Personal-Computer-Made　Drawing of a Kidney Which Moves Back and Forth with Respiration - A Trial to Aid Patient's Understanding of the Ultrasonic Monitor during Extracorporeal Shockwave Lithotripsy

AKIRA KIMURA 1 , KYOICHIRO KAMIYA 2 Department of Urology, University of Tokyo Branch Hospital 1 Department of Urology, Metropolitan Aoyama Hospital 2

running　head: Personal-Computer-Made Schema of the Ultrasonic Monitor Image of Lithotriptor

Key words:Extracorporeal shockwave lithotripsy, Ultrasonic monitoring, Computer-drawn schema, Patient's co-operation

abstract

With extracorporeal shockwave lithotriptors using ultrasonic monitoring for focusing, patients can see the real time ultrasonic images during lithotripsy. With such lithotriptors, patients' co-operation by adjusting their respiration so that the stone stays in the focus of the shock wave will increace the effective shots. For this reason, the patient's understanding of ultrasonic imaging is inevitable. The sketch of a kidney drawn on the CRT of the computer put on a treatment table next to the ultrasonic monitor was useful to aid the patient's understanding of the ultrasonic image.

Introduction

In Metropolitan Aoyama Hospital, more than 200 patients have been treated with ESWL using Toshiba ESL500A since 1992. The ESL-500A, a piezoelectric lithotriptor, has two distinctive features. One of them is that it has an anti-misshot device 1,2) , the Echo Trigger Mode (ETM). In the ETM, low-intensity ultrasonic waves are generated by the piezoelectric ceramic elements, and the intensity of echos from the focal zone is checked to determine whether a stone exists there. Only after the presence of a stone is confirmed, shock waves are generated and transmitted to it automatically. If the echo is too weak to locate the stone, the operator must control the shot, while carefully monitoring the movement of the stone. In the treatment of renal stones or upper-ureteral stones, which are affected by respiratory movement, ETM considerably reduces the operator's workload. Secondly, a sector probe for ultrasonic imaging is incorporated inside of the overhead applicator (a shock wave generator). An operator can see the real time ultrasonic image during the reatment. This helps the operator to decrease the number of misshots and increase the success rate of shots compared to ESWL performed with fluoroscopic monitoring. A patient who is treated in a prone position can also see the real time ultrasonic image during the treatment (Fig.1). This helps the patient to adjust his respiration so that the stone stays in the focus of the shock wave as long as possible. For this purpose, however, the patient's understanding of ultrasonic imaging is inevitable. A drawing of a kidney moving back and forth periodically is made by a personal computer to mimic a real time renal ultrasonic image moving with respiration.

Materials and Methods

A sketch of renal parenchyma, pelvis, and ureter is drawn on the CRT of a book-type personal computer Dynabook. The software is made in BASIC language. The position and the size of a stone is input through the keyboard of the computer (Fig.2). Its position can be settled anywhere in the pelvis or ureter. The schema thus made resembles the intravenous pyelogram of the patient which was taken preoperatively. After the drawing of the stone on the kidney, the sketch begins to move back and forth periodically. A schema, which shows a situation as if the shock wave is generated and transmitted to the focal zone, is also drawn when the stone is in the focal zone (Fig.3). Since May,1994, 30 patients were treated watching the computer-drawn-sketch. These patients had renal stones or upper ureter stones, and were treated on a prone position. With these patients, the usefulness of the sketch was evaluated in two points; whether the schemas which resemble real monitor images cuold be made, and whether they could help patients' understanding.

Results

The personal computer is small enough to put on a treatment table next to the ultrasonic monitor. The schema resembling the real minitor images could be made with all 30 patients whose stones are in the pelvis or upper ureter. It means that this system is useful for any patient who is treated on a prone position and thus can watch the ultrasonic monitor. The range of respiratory movement can be changed, so that the both cases, one being that a stone comes in the focal zone when a patient inspires and another when he expires, can be simulated (Fig.4,5). The speed of the movement can also be changed up to 26 times per minute. This is enough to adjust to anybody's respiration. The sketch drawn on the CRT of the computer was useful to aid the patient's understanding of the ultrasonic monitor image with all 30 patients.

Discussion

At the beginning of the usage of ESL-500A, we thought that as an anti-misshot device would eliminate missed shots, it would not be required that a patient adjust his respiraion to keep the stone in the focal zone as long as possible, watching the ultrasonic monitor. However, after having experienced several cases, we found that the treatment time became markedly prolonged when ETM was chosen, the threshold for Echo-Trigger was set at a sufficiently high level, and a patient was not asked to watch the ultrasonic monitor and adjust his respiration. In ETM with an adequate threshold, the shock wave is not generated when a stone is not in the focus. The pain due to the shock waves is slight but not none. After several shots, patients had learned to hold their respiration so that the stone came out of the focus. When an operator positioned the aplicator so the stone came in the focus during expiration, the patient learned to hold his breath at inspiration. When the aplicator was positioned to adjust to his inspiration, he then held his breath at expiration. As a result, when the threshod of ETM was set at a high level, just one or two shots were generated, i.e., only about ten shots per minute. In order to have a patient adjust his respiration through watching ultrasonic monitor, it is necessary to educate him how the ultrasonic images of his kidney and the stone look like and move with respiration. In general, ultrasonic images are difficult for an amateur to understand compared with CT images or ordinary radiograms,because the contours of organs in ultrasonograms are difficult to trace, especially when the organ is solid, not cystic. The sketch drawn on the CRT of the computer put on a treatment table next to the ultrasonic monitor was useful to aid the patient's understanding of the ultrasonic image with all 30 patients. Perhaps, the fact that the sketch resembles the intravenous pyelogram with which the patient is familiar greatly contributed to the patient's understanding. Although all 30 patients were successfully treated with ETM, the time required for the treatment (average number of shots was 3000) ranged from 25 minutes to 45 minutes, the average being 32 minutes, and was not significantly shorter than that of patients treated with ETM without watching the schema. The reason of this insignificant difference is that there was no decided format among operators in our hospital about the frequency of shots per second and the threshold of ETM. Both can be arbitrary changed. The frequency can be changed from one to three shots per second. The threshold can be lowered as an operator likes, resulting that shock wave is generated even when stones are out of the focal zone, i.e., the anti-misshot device becomes ineffective. Thus, with patients who don't co-operate in adjusting their respiration, an operator can shorten the treament time by lowering the threshold even when ETM is chosen. Therefore, in order to demonstrate the usefulness of the computer-drawn-sketch objectively, farther investigation would be neccesary in which the frequency of shots per second is determined and the threshold of ETM is held sufficiently high.

References

1)Taguchi,K.,Orikasa,S.,Kuwahara,M.,et al.:Initial experience using a new type of extracorporeal lithotriptor with an anti-misshot control device.Jpn.J.Urol.,82:1105-1110,1991.
2)Ajima,J.,Oka,K.,Ozawa,K.,et al:Clinical experience with ESWL monotherapy using a piezoelectric lithotriptor with anti-misshot device(ESL500A).Jpn.J.Endourol.ESWL,6:198-201,1993.

Legends

Fig.1 Ultrasonic monitor image of ESL-500A.
Fig.2 A sketch of renal parenchyma, pelvis, and ureter is drawn on the CRT of a personal computer. The position of a stone (x,y) and its size (L) is input through the keyboard of the computer.
Fig.3 A schema showing a situation as if the shock wave is generated and transmitted to the focal zone.
Fig.4 A schema simulating a situation in which an ureter stone comes in the focal zone when a patient expires.
Fig.5 A schema simulating a situation in which a renal stone comes in the focal zone when a patient inspires.