SU741486A1

SU741486A1 - X-pay photo exposure meter

Info

Publication number: SU741486A1
Application number: SU782690244A
Authority: SU
Inventors: Владимир Юрьевич Хлебцевич; Лев Владимирович Владимиров; Илья Миронович Моргенштерн
Original assignee: Предприятие П/Я Р-6303
Priority date: 1978-11-29
Filing date: 1978-11-29
Publication date: 1980-06-15

Description

Изобретение относится к технике медицинской рентгенографии и предназначено для ограничения экспозиции при исследовании малоконтрастных объектов.The invention relates to techniques for medical radiography and is intended to limit exposure in the study of low-contrast objects.

Известно устройство для измерения интенсивности излучения за определенный промежуток времени, содержащее фотоэлемент, инвертор, интегратор, выполненные на операционных усилителях, и пороговое устройство.A device for measuring the intensity of radiation for a certain period of time, containing a photocell, inverter, integrator, made on operational amplifiers, and a threshold device.

К недостаткам устройства относятся , значительная погрешность интегрирования фототока, обусловленная дрейфом интегрирующего усилителя, а также необходимость настройки фотоэкспонометра.The disadvantages of the device include a significant error in the integration of the photocurrent due to the drift of the integrating amplifier, as well as the need to adjust the photo exposure meter.

Наиболее близким по технической сущности ₎₅к предложенному является экспонометр рентгенодиагностического аппарата Senographe FX содержащий интегрирующий конденсатор, включенный последовательно с фотоэлектронным умножителем (ФЭУ); коммутирующее и ηοροτοвое устройства.The closest in technical essence _{) 5} to the proposed one is an exposure meter of the Senographe FX X-ray diagnostic apparatus containing an integrating capacitor connected in series with a photoelectronic multiplier (PMT); switching and ηοροτου device.

В этом устройстве относительная чувствительность ФЭУ существенно зависит от напряжения на интегрирующем конденсаторе. По мере накопления заряда на интегрирующем конденсаторе, установленном на выходе ФЭУ, уменьшается напряжение между анодом и последним динодом. Это приводит к значительным ошибкам .экспонирования,-так как коэффициент усиления ФЭУ сильно зависит от величины напряжения, приложенного к его электродам.In this device, the relative sensitivity of the PMT is substantially dependent on the voltage across the integrating capacitor. As the charge accumulates on the integrating capacitor installed at the output of the PMT, the voltage between the anode and the last dynode decreases. This leads to significant errors of exposure, since the gain of the PMT strongly depends on the magnitude of the voltage applied to its electrodes.

Для уменьшения ошибок экспонирования, обусловленных упомянутыми причинами, необходимо, чтобы величина напряжения на интегрирующем конденсаторе была на два порядка меньше напряжения между анодом и последним динодом. Так, например, для ФЭУ-68: при напряжении между анодом и последним динодом 50 В, напряжение на конденсаторе не должно превышать 0,5 В, что соизмеримо с дрейфом полевого транзистора, который ограничивает снизу величину напряжения на интегрирующем конденсаторе.To reduce exposure errors due to the mentioned reasons, it is necessary that the voltage across the integrating capacitor be two orders of magnitude lower than the voltage between the anode and the last dynode. So, for example, for a PMT-68: when the voltage between the anode and the last dynode is 50 V, the voltage on the capacitor should not exceed 0.5 V, which is comparable with the drift of the field-effect transistor, which limits the voltage on the integrating capacitor from below.

Цель, изобретения — повышение точности интегрирования и исключение зависимости фототока от напряжения на интегрирующем конденсаторе.The purpose of the invention is to increase the accuracy of integration and the exclusion of the dependence of the photocurrent on the voltage at the integrating capacitor.

741486 ' 4741486 '4

Поставленная цель достигается тем, что в рентгеновский фотоэкспонометр, содержащий интегрирующий конденсатор, подключенный последовательно к фотоэлектронному умножителю с резистивным делителем напряжения пита· ния динодов, катод которого соединен с отрицательным зажимом источника питания, коммутирующее и пороговое устройство, согласно изобретению, введен истоковый повторитель напряжения с источником тока, причем выход истокового повторителя соединен с положительными зажимами источника питания и резистивного делителя напряжения, его вход подключен к аноду ФЭУ и интегрирующему конденсатору, а между входом и выходом истокового повторителя включен резистор.This goal is achieved by the fact that in the x-ray photoelectricmeter containing an integrating capacitor connected in series to a photoelectronic multiplier with a resistive voltage divider · dynode power supply, the cathode of which is connected to the negative terminal of the power source, a switching and threshold device, according to the invention, a source voltage follower with a current source, and the output of the source follower is connected to the positive terminals of the power source and the resistive voltage divider, its input is connected to the PMT anode and the integrating capacitor, and a resistor is connected between the input and output of the source follower.

