Abstract:
The invention relates to a medical diagnostic X-ray apparatus ( 1 ) comprising an X-ray source ( 13 ), a hollow carrier ( 5 ) to which the X-ray source is connected, and a cooling mechanism ( 3 ) provided with a cooling means to cool the X-ray source ( 13 ) during use of the X-ray apparatus ( 1 ). The cooling construction ( 3 ) extends completely inside the hollow carrier ( 5 ) thus reducing the risk of leakage of cooling means.

Description:
FIELD OF THE INVENTION 
     The invention relates to a medical diagnostic X-ray apparatus comprising: 
     an X-ray source, 
     a hollow carrier to which said X-ray source is connected, 
     and a cooling device containing a cooling agent for cooling the X-ray source during operation of the X-ray apparatus. 
     BACKGROUND OF THE INVENTION 
     A medical diagnostic X-ray apparatus of the type mentioned in the opening paragraph is known from German Utility Model DE 295 10 802 U1. The known X-ray apparatus is an X-ray apparatus which is suitable for surgical applications. This X-ray apparatus is provided with a C-arc as a hollow carrier to which the X-ray source is connected, and has a cooling device comprising a double-walled envelope of the X-ray source. A cooling agent flows through the double-walled envelope of the X-ray source, said cooling agent being supplied through cooling agent conduits and being discharged by a cooling unit located outside the C-arc. The cooling unit, the cooling agent, the cooling agent conduits and the double-walled envelope of the X-ray source form part of the cooling device of the known X-ray apparatus. 
     During operation of an X-ray apparatus, the production of X-rays by the X-ray source causes the generation of much heat. If this heat is not dissipated, the temperature of the X-ray source increases and eventually also the temperature of the rest of the X-ray apparatus increases. If the temperature of the X-ray source exceeds a certain threshold value, the X-ray apparatus is automatically switched off for safety reasons and the temperature of the X-ray source first has to decrease to a value below said threshold value before the X-ray apparatus can be switched on again. In order to ensure that, in comparison with X-ray apparatus without a cooling device, a longer, uninterrupted time of operation of an X-ray apparatus is possible, the known X-ray apparatus is provided with a cooling device. 
     For surgical applications very strict rules apply as regards the hygiene in treatment rooms, so that patients with open wounds cannot be infected by pathogens and the like. The use of X-ray apparatus with a cooling device causing air or another cooling agent to be blown into the treatment room is therefore not allowed. In the known X-ray apparatus which is suitable for surgical applications, the X-ray source is cooled by means of a cooling device having a double-walled envelope of the X-ray source through which a cooling agent flows. A cooling unit located outside the C-arc ensures that the cooling agent is first passed through a first cooling agent conduit, which extends partly via the inside of the C-arc, and then supplied to the double-walled envelope of the X-ray source. There the cooling agent absorbs part of the heat generated by the X-ray source during the production of X-rays and, subsequently, the cooling agent is carried away again to the cooling unit through a second cooling agent conduit which extends partly through the C-arc. 
     In order to be able to correctly position the X-ray source with respect to a patient, without the position of the X-ray source varying during operation of the X-ray apparatus, the C-arc is accurately balanced. A mass-change of the C-arc can disturb this delicate balance. In order to keep the disturbance of the balance of the C-arc to a minimum, as compared to an X-ray apparatus without a cooling device, the mass increase of the C-arc is kept as small as possible in the case of the known X-ray apparatus. To achieve this, the cooling unit is placed outside the C-arc and, as compared to an X-ray apparatus without a cooling device, an increase of the mass of the C-arc is caused only by the double-walled envelope of the X-ray source, the cooling agent conduits, insofar as they are situated in the C-arc, and the cooling agent present in the cooling agent conduits in the C-arc. 
     A drawback of the known X-ray apparatus suitable for surgical applications and provided with a cooling device having a double-walled envelope of the X-ray source, the cooling unit of which is situated outside the C-arc, resides in that the use of this cooling device involves the risk of leakage of cooling agent. The reason for this being that the connections of the cooling agent conduits to the cooling unit and the double-walled envelope of the X-ray source are a weak point in the construction of the known cooling device, and particularly the connections of the cooling agent conduits to the cooling unit located outside the C-arc can become detached during operation of the X-ray apparatus, causing cooling agent to leak into the treatment room. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a medical diagnostic X-ray apparatus of the type mentioned in the opening paragraph, which is provided with a cooling device having a reduced risk of leakage of cooling agent as compared to the cooling device of the known X-ray apparatus. 
