Oral Radiol (2004) 20:15–21 DOI 10.1007/s11282-004-0010-3
© Japanese Society for Oral and Maxillofacial Radiology and Springer-Verlag Tokyo 2004
ORIGINAL ARTICLE Takehito Sasaki · Minoru Fujita · Tsuguhisa Katoh Kaoru Kobayashi · Tomohiro Okano · Kenji Sato Shinichi Wada
Current status of diagnostic imaging in dental university hospitals in Japan
Received: January 13, 2004 / Accepted: March 6, 2004
Abstract The diagnostic imaging examinations in all 29 dental university hospitals in Japan were analyzed during a 1-year period from April 1999 to March 2000. The total number of patients examined was 790 859, which corresponded to 27 271 patients per hospital on average, with a range from 7872 to 62 904. Relative to the total number of patients, intraoral radiography was found to have been most frequently performed, 59% on average, with a range from 40% to 80%, depending on the hospital. Extraoral radiography, mostly panoramic radiography, was 36% on average with the range from 18% to 56%. A significant inverse correlation was observed between the percentages of intraoral and extraoral radiography, relative to the total number of all types of imaging examinaT. Sasaki (*) Oral and Maxillofacial Radiology, Tokyo Medical and Dental University, Graduate School, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan E-mail:
[email protected] M. Fujita Department of Oral and Maxillofacial Radiology, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan T. Katoh Tokyo Metropolitan University of Health Sciences, School of Radiologic Science, Tokyo, Japan K. Kobayashi Department of Oral Radiology, Tsurumi University School of Dental Medicine, Yokohama, Japan T. Okano Department of Oral Radiology, Showa University School of Dentistry, Tokyo, Japan K. Sato Department of Oral and Maxillofacial Radiology, The Nippon Dental University, School of Dentistry at Tokyo, Tokyo, Japan S. Wada Department of Radiological Sciences, School of Health Sciences, Niigata University, Niigata, Japan A report from the Radiation Protection Committee (Chairperson, T. Sasaki), Japanese Society for Oral and Maxillofacial Radiology. A portion of this study was presented at the 4th ACOMFR, June 16, 2002, Kaohsiung, Taiwan.
tions. Computed tomography (CT) examinations were performed with their own apparatuses in 27 hospitals with a frequency of 2.9% of patients in all imaging examinations on average and 9.1% at maximum. The scanning parameter of milliampere seconds (mAs) for individual types of routinely performed CT examinations varied widely, and thus the patient dose can be expected to be considerably reduced, without reducing the amount of diagnostic information to be obtained. Other imaging examinations performed were magnetic resonance imaging in 11 hospitals, X-ray fluoroscopy in 8 hospitals, ultrasonography in 20, nuclear medicine in 5, and bone densitometry in 1 hospital. Key words Dental university hospital · Radiation protection · Intraoral · Panoramic · CT
Introduction It is well known that dental radiography is one of the most frequently performed types of radiographic examinations in all medical and dental radiography.1 This is the case in general dental clinics in Japan.1,2 Extraoral radiography, mainly panoramic radiography, has also been widely used in general dental clinics.2 However, more advanced imaging modalities, including fluoroscopy, computed tomography (CT), ultrasonography (US), magnetic resonance imaging (MRI), nuclear medicine, and bone densitometry are also used in dental university hospitals. In fact, CT is widely used in most dental university hospitals in Japan, and CT examinations are routinely performed to diagnose a wide variety of oral and maxillofacial diseases, and also for treatment planning for dental implants. Despite the widespread use of these advanced imaging modalities, no data have yet been reported on the frequency with which examinations using these modalities are actually performed in dental university hospitals in Japan. The purpose of this study, therefore, was to obtain data on the frequencies of imaging examinations using both conventional radiography and advanced imaging modalities.
