Quality Control Program Of Real Time Medical Ultrasound Machines In Sudan

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1 Quality Control Program Of Real Time Medical Ultrasound Machines In Sudan Mamdouh Y Osman a*, Fathi A Taha b a sudan Atomic Energy commission, P.O.Box 3001, Khartoum, Sudan. b Department of Applied Physics, Faculty of Applied sciences, Red Sea University, P.O.Box, 24 Port Sudan, Sudan. Abstract. The quality control program has been applied to 22 of real time ultrasound machines sited at government and private ultrasound diagnostic centres in Khartoum state; the capital of Sudan. The following ten quality control tests were applied to the ultrasound machines; maximum depth of penetration, vertical distance accuracy, horizontal distance accuracy, axial resolution, lateral resolution, image uniformity, dead zone, grey scale, cyst imaging and image recorder. This study is the first of its kind to be performed in Sudan. As there is no internationally agreed upon protocol that shows the accepted level for the quality control tests; two references were selected to evaluate the performance of the tested ultrasound machines; these are published by the American Association of Physicists in Medicine and by the Royal College of Radiologists. Only 22.7 of the tested machines showed the recommended level of performance for all quality control tests. This poor result is mainly due to the fact that so far, there is no regulatory body exist in the country to control the use of non ionizing radiation including ultrasound waves. As a result of that most of the imported ultrasound machines are second hand and they are not subjected to any acceptance test before being set into operation. Also, no regular quality control tests are performed on those machines and this in turn is due to the lack of quality control tools. A new nuclear energy act has been drafted by the radiation protection technical committee of the Sudan atomic energy commission, which is the regulatory body for ionizing radiation. The new act is to establish a new regulatory body to control the use of all types of radiation within the country. KEYWORDS: quality control; ultrasound; nuclear energy act. 1. Introduction According to the Sudan Atomic Energy Commission (SAEC) of 1996, the use of all types of radiation is done under the control of the commission. However, this law has been effectively applied only for ionizing radiation as the commission failed to issue the necessary regulations for controlling the use of non ionizing radiation. Medical ultrasound machines are extensively used in the country mainly for diagnostic purposes. It was until the year 03 when two main hospitals namely radiation and isotopes centre (RICK) and Al Rabat hospital managed to purchase the first quality control (Q.C) tools for ultrasound machines. The aim of this study is to assess the performance of ultrasound machines through performing quality control tests on some of those machines both at governmental and private sector. In addition to that, this study aims to illustrate the necessity of applying quality control program in ultrasound departments. 2. Materials and Methods This study covered 22 ultrasound machines in public and private clinic in Khartoum state. Direct quality control measurements have been applied on such machines using the 403 GS RMI ultrasound phantom shown in figure 1 with its specifications listed in table 1. The targets configuration of the phantom is also shown in figure 2. * Presenting author, mamdouhyas@hotmail.com 1

2 Fig. 1: the 403 GS RMI Table 1: specification of the 403 GS RMI ultrasound phantom Weight Dimensions Scanning surface Case material Pin target material Tissue mimicking material Speed of sound Attenuation coefficient Low scatter (Anechoic) Targets Grey scale targets Pin targets Axial resolution targets group approx 2.8 Kg (23.2 x 8.25 x 18.5) cm composite film extruded ABS plastic. Nylon monofilament. Water based gel with appearance of human tissue. 1540± 10 m/s. 0.5 db /cm/mhz Diameter.. 2, 4, and 6 mm. Placement. 3, 6, 8 and 14 cm deep. Speed of sound ± 10 m/s. Attenuation coefficient.0.05 ± 0.01dB /cm/mhz. Diameter. 10 mm. Placement 6 cm deep. Speed of sound 1540 ± 10 m/s. Temperature dependence on speed of sound..1.5 m /s/c. Contrast.-6dB, +6dB, high scatter (+12dB or +15dB). Diameter.0.1mm. Vertical spacing..2 cm at 2 and 16 cm deep. Horizontal spacing..3cm at 2 and 12 cm deep. Placement.at 3, 8, and 14 cm deep. 2

3 Fig. 2: Targets configuration of 403 GS RMI Ultrasound Phantom For each of the 22 ultrasound machines the following 10 Q.C tests were performed: depth of penetration, vertical & horizontal distance accuracy lateral & axial resolution, image uniformity, dead zone, cyst imaging, grey scale and image recorder test. To assess the situation of the ultrasound machines with respect to their performance and problems that are associated with their use, a questionnaire has been prepared and distributed among the specialists in some of the imaging department e.g. sonographers, physicists and engineers. The stated answers had been then investigated and analysed. 3. Results and Discussion Table 2 shows the technical data of the tested ultrasound machines. The acceptance criteria used in this study were based on two references namely; the report of the American association of Physicist in Medicine (AAPM) [13] and the publication of the royal college of Radiologists standards for ultrasound [14]. However the acceptance criteria for only six tests were stated in these two mentioned references. For the remaining tests namely image uniformity, cyst imaging, grey scale and image recorder, the acceptance criteria were based on what is stated by the phantom manufacturer. Figure 3 sows the overall results of the applied Q.C tests. 3