     The object is achieved by a medical diagnostic X-ray apparatus in accordance with the invention, which is characterized in that the cooling device extends entirely within the carrier. The cooling device comprising a cooling agent circulating exclusively within the carrier cools the X-ray source in that the cooling agent absorbs the heat generated during the production of X-rays. Subsequently, this cooling agent transmits the heat absorbed to the carrier which subsequently transmits the heat to the surroundings of the X-ray apparatus. As the cooling device extends exclusively within the hollow carrier, the cooling device in accordance with the invention does not have any connections of the cooling agent conduits which extend outside the carrier and which can become detached during operation of the X-ray apparatus with the associated risk of cooling agent leaking into the treatment room. 
     An additional advantage is that the X-ray apparatus in accordance with the invention does not have cooling agent conduits which extend, at least partly, outside the carrier. After all, this means that during operation of the X-ray apparatus, mechanical stress cannot build up in the cooling agent conduits, which stress adversely affects the balance of the carrier, causing the position of the X-ray source to change with respect to a patient during operation of the X-ray apparatus. In addition, by virtue of the absence of cooling agent conduits extending, at least partly, outside the carrier, the accessibility of the X-ray apparatus is increased for both patients and medical staff. This is of particular importance if the X-ray apparatus is used in a space of limited dimensions, such as a treatment room. 
     A preferred embodiment in accordance with the invention is a medical diagnostic X-ray apparatus, characterized in that the cooling device extends substantially within the entire carrier. By virtue thereof, the heat generated during the production of X-rays and absorbed by the cooling agent can be transmitted to the entire carrier which subsequently transmits the heat to the surroundings of the X-ray apparatus. By virtue of the fact that not only a small part of the carrier, but rather the entire carrier can absorb the heat originating from the X-ray source, and can transmit said heat to the surroundings, the total heat capacity and the total radiation surface of the carrier are used, as a result of which very efficient cooling of the X-ray apparatus is achieved. It is to be noted that, under certain conditions, a securing piece for securing the X-ray source to the carrier, or for securing a detector suitable for detecting X-radiation to the carrier, may form part of the carrier. 
     A further preferred embodiment in accordance with the invention is a medical diagnostic X-ray apparatus, which is characterized in that the cooling agent is in direct thermal contact with the carrier. By bringing the cooling agent in direct thermal contact with the carrier, and by dispensing with the use of cooling agent conduits extending substantially within the entire carrier, the efficiency of the heat transfer between the cooling agent and the carrier is increased and further improved cooling of the X-ray apparatus is achieved. 
     Further improved cooling of the X-ray apparatus is achieved if the carrier is provided with an internal partition which creates at least two channels through which the cooling agent can circulate through the carrier. An example of such an internal partition is a partitioning wall extending in the carrier and parallel to the carrier, which partitioning wall is provided with at least two openings for the circulation of the cooling agent, so that the individual channels are in direct communication with each other. Preferably one of the at least two openings in the partitioning wall is situated in the direct vicinity of the X-ray source at one end of the carrier, and the second opening is preferably situated in the direct vicinity of the other end of the carrier. 
     A still further preferred embodiment in accordance with the invention is a medical diagnostic X-ray apparatus, which is characterized in that the cooling agent is air. 
     An advantage of the use of air as the cooling agent is that air is already present in the hollow carrier and that there is no need for a separate cooling agent. By virtue thereof, the cooling device is not only simpler than a cooling device using a separate cooling agent but also cheaper. 
     Another advantage of the use of air as a cooling agent is that air is a light cooling agent. In order to cause air to circulate through the carrier, there is no need for a heavy expensive pump as would be necessary, for example, in the case of oil or water as a cooling agent; instead the use of a fan is sufficient. By virtue thereof, the cooling device is not only cheaper than a cooling device using a heavy, expensive pump, but, by virtue of the light cooling agent and the fan, it is also substantially lighter than a cooling device making use of a heavier cooling agent and a heavy, expensive pump, and, in addition, the balancing of the carrier is much less adversely affected than in the case of a cooling device using a heavier cooling agent than air and a heavy, expensive pump. 
