4] (short dashes). The performance for the low dose rate option is almost identical to this old standard, but at less than 10% of the dose rate on which that standard was based.
|
|
|
Patient dose results
|
|---|
At the time of reporting, only one of the two rooms was fitted with a dose–area product (DAP) meter from which data can be recorded directly. The DAP results in this room are routinely recorded for each patient and periodically returned on disk to the Regional Medical Physics Department for collation and comparison with other centres in the North of England. Few electrophysiology procedures were carried out in this particular room so DAP results are reported for cardiac pacing only. The calibration of DAP meters and dosemeters used above is traceable to national standards.
Table 2 shows the pooled DAP results for the six cardiologists regularly performing pacing at this centre using this equipment, before and after the Fluoro+ option was re-programmed in February 2003. A 50% reduction in median DAP can be seen, with no significant change in the median screening time for the procedure. It is also noteworthy that at this centre the typical doses for this procedure were already low, compared with the previously established regional (North of England) median value, which is also given in Table 2. After introduction of the re-programmed low dose rate Fluoro+ option for cardiac pacing, the median DAP results fell to 20% of the regional median value.
View this table:
[in this window]
[in a new window]
|
Table 2. Dose–area product (DAP) and screening times for cardiac pacing procedures before and after the introduction of the re-programmed low dose rate mode of pulsed fluoroscopy, compared with the previously established averaged regional values for the same procedure
|
|
|
Clinical acceptability
|
|---|
As more complex and technically challenging procedures such as internal cardiac defibrillators, bi-ventricular pacing and radiofrequency ablation with their often lengthy fluoroscopy times, are being performed at specialist cardiology centres, cardiologists and radiographers are becoming increasingly aware of the need to reduce radiation exposure to patients and staff. The low dose rate fluoroscopy program matched with a digital pulsed fluoroscopy rate of 6.25 frames per second results in reduced image quality. It is, however, adequate to show easily visualized pacing and electrophysiology wires. Once it had been demonstrated that there was a significant reduction in DAP readings, the low dose technique was universally accepted by the clinicians.
|
Conclusions
|
|---|
For fluoroscopic examinations where high image quality (signal-to-noise ratio) is known to be unnecessary for the successful outcome of the procedure, it is possible to employ very low patient dose rates. To take full advantage of this approach, however, it may be useful to employ pulsed fluoroscopy with dose rates lower than those available as standard settings on most fluoroscopy units. The performance of a low dose rate pulsed fluoroscopy option and its successful application to cardiac pacing and electrophysiology has been reported. The already low median patient DAP for cardiac pacing at this specialist centre was further reduced by 50% with the introduction of this approach.
Received for publication January 5, 2004.
Revision received March 19, 2004.
Accepted for publication April 15, 2004.
|
References
|
|---|
- The Ionising Radiation (Medical Exposure) Regulations 2000. London: HMSO, 2000.
- IPEM. Recommended standards for the routine performance testing of diagnostic X-ray imaging systems. Institute of Physics and Engineering in Medicine Report No. 77. York: IPEM, 1997.
- MDD. The testing of X-ray image intensifier-television systems. Medical Devices Directorate Evaluation Report MDD/94/07. London: Department of Health, 1994.
- DHSS. The testing of X-ray image intensifier-television systems. Working Group Report STB/7/82. London: Department of Health, 1982.
Top
Abstract
Introduction
