1100 to 1400 for cancellous bone is generally 900 to 1000 and for bone marrow is generally 200 to 800 the scan data containing radiological density values stored in reconstructor 20 could be used to generate an image which could be displayed in a conventional manner and interpreted by the scan operator or subsequently by doctors the displayed image represents a scan slice of femur 12 such as illustrated in the greatly simplified illustration of fig2 the image is generated by displaying a particular gray level intensity at each x y portion of the crt screen based upon the magnitude of the scan signal corresponding to that x y portion the gray level intensity displayed at each x y crt portion may be simply proportional to the magnitude of scan signal generated for the corresponding x y scan portion the disc memory 18 may be used for temporary storage of scan data from scan memory 16 prior to its being reconstructed by the reconstructor 20 reconstructed data may also be stored in disc memory 18 on a relatively long term basis such as days or weeks for example in connection with the illustrated embodiment of the present invention the reconstructed data is stored in ct scan tape memory 14 which contains the scan slice density data for the complete sequence of scan.