     An embodiment in accordance with the invention is a medical diagnostic X-ray apparatus, which is characterized in that the cooling device is provided with an envelope, the X-ray source being located within the envelope. The envelope provides a large radiation surface, so that the heat generated during the production of X-rays by the X-ray source situated within the envelope can be transmitted more efficiently, by means of the large radiation surface, to the rest of the cooling device and ultimately to the surroundings of the X-ray apparatus. The envelope may additionally comprise a further cooling agent. Transformer oil would be a practical choice for the further cooling agent, because transformer oil has a very poor electrical conductivity, as a result of which breakdown of the high voltage of the X-ray source is precluded. Of course, within the envelope, other cooling agents can also be used. The envelope within which the X-ray source is located does not only increase the efficiency of the cooling device of the X-ray apparatus, but also has the practical advantage that it keeps the further cooling agent in the direct vicinity of the X-ray source and that, if the X-ray source must be replaced, replacement can include replacement of the envelope, so that the risk of leakage of the further cooling agent comprised in the envelope is minimal. 
     A further embodiment in accordance with the invention is a medical diagnostic X-ray apparatus, which is characterized in that the envelope is provided with cooling ribs. The use of cooling ribs causes the surface of the envelope around the X-ray source to be increased, leading to a further increase of the efficiency of the cooling device of the X-ray apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects of the invention will be further elucidated with reference to the drawings, wherein: 
         FIG. 1  is a diagrammatic side view of an exemplary embodiment of a medical diagnostic X-ray apparatus in accordance with the invention, 
         FIG. 2  is a diagrammatic cross-sectional view taken on the line A-A in  FIG. 1 , 
         FIG. 3   a  is a diagrammatic cross-sectional view taken on the line B-B in  FIG. 1 , 
         FIG. 3   b  is a diagrammatic cross-sectional view taken in the line C-C in  FIG. 1 , and 
         FIG. 4  is a qualitative view of the temperature of the X-ray source as a function of the time during which the X-ray source is in operation, said X-ray source forming part of: 
       a) a medical diagnostic X-ray apparatus without a cooling device, 
       b) a medical diagnostic X-ray apparatus provided with a cooling device in accordance with the invention, without an envelope of the X-ray source, and 
       a medical diagnostic X-ray apparatus provided with a cooling device in accordance with the invention, comprising an envelope of the X-ray source that is provided with cooling ribs, and said envelope containing a further cooling agent. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a diagrammatic side view of an exemplary embodiment of a medical diagnostic X-ray apparatus  1  provided with a cooling device  3  in accordance with the invention. In the exemplary embodiment shown, the X-ray apparatus  1  is provided with a rotatable carrier, i.e. a C-arc  5 , and a frame  7  which guides the C-arc and with respect to which the C-arc  5  can be rotated. The frame  7  is rotatable about a horizontal shaft  9  and is connected, via this shaft  9 , to a stand  11  which is movably located on the floor. At one end of the C-arc  5  there is an X-ray source  13  that is situated within an envelope  15  provided with cooling ribs  17 . An X-radiation detector  19 , in this case an image amplifier, is attached to the other end of the C-arc  5  so as to be diametrically opposite the X-ray source  13 . By rotating the frame  7  about the horizontal shaft  9 , and by rotating the C-arc  5  with respect to the frame  7 , the X-ray source  13  and the X-radiation detector  19  can be positioned relative to a patient, such that the part of the patient to be examined is situated between the X-ray source  13  and the X-radiation detector  19 . The C-arc  5  is provided on the inside with two channels  21  and  23  which are separated from each other by a thin partitioning wall  25 , and through which channels the air present in the C-arc  5  circulates as a cooling agent. The arrows in  FIG. 1  indicate that the direction of circulation of the air through channel  21  is opposite to the direction of circulation of the air through channel  23 . At the end of the C-arc  5  where the X-ray source  13  is situated, a fan  27  is arranged inside the C-arc  5 , which fan brings about the actual circulation of air as a cooling agent through the C-arc  5 . The exact location of the fan  27  is not relevant, therefore it could also be arranged, if necessary, in the direct vicinity of the X-radiation detector  19 . The thin partitioning wall  25  between the channels  21  and  23  has at least two openings  29  and  31  for the circulation of the cooling agent, so that the individual channels  21  and  23  are in direct communication with each other. Opening  29  is in the direct vicinity of the X-ray source  13  at one end of the C-arc  5 , and opening  31  is situated in the direct vicinity of the X-radiation detector  19  at the other end of the C-arc  5 . In addition to the air in the carrier  5  functioning as a cooling agent, the individual channels  21  and  23 , the partitioning wall  25 , the fan  27  and the openings  29  and  31 , also the envelope  15  provided with cooling ribs  17 , within which envelope the X-ray source  13  is arranged and which is provided with a further coolant, form part of the cooling mechanism  3  shown in  FIG. 1 . 