На чертеже представлена структурная схема предложенного рентгеновского фотоэкспонометра.The drawing shows a structural diagram of the proposed x-ray photo exposure meter.

Фотоэкспонометр содержит преобразователь 1 рентгеновского излучения в сзетовое излучение; источник питания 2; ФЭУ 3 с резистивным делителем напряжения питания диодов, интегрирующий конденсатор 4, коммутирующее устройство 5, резистор 6, истоковой повторитель 7 напряжения, источник тока 8, пороговое устройство 9.The photo-exposure meter comprises a converter 1 of x-ray radiation into a cetacean radiation; power supply 2; PMT 3 with a resistive divider of the supply voltage of the diodes, an integrating capacitor 4, a switching device 5, a resistor 6, a source voltage follower 7, a current source 8, a threshold device 9.

Устройство работает следующим образом.The device operates as follows.

Рентгеновское излучение в преобразователе 1, например сцинтилляторе Cs (Ή), преобразуется в световое, которое возбуждает фототок в ФЭУ 3, заряжающий интегрирующий конденсатор 4. Напряжение на конденсаторе 4 повторяется на выходе истокового повторителя 7, Постоянство напряжения смещения ’’входвыход” истокового повторителя Ί обеспечивается с помощью источника тока 8 и используется для компенсации темнового тока ФЭУ с помощью резистора 6. Так как положительные зажимы источника питания 2 и резистивного делителя напряжения питания динодов; ФЭУ 3 подключены к выходу истокового повторителя 7, напряжения на катоде и динодах относительно анода ФЭУ остаются постоянными. При достижении на интегрирующем конденсаторе напряжения срабатывания, соответствующего заданному значению экспозиции, на выходе порогового устройства 9 появляется сигнал на отключение рентгенодиагностического аппарата. После окончания экспозиции происходит разряд интегриру ющего конденсатора 4 с помощью коммутирующего устройства 5.X-ray radiation in the transducer 1, for example, the scintillator Cs (Ή), is converted into light, which excites the photocurrent in the PMT 3, charging the integrating capacitor 4. The voltage on the capacitor 4 is repeated at the output of the source follower 7, The bias voltage is constant, the “input-output” of the source follower Ί is provided by a current source 8 and is used to compensate for the dark current of a PMT with a resistor 6. Since the positive terminals of power supply 2 and the resistive divider of the power supply dynodes; PMT 3 are connected to the output of the source follower 7, the voltage at the cathode and dynodes relative to the PMT anode remain constant. When the operating voltage on the integrating capacitor reaches the set exposure value, a signal to turn off the X-ray diagnostic device appears at the output of the threshold device 9. After the exposure is complete, the integrating capacitor 4 is discharged using the switching device 5.

Источник питания 2 ФЭУ выполнен в виде преобразователя постоянного стабилизирован5 ного напряжения в переменное, на выходе которого включен повышающий трансформатор с выпрямителем, причем вторичная цепь трансформатора не заземлена.The power source 2 of the PMT is made in the form of a converter of constant stabilized voltage to alternating voltage, the output of which includes a step-up transformer with a rectifier, and the secondary circuit of the transformer is not grounded.

Существенным преимуществом предложен10 ного рентгеновского фотоэкспонометра является высокая точность интегрирования, обеспечиваемая простыми техническими средствами. Фототок практически не зависит от напряжения на интегрирующем конденсаторе. Это позволя15 ет использовать все возможности истокового повторителя напряжения, в качестве которого применяют, например, полевой транзистор КП302А, и довести напряжение на интегрирующем конденсаторе до 20 В (дрейфом полевого 20 транзистора можно пренебречь). Коэффициент нелинейности заряда конденсатора при этом составляет не более 10^_3.A significant advantage of the proposed X-ray photo-exposure meter is the high accuracy of integration provided by simple technical means. The photocurrent is practically independent of the voltage across the integrating capacitor. This makes it possible to use all the possibilities of the source voltage follower, for example, the KP302A field-effect transistor, and bring the voltage on the integrating capacitor to 20 V (drift of the field-effect transistor 20 can be neglected). The nonlinearity coefficient of the capacitor charge in this case is not more than 10 ^_3 .

Предложенное устройство обеспечивает также высокую точность измерения интенсивности из25 лучения при замене интегрирующего конденсатора активным сопротивлением, что важно, например, для целей компьютерной томографии.The proposed device also provides high accuracy in measuring the radiation intensity when replacing the integrating capacitor with active resistance, which is important, for example, for computed tomography.