16 Table 1. Number of patients receiving imaging examinations in 29 dental university hospitals in Japan from April 1999 to March 2000 Modality
Intraoral Extraoral Fluoroscopy CT US MRI Nuclear medicine Bone densitometry All modalities combined
Patients/hospital
% Patients
Total in Japan
mean
range
mean
range
16 091 9 873 55 740 246 237 26 4 27 271
5 412–42 792 2 460–24 995 0–224 0–1850 0–845 0–1428 0–236 0–101 7 872–62 904
58.9 36.1 0.2 2.9 1 0.8 0.1 0.01 100
39.7–80.1 18.2–56.4 0–1.0 0.0–9.1 0.0–3.8 0.0–5.4 0.0–2.0 0–0.4
466 634 286 330 1 586 21 448 7 141 6 862 757 101 790 859
Of the 29 dental university hospitals surveyed, imaging examinations were performed with X-ray fluoroscopy in 8 hospitals, CT in 27, ultrasonography in 20, MRI in 11, nuclear medicine in five, and bone densitometry in one hospital CT, computed tomography; MRI, magnetic resonance imaging; US, ultrasonography
Table 2. Number of exposures from imaging examinations in 29 dental university hospitals in Japan from April 1999 to March 2000 Modality
Intraoral Extraoral Fluoroscopy CT US MRI Nuclear medicine Bone densitometry All modalities combined
Exposures/hospital
% Exposures
Mean
Range
mean
range
35 728 19 719 55 1 181 246 1 075 26 7 58 037
11 976–108 000 4 836–67 355 0–224 0–4 666 0–845 0–7 621 0–236 0–197 16 812–156 793
62.2 33.7 0.1 2 0.4 1.5 0.1 0.01 100
38.1–85.9 12.9–59.6 0–0.6 0.0–8.6 0.0–1.6 0.0–11.6 0.0–0.6 0.0–0.4
Since CT is becoming a major radiation source in medical radiology examinations,1 it is important to determine the relative dose contribution by CT examination compared with the total population dose in dentistry. In this study, both the frequency and technological parameters of CT scanning were surveyed, since these parameters are the major factors determining the patient dose in CT scanning. These data may be useful as a measure of the relative contribution of radiation dose by CT examination to the total population dose in university dental hospitals.
Methods and materials The Radiation Protection Committee of the Japanese Society for Oral and Maxillofacial Radiology sent out questionnaires on the frequency of use of all types of imaging modalities and the technological parameters of CT scanning to dental university hospitals, and received answers from all 29 hospitals in Japan. The items surveyed were (1) the number of patients examined using each type of imaging modality used in the hospital; (2) the number of exposures or films of all types of radiography performed, and the number of series of sec-
Total in Japan 1 036 112 571 860 1586 34 257 7 141 31 176 757 197 1 683 086
tional imagings performed for CT, ultrasonography, and MRI examinations; (3) the type of CT scanners used; and (4) the scanning parameters of the CT examinations. This survey covered a 1-year period from April 1999 to March 2000. All answers received were carefully inspected, and the questionnaires were then sent again to a chief radiological technologist, who checked and verified any erroneous or unusual descriptions received. The observed variables were classified into six subgroups with equal grouping intervals. The frequencies are shown in the figures both in terms of the number of hospitals and as the cumulative relative frequency (%) for the six subgroups of each observed variable.
Results The number of patients and exposures or images reported by all 29 hospitals is summarized in Tables 1 and 2, respectively. The number of series of images that were taken, as opposed to the number of single images, is shown for fluoroscopy, CT, MRI, nuclear medicine, and bone densitometry in Table 2. The total number of patients examined in all 29 hospitals was 790 859, which corresponds to 27 271 pa-
17
Frequency Cumulative %
10
100
8
80
6
60
4
40
Cumulative (%)
120
Number of hospitals
12
Cumulative (%)
Number of hospitals
Frequency Cumulative %
0– 2 460
2
20
0
0
2 461– 6 967
6 968– 11 474
11 475– 15 981
15 982– 20 489– 20 488 24 995
Number of patients per hospital Fig. 2. Frequency distribution of the number of patients receiving extraoral radiography per hospital
5 413– 12 889– 20 365– 27 841– 35 317– 0– 5 412 12 888 20 364 27 840 35 316 42 792
Number of patients per hospital
Cumulative (%)