     It is of course possible to use another gas or a liquid as the cooling agent instead of air. However, it has been found in practice that substitution of air with another gas as the cooling agent hardly results in better cooling of the X-ray source  13 . In addition, the use of another gas as the cooling agent is generally more expensive than air, because the other gas, unlike the air already present in the C-arc  5 , first has to be introduced into the C-arc  5 . In addition, the use of a gas other than air entails the risk that, for example in the case of a repair to the C-arc  5 , the gas leaks out of the C-arc  5 , so that the C-arc  5  has to be refilled, at some point in time, with the gas used as the coolant. The use of a liquid as the cooling agent instead of air, however, does lead to better cooling of the X-ray source  13 . In that case, the fan  27  has to be replaced by a pump unit which causes the liquid to circulate through a closed circuit extending entirely in the C-arc  5 . However, by using a liquid instead of air as the cooling agent, the X-ray device  1  becomes much more expensive, because the liquid must first be introduced into the C-arc  5  and a liquid is more expensive than air. Besides, the use of a liquid instead of air as the cooling agent causes the weight of the C-arc  5  to increase substantially, which is detrimental to the balancing of the C-arc  5 . Furthermore, repairs to the C-arc  5  and changing the X-ray source become much more difficult if a liquid is used as the cooling agent instead of air. 
     In practice, the X-ray source  13  is almost always situated in an envelope  15  filled with transformer oil, because this oil has a very poor electrical conductivity, so that breakdown of the high voltage of the X-ray source is precluded. The process of filling oil into the envelope  15  is expensive, so that in the case of wear of the X-ray source  13 , the X-ray source is always replaced together with the envelope  15  filled with the transformer oil. In practice, in the cooling device for cooling the X-ray source, two separate cooling concepts are employed, that is to say, air and transformer oil are used as the cooling agent, so that the X-ray source can be readily replaced without the need to work with oil in a treatment room, such as an operation theater in a hospital. 
       FIG. 2  is a diagrammatic cross-sectional view taken on the line A-A in  FIG. 1  and shows the separate channels  21  and  23  through which air circulates as the cooling agent, and the thin partitioning wall  25  which separates the channels  21  and  23  from each other. In the simplest case, in which the X-ray source  13  is not surrounded by an envelope, air is supplied to the X-ray source  13  via the channel  21  in order to absorb the heat produced by the X-ray source  13  during the production of X-radiation. Via the channel  23 , the air that has absorbed the heat from the X-ray source  13  is removed from the X-ray source  13  and the absorbed heat is transferred to the C-arc  5  before the air is supplied again to the X-ray source  13  via channel  21 . 
     However, in  FIG. 2  the X-ray source  13  is surrounded by an envelope  15  provided with cooling ribs  17 . The envelope  15  is filled with transformer oil which, in addition to air in the C-arc  5 , serves as a further cooling agent for the X-ray apparatus  1 . The transformer oil absorbs the heat generated by the X-ray source  13  during the production of X-radiation. This heat is subsequently transmitted to the air in channel  23  serving as a cooling agent, which air subsequently transmits the heat to the C-arc  5  which, in turn, transfers the heat to the surroundings of the X-ray apparatus  1 . The cooling ribs  17  of the transformer oil-filled envelope  15  of the X-ray source  13  create a larger radiation surface of the envelope, thereby improving the efficiency of the cooling device of the X-ray apparatus. Channel  33 , which, like the channels  21  and  23 , is situated in the C-arc  5 , but through which no cooling agent circulates, engages the frame  7  and its importance lies in the fact that it enables the C-arc  5  to rotate with respect to the frame  7 . 
       FIG. 3   a  is a diagrammatic cross-sectional view of the C-arc  5  taken on the line B-B in  FIG. 1 , in which the separate channels  21  and  23  are shown through which the air functioning as the cooling agent is circulated. The channels  21  and  23  are separated from each other by the thin wall  25 . Channel  33 , through which no cooling agent circulates, engages frame  7  and is important in that it enables the C-arc  5  to be rotated with respect to the frame  7 . 
