Siemens has completed an investigation of the reported event.Assessment of the dicom imgaes, patient information and qa results does not indicate a system failure or malfunction and no non-conformity was identified.Detailed information regarding the patient´s health status, dicom images of the performed scan, system quality assurance test reports and, information with respect to the metal pieces in the patient´s knee were evaluated.After analysis of the provided dicom images, no indication was found which would indicate a system malfunction.The dicom images are of normal quality.It was determined that the system works as specified and no root cause could be detected which could explain the pain and stiffness of the patient´s left knee.The complete examination of the patient's shoulder lasted 17.8 minutes with an active scanning time of 15.5 min.Which represents a normal examination time.The complete examination (consisting of 7 imaging protocol measurement steps) was performed in the normal operating mode (nm).The sar values were within the limits defined by the mr safety standard (iec 60601-2-33) for the nm.I.E.The maximum applied sar was 72% of the normal mode limit and therefore, the applied sar was totally uncritical.According to the information in the event log, the examination was finalized without the patient pressing the squeeze ball.The applied rf dose in this case should not represent a risk under normal circumstances and scan conditions.Furthermore, the patient absorbed 20.1 wmin / kg which is clearly below the limit of 240 wmin / kg defined in the afore mentioned mr safety standard (iec 60601-2-33).This applied specific (rf) energy dose (sed) is typical for shoulder examinations as performed in this case.No indication was found that a contrast agent was administered for the shoulder examination.In the headers of the mr images there are also entries concerning the stimulation effect of the used protocols.Accordingly, here too - as for sar - the examination was performed in the normal mode (nm, respective stimulation).The intensity of the applied stimulation can be considered moderate.On (b)(6) (roughly half a year after the incident) extensive quality assurance (qa) tests were carried out on site.All results were in accordance with the specification.The save log we received was generated on (b)(6) 2019.The complained issue happened roughly half a year before.Therefore, the save log does not provide any information with respect to the affected scan.The patient complains of severe problems after mri examination in the area of the left knee which had an anterior cruciate ligament (acl) reconstruction surgery ten years ago.During that surgery titanium screws "grade 5" and "grade 23" have been used to fix the cruciate ligament.The reconstruction of the patient positioning showed that the patient´s knees were outside the magnet during the shoulder scan.The slight eccentric position on the table towards the left side (~ 2.5 cm) has no influence on the examination results.The same applies to the receiving coils (shoulder array and spine matrix) used for this examination.The knees were safely outside the effective range of the body coil and the gradient coil.The only potentially remaining influence is the b0 field generated by the system magnet.According to the positioning, the knees were approximately located in the area where ferromagnetic objects experience a particularly strong attraction.However, the used screws (described above) contain a very small amount of iron (proportion 0.4%) and therefore, no significant magnetization occurs.Therefore, when the patient's shoulder was moved into the center of the magnet, the screws in the knee were not exposed to any significant force of attraction.After analyzing the technical data, the reported negative influence on the patient's knee cannot be explained.In addition, the patient stated that there was an abnormal shaking during the mri scan, and he felt an abnormal jolt during the table movement out of the bore.During measurements the gradients always generate vibrations; also, during table movements, it is possible to feel a weak shake but, in this case, the gradients operated rather moderately.In general, the system vibrations as well the table shaking's do not negatively impact the patient.However, very sensitive persons may find this unpleasant.For such unpleasant situations, the system is equipped with a squeeze ball for the patient to alert the operator in the event of experiencing discomfort.With these existing safety features, a death or serious injury is unlikely if this issue reoccurs.The patient speculates that the ligaments have shrunk due to heating causing the stiffening.According to our knowledge, a significant warming of the implanted screws resulting in damage of the implanted ligament has not yet been reported and can therefore be assumed as not possible due to different reasons: the knee was positioned outside the magnet and therefore outside of the effective range of the body coil and as well of the gradient coil.The only potentially remaining influence is the b0 field generated by the system magnet.The measurable sar and db/dt values tend towards zero.The used screws in the affected knee are too short to cause a resonant energy coupling.The effect of gradient fields is determined by induction.Even with metallic conductors, the induction surface must exceed a certain size.The screws represent only a very small induction surface.The heating - even within the magnet at the location of the largest field lift - should be negligible.Even under worst-case conditions, the titanium-alloys only experienced a temperature increase of 1 °c.As already mentioned above, screws represent only a very small induction surface.In addition, a shrinkage of the transplanted ligaments themselves can also be excluded.Indeed, there are rare exotic materials that can contract in case of warming under certain circumstances.But in this case, natural tendons derived from hamstring muscles have been transplanted.In general, every patient has to be asked about implants before an mri examination take place.The operator manual (m6-02001g.621.07.01.02, vd13a) clearly states that an mr examination is contraindicated for patients with implants (see chapter a.2-9).The operator, if nevertheless doing so, always has to evaluate the risk-benefit ratio for every patient.If implants, however, are known to be mr-unsafe, the patient is not allowed to enter the mr examination room at all.The screws do not experience any notable attraction force when moving the patient inside the magnet.This is valid even for 7 t mr systems.The examination has been performed with the avanto dot system that operates with a 1.5 t magnet.Until now, no adverse effects like this have been observed when patients are being moved into the magnet.There is no indication of any malfunction of the system.No further actions are planned by the manufacturer as no system malfunction was identified.
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