tients per hospital on average, with a range from 7872 to 62 904, depending on the hospital. Intraoral radiography was the most frequently performed modality. However, extraoral radiography, in particular, panoramic radiography, was the most frequent type of radiography performed in some hospitals, accounting for up to 56% and 60% of the total number of patients and exposures, respectively. CT examinations were routinely performed in most hospitals. The total number of patients receiving CT examinations was 21 448 in 27 hospitals, and none in only two hospitals. The numbers per hospital ranged from 307 to 1850, with a mean of 800 patients per hospital in the 27 hospitals. The mean was 740 averaged over 29 hospitals, as shown in Table 1. The percentage of patients receiving CT examinations ranged from 0.8% to 9.1%, with a mean of 3.0%, relative to the total number of patients receiving all types of imaging, as averaged for the 27 hospitals. The mean value was 2.7% averaged over 29 hospitals. MRI examinations were performed for a total of 6862 patients in 11 hospitals, with a range from 92 to 1428 patients and a mean of 624 patients per hospital. The percentage of patients receiving MRI examinations varied widely among the hospitals, from a minimum of 0.4% to a maximum of 5.4%, with a mean of 2.2% averaged over the 11 hospitals. Other imaging examinations performed were Xray fluoroscopy in 8 hospitals, ultrasonography in 20 hospitals, nuclear medicine in 5, and bone densitometry in 1 hospital. The number of patients receiving intraoral radiography per hospital ranged from a minimum of 5412 to a maximum
Number of hospitals
Fig. 1. Frequency distribution of the number of patients receiving intraoral radiography per hospital
0– 39.7
39.8– 47.8
47.9– 55.9
56.0– 64.0
64.1– 72.1
72.2– 80.1
Intraoral radiography patients (%) Fig. 3. Frequency distribution of the proportion of the number of patients receiving intraoral radiography compared with all imaging techniques for individual hospitals
of 42 792, with a mean of 16 091 patients (Fig. 1). The number of patients receiving extraoral radiography per hospital ranged from a minimum of 2460 to a maximum of 24 995, with a mean of 9873 patients. The proportion of patients who received intraoral radiography relative to the total number of patients for all types of imaging ranged from 39.7% to 80.1%, depending on the hospital, with a mean of 58.9% (Fig. 3). The proportion of patients receiving extraoral radiography relative to the total number of patients receiving all types of imaging ranged from 18.2% to
Cumulative (%)
Number of hospitals
Cumulative (%)
Number of hospitals
18
0– 4 836
0– 18.2
18.3– 25.9– 25.8 33.5
33.6– 41.2– 41.1 48.8
4 837– 17 341– 29 845– 42 348– 54 852– 17 340 29 844 42 347 54 851 67 355
Number of exposures per hospital
48.9– 56.4
Fig. 6. Frequency distribution of the number of exposures or films used for extraoral radiography per hospital
Extraoral radiography patients (%)
Cumulative (%)
Number of hospitals
Cumulative (%)
Number of hospitals
Fig. 4. Frequency distribution of the proportion of the number of patients receiving extraoral radiography for individual hospitals
0– 38.1
38.2– 47.7
47.8– 57.2
57.3– 66.8
66.9– 76.3
76.4– 85.9
Intraoral radiography exposures (%) 0– 11 977– 31 182– 50 387– 69 591– 88 796– 11 976 31 181 50 386 69 590 88 795 108 000
Number of exposures per hospital Fig. 5. Frequency distribution of the number of exposures or films used for intraoral radiography per hospital
56.4%, depending on the hospital, with a mean of 36.1% (Fig. 4). The number of exposures or films used in intraoral radiography and extraoral radiography per hospital is shown in Figs. 5 and 6, respectively. The number of intraoral radiographic films or exposures taken per hospital ranged from a minimum of 11 976 to a maximum of 108 000, with the maximum number being nine times greater than
Fig. 7. Frequency distribution of the proportion of the number of exposures or films used in intraoral radiography compared with all exposures used in all imaging methods for individual hospitals
the minimum. The number of extraoral radiographic films taken per hospital ranged from a minimum of 4836 to a maximum of 67 335, with the maximum being 14 times greater than the minimums. The proportion of intraoral radiographic films relative to the total number of all types of imaging examinations ranged from 38% to 86%, depending on the hospital, with a mean of 62% (Fig. 7). The proportion of extraoral radiographic films, mostly panoramic radiography, ranged from 13% to 60%, depending on the hospital, and with a mean of 34% (Fig. 8). The percentage
19
ness, number of slices per rotation, and table speed (mm per rotation) were surveyed. From these parameters, a measure of the patient dose per scan at a given point in the radiation field, expressed as milliampere seconds (mAs) per scan was calculated; these values are shown in Table 3, together with the tube voltage. It should be noted here that the tube voltages varied little among the CT scanners in each CT examination subgroup, and no significant difference was noted among the subgroups. In contrast, the mAs per scan varied widely among the CT scanners within each subgroup. However, again no significant difference was noted among the CT examination subgroups.