     For comparison with  FIG. 3   a  showing a diagrammatic cross-sectional view taken on the line B-B in  FIG. 1 ,  FIG. 3   b  diagrammatically shows a cross-sectional view of the C-arc  5  taken on the line C-C in  FIG. 1 . In this Figure, like in  FIG. 3   a , the separate channels  21  and  23 , the thin wall  25  and the channel  33  are shown. However, unlike  FIG. 3   a , the thin wall  25  in  FIG. 3   b  is provided with an opening  31  which allows the channels  21  and  23  to be in direct communication with each other and through which the air can pass from one channel to the other channel. 
       FIG. 4  is a qualitative view of the temperature of the X-ray source as a function of the time during which the X-ray source is in operation, said X-ray source forming part of: 
     a) a medical diagnostic X-ray apparatus without a cooling device, 
     b) a medical diagnostic X-ray apparatus provided with a cooling device in accordance with the invention, without an envelope of the X-ray source, and 
     a medical diagnostic X-ray apparatus provided with a cooling device in accordance with the invention, comprising an envelope of the X-ray source that is provided with cooling ribs, the envelope containing a further cooling agent. 
     In  FIG. 4 , the temperature T of the X-ray source is plotted along the vertical axis. Also the threshold value for the temperature of the X-ray source, T threshold , is plotted along the vertical axis, T threshold  being the temperature above which the X-ray apparatus is automatically switched-off for safety reasons. By setting such a threshold value of the temperature, it is precluded that medical staff or patients can come into contact with hot parts of the X-ray apparatus. In  FIG. 4 , time in random units is plotted along the horizontal axis. The point in time t A  indicates how long it takes before an X-ray source in a medical diagnostic X-ray apparatus without a cooling device has reached the threshold for the temperature. The point in time t B  indicates how long it takes before the threshold value for the temperature of the X-ray source is attained if the X-ray source forms part of a medical diagnostic X-ray apparatus provided with a cooling device in accordance with the invention, but without an envelope of the X-ray source. The qualitative view of  FIG. 4  clearly shows that the time it takes before the threshold value of the temperature of the X-ray source is attained is substantially longer if the X-ray source forms part of an X-ray apparatus provided with a cooling device in accordance with the invention, as compared with the situation in which the X-ray source forms part of an X-ray apparatus which is not provided with a cooling device for cooling the X-ray source. In other words,  FIG. 4  clearly shows that t B  is much larger than t A , which means that the period of time during which a medical diagnostic X-ray apparatus provided with a cooling device in accordance with the invention can be used without interruption before being switched off automatically for safety reasons is much longer than that of a medical diagnostic X-ray apparatus without a cooling device for the X-ray source. 
     If the X-ray source forms part of an X-ray apparatus comprising a cooling device in accordance with the invention including an envelope with cooling ribs enveloping the X-ray source, the envelope containing a further cooling agent, then the improvement of the efficiency of the cooling device is such that the X-ray apparatus can be used without interruption for a period of time t C . In practice it has even been found possible to attain an uninterrupted period of operation of the X-ray apparatus which is twice as long as that of an X-ray apparatus without a cooling device. 
     The invention is particularly suitable for surgical applications, as in this case, due to the strict rules regarding hygiene in treatment rooms, air is not allowed to be blown into the treatment room. Apart from stationary X-ray apparatus, the invention is also relevant for mobile X-ray apparatus for surgical applications. 
     The invention makes it possible for medical staff to perform their duties without any, or with much less, interruptions than before, without there being a risk of leakage of the cooling agent during operation of the X-ray apparatus. The invention also enables interventions to be performed without interruption for a longer period of time than was previously possible. Besides, the invention is very practical, as there is a tendency towards patients gradually getting fatter. The fatter a patient is, the higher the degree of absorption and scattering of X-radiation, and the larger the power of the X-ray source must be in order to be able to produce qualitatively good images of a patient. As the power of the X-ray source increases, more heat is generated during the production of X-radiation by the X-ray source, and the threshold value for the temperature at which the X-ray apparatus is automatically switched off for safety reasons is reached sooner. The invention makes it possible, also in the case of fat patients, to achieve a sufficiently long uninterrupted period of operation of the X-ray apparatus.