A Computerized Automatic Exposure Device For Chest Radiography in Infants 1,4 Tetsurow Umezawa, M.D. Yasushi Suganuma, M.D.2 Kikuo Kowada 3,5 3 Yasushi Matsuki, M.D. Takatoshi Kitamura, M.D. 2
Introduction ccurate chest
or
radiographs
obtained during inspiration
expiration are importantt
in clinical diagnosis. However, it is difficult to take such radiographs in infants because of their inability to cooperate. Our automatic exposure device was designed to obtain better chest radiographs in infants.
Materials and Methods Our automatic exposure device is composed of three parts: 1) a mask with a pressure sensor (Nihon Koden, TP-603T); 2) a com-
puter system (NEC, PC-9801 CV) ; analyzes intramask pressure signals; and 3) an exposure device
which
1
Department of Pediatrics Department of Pediatric Surgery 3 Division of Radiology Metropolitan Hachioji Children’s Hospital 2
4
Hachioji, Tokyo, Japan Department of Pediatrics University Hospital, Teiko University School of Medicine
Kanagawa, Japan Kawasaki, 5 Division of Radiology
Metropolitan Fuchu Hospital Fuchu, Tokyo, Japan Address correspondence to: Yasushi Suganuma, M.D., Department of Pediatric Surgery, Metropolitan Hachioji Children’s Hospital, 4-33-13 Daimachi, Hachioji,
Tokyo, 193, Japan
(Shimazu Seisakusho, HD-150G60). Computer software was written in the programming language Nsg-BASIG(86) (NEC Corporation and Microsoft Gorporation). At the time of examination, the patient is placed on an immobilization board and held in the upright position. A small mask with a pressure sensor is placed over the patient’s face. A computer system analyzes intramask pressure signals, converted from analog to digital (50 samples/sec), for nine seconds and calculates the absolute value of the difference (D) between maximum negative pressure (inspiration) and maximum positive pressure (expiration). The
computer system judges an inspiratory phase appropriate when the intramask pressure measures a maximum negative pressure of +D/4. Just after the negative peak of the inspiratory phase is reached, the computer system sends a signal to the exposure device (approximately 40 msec after the peak), and the exposure is taken automatically. This exposure point was determined from our previous study with fluoroscopy, which showed that the change in intramask pressures is somewhat delayed by the diaphragm’s rhythmical movement (about a 50-msec delay when the infant is crying and a 200-msec delay when the infant is not crying). The nine-second initial moni-
toring of intramask pressures was also determined from our previous study; if needed, 10 seconds or more can be programmed. A long monitoring time allows for detection of a greater negative respiratory pressure (deeper inspiration), but it also requires a longer wait for the subsequent exposure. For this study, we selected only chest radiographs taken for preoperative examination in planned surgical patients 1 month to 18 months old. A total of 350 radiographs met our selection criteria between September 1989 and March 1990. These radiographs were taken randomly, either with the automatic exposure device or manually by skilled technicians, and the successful exposure rates of these methods were compared by dividing the patients into three age groups: 1) from 1 to 6 months old, 2) from 7 to 12 months old, and 3) from 13 to 18 months old. We judged the radiographs to be successful when the left diaphragm line was on the left posterior ninth rib or below. Statistical analysis was performed using the chi-square test, and a P value of
Introduction ccurate chest
or
radiographs
obtained during inspiration
expiration are importantt
in clinical diagnosis. However, it is difficult to take such radiographs in infants because of their inability to cooperate. Our automatic exposure device was designed to obtain better chest radiographs in infants.
Materials and Methods Our automatic exposure device is composed of three parts: 1) a mask with a pressure sensor (Nihon Koden, TP-603T); 2) a com-
puter system (NEC, PC-9801 CV) ; analyzes intramask pressure signals; and 3) an exposure device
which
1
Department of Pediatrics Department of Pediatric Surgery 3 Division of Radiology Metropolitan Hachioji Children’s Hospital 2
4
Hachioji, Tokyo, Japan Department of Pediatrics University Hospital, Teiko University School of Medicine
Kanagawa, Japan Kawasaki, 5 Division of Radiology
Metropolitan Fuchu Hospital Fuchu, Tokyo, Japan Address correspondence to: Yasushi Suganuma, M.D., Department of Pediatric Surgery, Metropolitan Hachioji Children’s Hospital, 4-33-13 Daimachi, Hachioji,
Tokyo, 193, Japan
(Shimazu Seisakusho, HD-150G60). Computer software was written in the programming language Nsg-BASIG(86) (NEC Corporation and Microsoft Gorporation). At the time of examination, the patient is placed on an immobilization board and held in the upright position. A small mask with a pressure sensor is placed over the patient’s face. A computer system analyzes intramask pressure signals, converted from analog to digital (50 samples/sec), for nine seconds and calculates the absolute value of the difference (D) between maximum negative pressure (inspiration) and maximum positive pressure (expiration). The
computer system judges an inspiratory phase appropriate when the intramask pressure measures a maximum negative pressure of +D/4. Just after the negative peak of the inspiratory phase is reached, the computer system sends a signal to the exposure device (approximately 40 msec after the peak), and the exposure is taken automatically. This exposure point was determined from our previous study with fluoroscopy, which showed that the change in intramask pressures is somewhat delayed by the diaphragm’s rhythmical movement (about a 50-msec delay when the infant is crying and a 200-msec delay when the infant is not crying). The nine-second initial moni-
toring of intramask pressures was also determined from our previous study; if needed, 10 seconds or more can be programmed. A long monitoring time allows for detection of a greater negative respiratory pressure (deeper inspiration), but it also requires a longer wait for the subsequent exposure. For this study, we selected only chest radiographs taken for preoperative examination in planned surgical patients 1 month to 18 months old. A total of 350 radiographs met our selection criteria between September 1989 and March 1990. These radiographs were taken randomly, either with the automatic exposure device or manually by skilled technicians, and the successful exposure rates of these methods were compared by dividing the patients into three age groups: 1) from 1 to 6 months old, 2) from 7 to 12 months old, and 3) from 13 to 18 months old. We judged the radiographs to be successful when the left diaphragm line was on the left posterior ninth rib or below. Statistical analysis was performed using the chi-square test, and a P value of