Discussion
Extraoral radiography (%) films
The present survey has provided, for the first time to our knowledge, reliable data on the frequency with which all types of imaging examinations are actually performed in dental university hospitals in Japan. Intraoral radiography was the most frequent procedure, but its frequency of use
Cumulative (%)
Number of hospitals
of extraoral radiography was inversely correlated with the percentage of intraoral radiography on the basis of the number of films taken, with the correlation coefficient r ⫽ 0.980 (Fig. 9). A similar relationship was also found between the number of patients receiving extraoral radiography and those receiving intraoral radiography (data not shown). There are a total of 32 CT scanners in the 27 hospitals in Japan; five hospitals have two scanners each and 22 hospitals have one scanner each. More advanced types of CT apparatuses were found in some of the hospitals. Fifteen helical and six multidetector scanners were used, compared to 11 sequential types of scanners; the helical and multidetector scanners accounted for 66% (21/32) of all apparatuses. The CT examinations routinely performed in dental university hospitals can be grouped into five types: plain CT for soft-tissue mode; plain CT for bone mode; contrast-enhanced CT; dental CT for dental implants; and 3-D CT. The most frequently used scanning parameters for tube voltage, tube current, seconds per rotation, slice thick-
0– 12.9
13.0– 22.3
22.4– 31.7– 31.6 40.9
41.0– 50.3
–
50.4– 59.6
Intraotal radiography (%) films
Extraoral radiography exposures (%) Fig. 8. Frequency distribution of the proportion of the number of exposures or films used in extraoral radiography for individual hospitals
Fig. 9. Correlation between the proportions of the number of films used for introral and extraoral radiography relative to the total number of films used in all imaging performed in all hospitals
Table 3. Tube voltage and mAs per scan Type of CT examination
Number of apparatuses
Tube voltage (kV) mean ⫾ SD (range)
mAs per scana mean ⫾ SD (range)
Plain CT for soft-tissue mode Plain CT for bone mode Contrast-enhanced CT Dental CT for dental implants 3D CT
32 32 31 30 29
122 ⫾ 6 (110–140) 122 ⫾ 7 (110–140) 122 ⫾ 22 (110–140) 123 ⫾ 31 (110–140) 122 ⫾ 36 (110–140)
293 250 257 169 196
⫾ 266 (65–1250) ⫾ 221 (43–1000) ⫾ 212 (65–1000) ⫾ 167 (50–1000) ⫾ 201 (21–1000)
3D, three-dimensional a mAs per scan determined from tube current (mA), seconds per rotation, slice thickness (mm), number of slices per rotation, and table speed (mm per rotation)
20
varied among hospitals. It was used in from 38% to 86% of all examinations conducted, based on the number of films, and in from 40% to 80% of all examinations, based on the number of patients in all imaging examinations. The frequency of extraoral radiography examinations, mostly panoramic radiography, ranged from 13% to 60% based on the number of films. A significant inverse correlation was observed between the number of films used for intraoral and the number used for extraoral radiographs, relative to the number used in all imaging examinations (Fig. 9). This evidence strongly suggests that the patient selection criteria for individual imaging modalities differ significantly among hospitals. Recently, CT has become a frequently used imaging modality, as indicated by an UNSCEAR report on health care level I countries.1 The annual number of X-ray examinations in these countries indicated that general radiography, including radiography for the chest, limbs, and joints, accounted for about 50% of all X-ray examinations, and CT accounted for only 6%. However, it has been estimated that in these countries the collective dose of radiation by CT represents a major part of the radiation received from all types of X-ray examinations, accounting for 41% of the total radiation dose, based on data for 1991–1996.1,3 It is important to note that CT examinations now account for about 15% of all X-ray examinations, and for about 70% of the dose of radiation at some universities in the United States.4 A similar analysis that included dental radiography was carried out in 1998 in Switzerland. There, general radiography examinations annually accounted for 48% of all Xray examinations, and CT accounted for 3.4%, with dental radiography alone accounting for 43%.5 Although the proportion of the dose from general radiography was 41%, the dose from CT accounted for 28%, and that from dental radiography for 1%.5 The number of CT scanners per million people in Japan has been reported to be the highest in the world.1 However, no data are available on the number of CT scanners in dental hospitals, or on the number of CT examinations performed in those hospitals. Although CT examinations are sometimes requested by dental and oral surgery departments in general hospitals, and those patients are referred to general radiology departments in those hospitals, the frequency with which this occurs is not known. The present study showed that CT examinations are routinely performed in most dental hospitals, and that their frequency is increasing. At most, 9% of patients are receiving CT examinations. Although MRI examinations were still limited to 11 hospitals at the time this study was conducted, their frequency was increasing as well and accounted for as much as 5% of the total number of patients. Contrast this with the situation in all Japanese dental clinics, including most general dental practitioners, during the same period; the frequency of intraoral radiography and panoramic radiography was estimated as 85% and 14%, respectively, based on the number of films, and the two together accounted for 99%.2 CT and MRI examinations together accounted for less than 0.1% of X-ray examinations in all Japanese dental clinics.2