4 Table 2: technical data of the tested ultrasound machines Machine No Type Transducer Serial Number Frequency MHz Gain db 1 FUKUDA DENSHI FUT C111A GE SIEMENS PD SIEMENS G50 C FUKUDA DENSHI FUT CS 602 5AJ FUKUDA DENSHI FUT-CS 602-5AJ SHIMASONIC MS-SDL Not displayed 7 ALOKA Not displayed FUKUDA DENSHI FUT C ALOKA ECHO CAMERA SH ECCOCEE-TOSHIBA PVF- 375 AT 3.75 Not displayed 11 SIMENS SONOLINE G C SIMENS SONOLINE G60 C TOSHIBA PVM 3.75 AT MEDISON SA600 CONVEX 35/ TOSHIBA PVG 366 M ALOKA-SCC390 SH KONTRON MEDICAL V FUKUDA DENSHI FUT C SONOACER 1500 PC 15 H ALOKA Not displayed FUKUDA DENSHI FUT -C AQUASAFE Not displayed Fig. 3: Overall Results of the Q.C Tests Number (and Percentage) of Ultrasound Machnines Showed the Recommended Performance depth of penetration vertical distance accuracy horizontal distance accuracy lateral resolution axial resolution dead zone image uniformity cyst imaging gray scale image recorder Qulaity Control Test number percentage 4

5 It can be seen from figure 3, about 63.6% of the tested machines showed the recommended depth of penetration. The maximum depth of penetration is limited by the frequency of the transducer and the output power and electrical noise of the system electronics. The maximum depth of penetration should remain constant over time, variations indicate performance degradation. Changes in the depth of penetration are caused by damage to the transducer or cable or malfunctions in the systems transmit and receive circuits. The use of the appropriate transducer for each application would ensure good visualization at sufficient depth of image without significant loss of accurate spatial resolution. [5] Only 40.9% of the tested machines were found to be working within accepted level of horizontal distance accuracy i.e. the accuracy of distances measured perpendicular to the beam axis. Horizontal distance errors can be the result of flaws in the transducer geometry either in the design or through damage. On the other hand the majority of the tested machines passed the vertical distance accuracy test. Vertical distance measurement errors are not always obvious and can easily go unnoticed. This test determines the accuracy of distance measured along the beam axis. Vertical distance errors can be caused by drift or failure in the system internal timing circuits. [13] With respect to resolution tests, all of the tested machines showed the recommended axial resolution while more than 50% of them failed the test of lateral resolution. Lateral resolution is typically affected by the loss of transducer elements or by problems in the systems beam forming circuits [5]. It is worth noted that axial resolution test was not possible to perform on ultrasound waves generated from 31.8% of the tested machines due to their short depth of penetration. The resolution of the ultrasound machine (axial and lateral) is vital for detecting small structures (0.25 mm 2mm). Ultrasound equipment must be capable of visualizing tissue structures in most patients of different body habitus to a diagnostic level sufficient to meet clinical need. [14] A high percentage (90.9%) of the tested ultrasound machines passed the dead zone test which has a recommended value of 5mm. Although many of today's instruments are normally free from noticeable dead zones, damage to the transducer or poor acoustic coupling may produce this defect. Also, the majority of the tested machines (90.9%) showed uniform image (test of image uniformity). However one of the tested machines showed serious artefact on the screen, and another one showed large amount of vertical banding. Vertical banding or shadowing is an indication of a malfunction of a particular transducer element or its associated circuitry. [5] All the tested ultrasound machines showed the required shape, edge and texture for the 6mm cyst in the near field. On the other hand and for the same test but in the far field 68.2% of the tested machines were found not able to display the 6mm cyst. Ultrasound machines should be able to display normal and abnormal tissue details, with the ability to differentiate solid and cystic abnormalities. Cyst image quality can be affected by electrical noise, side lobes in the transducer beam and problems with the image processing hardware. [13] The grey scale tests were performed only on machines equipped with printers and 83.3% of those machines displayed the desired appearance of the grey scale targets, while the rest were not able to discriminate between the contrast of the third and fourth grey scale target. Any defect in the grey scale of ultrasound machine can lead to wrong diagnostic of the patient, because in this case the ultrasound system cannot discriminate between solid and cystic structures. The test of image recorder was performed only on twelve ultrasound machines that have printing devices. The results of image recorder test for all tested machines showed identical information between the image on the screen and image obtained using printer. The most frequently reported source of performance instability of an ultrasound system is related to the recording of the image on film or the display on maladjusted video monitors. Drift of the ultrasound instrument setting or film camera settings, poor film processing conditions, and/or poor viewing conditions can lead to suboptimal image on both hard copy (film) and soft copy (monitor). Some tested ultrasound machines have a facility to store the image of the patient on a memory, and soft copy of the images can be obtained, but most of the users of those machines don t use this facility. This facility could be useful in 5