Claims

The invention relates to a medical X-ray technique and is intended to limit exposure in the study of small areas of plant objects. A device for measuring the intensity of radiation for a certain period of time is known, which contains a photocell, an inverter integrator, made on the operating points, and a threshold device. The disadvantages of the device include a significant error in the integration of the photocurrent caused by the drift of the integrating amplifier, as well as the need to adjust the photoexponometer. The closest in technical essence to the proposed is the exposure meter of the Senographe FX single-sensor apparatus containing an integrating capacitor connected in series with a photomultiplier tube (PMT); Commuting and noporo devices. In this device, the relative sensitivity of a PMT substantially depends on the voltage across the integrating capacitor. As the charge builds up on the integrating capacitor installed at the output of the PMT, the voltage between the anode and the last dynode decreases. This leads to significant faults, because the gain of the photomultiplier is strongly dependent on the magnitude of the voltage applied to its electrodes. In order to reduce the exposure error caused by the aforementioned reasons, it is necessary that the voltage on the integrating capacitor be two orders of magnitude smaller than the voltage between the anode and the last dynode. Thus, for example, for PMT-681, when the voltage between the anode and the last dynode is 50 V, the voltage across the capacitor should not exceed 0.5 V, which is commensurate with the drift of the field-effect transistor, which limits the voltage across the integrating capacitor from below. The goal of the invention is to improve the integration accuracy and eliminate the dependence of the photocurrent on the voltage across the integrating capacitor. This goal is achieved by the fact that an X-ray photoelectron meter containing an integrating capacitor connected in series to a photomultiplier with a resistive voltage divider or dynodes, the cathode of which is connected to the negative power supply terminal, the switching and threshold device according to the invention, has a source follower current source, the output of the source follower is connected to the positive terminals of the power source and resistive voltage divider its input is connected to the anode of the photomultiplier and the integrating capacitor, and a resistor is connected between the input and output of the source follower. The drawing shows a structural diagram of the proposed X-ray photoelectron meter. The photoexposure meter contains an X-ray to light radiation converter 1; power source 2; A PMT 3 with a resistive divider supply voltage divider, an integrating capacitor 4, a switching device 5, a resistor 6, a voltage source follower 7, a current source 8, a threshold device 9. The device operates in the following way. Reshtenov radiation in converter 1, for example, Cs (T) scintillator, is converted into light, which excites a photocurrent in a photomultiplier 3, charging the integrating capacitor 4. The voltage on the capacitor 4 is repeated at the output of the source follower 7, Bias voltage condition the input of the output of the source follower 7 is provided by a current source 8 and is used to compensate for the dark current of the PMT with a resistor 6. Since the positive terminals of the power source 2 and the resistive divider are the power supply of the dynodes; The PMT 3 is connected to the output of the source follower 7, the voltages on the cathode and on the diodes relative to the anode of the PMT remain constant. When on the integrating capacitor, the response voltage corresponding to the specified exposure value reaches the output of the threshold device 9 and a signal appears to turn off the X-ray diagnostic apparatus. After the 4aifflH exposure, the integrating capacitor 4 is discharged by the switching device 5. The power source 2 of the PMT is implemented as a constant stabilized voltage to AC converter, the output of which includes a step-up transformer with a rectifier, and the secondary circuit of the transformer is not grounded. A significant advantage of the proposed X-ray photoelectron meter is the high accuracy of integration provided by simple technical means. The photocurrent is almost independent of the voltage across the integrating capacitor. This makes it possible to use all the capabilities of the source voltage follower, for example, the KP302A field-effect transistor, and bring the voltage across the integrating capacitor to 20 V (the drift of the field-effect transistor can be neglected). The coefficient of nonlinearity of the charge of the capacitor in this case is no more than 10. The proposed device also provides high accuracy of measuring the intensity of radiation when replacing the integrating capacitor with active resistance, which is important, for example, for the purposes of computed tomography. Claims of the invention X-ray photoelectron meter comprising an integrating capacitor connected in series to a photomultiplier with a resistive voltage divider, power supply of dynodes, the cathode of which is connected to the negative terminal of the power source, switching and threshold devices, different in that, in order to improve the accuracy of integration and elimination of the power supply, a switching device and a threshold device, characterized in that, in order to improve the accuracy of the integration and elimination of the power supply, a switching device and a threshold device, characterized in that, in order to improve the accuracy of the integration and elimination of the power supply, a switching device and a threshold device, characterized in that, in order to improve the accuracy of the integration and elimination of the power supply, a switching device and a threshold device, characterized in that, in order to improve the accuracy of the integration and elimination of the power supply, a switching device and a threshold device are different in that in order to improve the accuracy of integration and elimination of the power supply. from the voltage on the integrating capacitor, a source voltage follower with a current source is inserted into it, and the output is The wire follower is connected to the positive terminals of the power supply and resistive voltage divider, its input is connected to the anode of the photoelectric multiplier and the integrating capacitor, and a resistor is connected between the input and output of the source follower.