The patient dose from CT examinations has become a major concern in terms of protecting patients against excessive medical radiation exposure. It has been recommended that the scanning parameters be optimized to individual patients.3 Since the major factors affecting patient dose are the size of the scanning area, the tube voltage, and the mAs, the tube voltage and several factors that affect the mAs were surveyed in the present study for adult patients receiving five routinely used types of examinations. The mAs per scan derived from these factors was significantly different among the CT scanners by a factor of up to about 20 for four types of CT examinations, but by a factor of 50 for 3-D CT. Tube voltage varied narrowly among CT scanners. Since the size of the scanning area within the CT examination subgroups was apparently similar, the variation in mAs per scan may be roughly proportional to that in patient dose. One of the CT scanners showing the highest mAs per scan was an old, sequential type of scanner, which operated with a tube current of 250 mA and 4 s per rotation, resulting in a value of 1000 mAs per scan. With this particular scanner, the dose is mainly determined by the specifications of the apparatus, and it may not be possible for the operator to adjust it. However, in most scanners, the mAs is controllable according to the clinical requirements of the examination.3 This fact was recently emphasized for pediatric patients,6,7 and a practical method to reduce the patient dose has been recommended.8 The Internation Commission on Radiological Protection (ICRP) has been preparing to incorporate the concept of diagnostic reference level (DRL) as a guide for the optimization of radiation protection during medical exposure.9,10 ICRP Committee 3 has provided an example of the DRL used in a specified medical imaging protocol, and the mAs for a specific CT protocol with a specific clinical purpose, along with the type of equipment, technique factors, and patient characteristics.10 The data obtained in our study may thus indicate that the dose can be significantly reduced by selective setting of the scanning parameters, without reducing the amount of diagnostic information gathered and needed by the clinician. The recent introduction of 3-D volume imaging and cone beam volume computed tomography, developed specifically for oral and maxillofacial imaging, has provided 3-D sectional images with a higher spatial resolution, and with a lower radiation dose, but the volume for the imaging is limited compared to that with conventional CT.11–13 The selection criteria of dental patients for either conventional CT or cone beam volume CT are certainly important from the viewpoint not only of radiation protection, but also of CT efficacy in dentistry. Further research for that purpose is needed to establish more efficient radiological imaging in dentistry.
References 1. United Nations Scientific Committee on the Effects of Atomic Radiation. Sources and effects of ionizing radiation. UNSCEAR 2000 Report. Volume 1; Sources. New York: United Nations; 2000.
21 2. Shimano T, Suzuki Y, Sasaki T. Long-term trend of dental radiographic examinations in Japan: analysis on health insurance data. Dent Radiol 2002;42:9–21. 3. ICRP [International Commission on Radiological Protection] Managing patient dose in computed tomography. Annals of ICRP. Publication 87. Amsterdam: Elsevier; 2001. 4. Mettler FA Jr. X-ray dose in medicine overview. National Council on Radiation Protection and Measurements Symposium. National Conference on Dose Reduction in CT with an Emphasis on Pediatric Patients, AJR 2003;321–9. 5. Aroua A, Burnand B, Decka I, Vader JP, Valley JF. Nation-wide survey on radiation doses in diagnostic and interventional radiology in Switzerland in 1998. Health Phys 2002;83:46–55. 6. Brenner DJ, Elliston CD, Hall EJ, Berdon WE. Estimated risk of radiation induced fatal cancer from pediatric CT. AJR 2001;176: 289–96. 7. Rogers LF. From the editor’s notebook. Taking care of children: check out the parameters used for helical CT. AJR 2001;176:287.
8. Donnelly LF, Emery KH, Brody AS, Loar T, Gylys-Morin VM, Anton CG, et al. Minimizing radiation dose for pediatric body applications of single-detector helical CT: strategies at a large children’s hospital. AJR 2001;176:3003–6. 9. ICRP. A report on progress towards new recommendations: a communication from the International Commission on Radiation Protection. J Radiol Prot 2001;21:113–23. 10. ICRP Committee 3. Diagnostic reference levels in medical imaging: review and additional advice. www.icrp.org/docs/DRL_for_ web.pdf 11. Mozzo P, Procacci C, Tacconi A, Martini PT, Andreis IA. A new volumetric CT machine for dental imaging based on the conebeam technique: preliminary results. Eur Radiol 1998;8:1558–64. 12. Arai Y, Tammisalo E, Iwai K, Hashimoto K, Shinoda K. Development of a compact computed tomographic apparatus for dental use. Dentomaxillofac Radiol 1999;28:245–8. 13. Heiland M, Schulze D, Adam G, Schmelzle R. 3D-imaging of the facial skelton with an isocentric mobile C-arm system (Siremobil Iso-C3D). Dentomaxillofac Radiol 2003;32:21–5.