6 case of ultrasound images of a patient get lost. Also such facility allows images to be shared in a medical information network at any hospital to provide enough historical information related to the patient.[4] Results of the survey that covered 14 government hospitals that have 39 ultrasound machines and 17 private hospitals and clinics with 22 ultrasound machines, showed that the quality control tests for ultrasound machines are performed regularly in only 14.3 % of the governmental hospitals i.e. only in two hospitals and it is not performed at all in the private hospitals and clinics. The main reason behind that is the unavailability of the required test tools. Quality control tests are usually performed by engineers i.e. the engineers have to take the responsibility of carrying out the quality control tests as well as maintenance and repair services, this is always not recommended as quality control tests should be done by a medical physicist or a quality control technician. Most of the surveyed radiologists and sonographers think that there is no need for ultrasound quality control as they believe that most of the newly developed ultrasound machines are very reliable and rarely suffer from any faults. Also they believe that they can detect any defects in image quality during normal scanning. Although both of these statements may be true, they don t necessarily negate the utility of performing ultrasound quality control tests. A prime reason is that a set of periodic definitive measurements for ultrasound machine can identify degradation in image quality well before it affects a patient scans. Another is that when equipment malfunction is suspected; quality control tests can be employed to determine the source of the malfunction. [13] The survey also showed that there are 15.4 % of the total number of ultrasound machines in the governmental hospitals and 22.7 % in the private hospitals and clinics that are out of service or damaged i.e. about 18% of all machines are out of service. The surveyed sonologists, engineers, technicians and medical physicists referred the main reasons that lead to ultrasound machine breakdown to the absence of preventive maintenance. Other reasons like instability of the general electric power supply are also mentioned. In addition to that, the environment of the ultrasound machine e.g. ventilation and room temperature - also plays an important role in causing machine breakdown. In this context the survey showed also that there are some difficulties in securing a qualified service engineer to maintain or repair an ultrasound machine as most of them are quite old and in many cases there is a lack of operation and service manuals. The survey also revealed that quality assurance committees are available in only 7.4 % of the governmental hospitals and in 5.9 % of the private hospitals and clinics. But the quality assurance program in private hospitals and clinics does not include the supervision of a quality control program for ultrasound machines. 4. Conclusion From this first study on the quality control and status of ultrasound machines in Sudan we can conclude that, the absence of preventive maintenance, regularly performed quality control tests and authorized body for regulating the medical use of ultrasound in Sudan are the main reasons behind the degradation of the performance of ultrasound machines where only 22.7% of the tested ultrasound machines in both governmental and private sectors showed the recommended performance for the all the performed quality control tests. The lake of training in maintaining ultrasound equipments lead to the noticeable shortage in the number of expert engineers for maintaining ultrasound equipment. The issue of quality control for medical equipment is in general neglected by the ministry of health which can be considered as a main reason behind the lack of quality control culture among most of the sonographers in the country.this work is to be extended to cover more ultrasound machines both in Khartoum and other states and to include Doppler ultrasound machines. The promulgation of the new nuclear energy act that deals with regulating the use of both ionizing and non-ionizing radiation is expected to enhance the situation as far as the medical use of ultrasonography in the country. 6

7 Acknowledgements The authors wish to thank the hospitals that participated in this study and their staff for their sincere cooperation. REFERENCES [1] Stewart C. Bushong, Radiologic Science for Technologists, 5th edition, Mosby-Year Book, Inc., [2] Perry sprawls, jr., Physical Principles of Medical Imaging, 2nd edition, 1993 [3] James A.Zagzebski, Essentials of ultrasound physics, Don Ladig, [4] Jeffry Papp, Quality management in imaging sciences, Don Ladig, [5] The Q.A Cook book for ultrasound (GAMMEX Company). [6] User manual of 403 GS RMI ultrasound phantom (GAMMEX Company). [7] Jerrold T. Bushberg et al, The Essential Physics of Medical Imaging, Williams & Wilkins, [8] Kremakau FW, Diagnostic Ultrasound: Principles and Instruments, 4th edition, WB Saunders, [9] Andrea Trigg Stevens, Quality Management for Radiographic Imaging, McGraw-Hill, 01. [10] MC Knight RN, Amixing Scheme to focus a transducer array dynamically. Hawlett Packard Journal, P16, December [11] Kendall CJ, Opthalmic echography, Thorofare, NJ, 1990, Slack. [12] Hagen-Ansert L, Textbook for diagnostic ultrasounography, 4th edition, ST.Louis, 1995, Mosby. [13] Mitchell M.Goodsitt and Paul L.Carson, Real-time B-mode Ultrasound Quality Control Test Procedures, Report of Ultrasound Task Group No. 1, Medical Physics, Vol.25, No.8, Augst1998. [14] Royal College of Radiologists, Standards for Ultrasound Equipments, Board of the Faculty of Clinical Radiology- Royal College of Radiologists, RCR Ref NO BFCR (05)1, 05. 7