MAGNETIC-RESONANCE-IMAGING OF URINARY CALCULI

Accurate prediction of the response of an individual patient to lithot ripsy remains impossible. Certain factors such as the chemical composi tion, size, and position of the calculus are known to be important in determining the success rate. This paper reports the use of magnetic r esonance imaging (MRI) to evaluate 141 urinary calculi in vitro. A wid e range of signals for each chemical type of calculus was found on eac h of the three imaging sequences used (T1-weighted, T2-weighted, and p roton density). None of the chemical groups examined showed a typical MRI profile allowing it to be distinguished from the other groups. Ana lysis of variance showed a statistical difference between signals for apatite and struvite on the T1-weighted sequence, and between struvite and uric acid on the proton density sequence (both, P<0.05). These re sults show for the first time that MRI is capable of distinguishing be tween different chemical types of stones. This is particularly importa nt for the comparison of struvite and apatite which appear to be simil ar in conventional investigations but have quite different hardness va lues. Further work is in progress correlating the results of this stud y with stone microhardness and extracorporeal shockwave lithotripsy fr agility tests to determine whether MRI accurately predicts the success of lithotripsy.