The Value of MRI before Prostate Biopsy FIG. 3. (A) A 74-year-old male with prostate cancer. The PSA level was 7.3 ng/ml, GS was 7. The radical prostatectomy speci- men showed one clear cancer foci. (B) The MRI images show a focal, round, low signal intensity area in the left peripheral zone. 　In group 1, the sensitivity for prostate cancer detection was 84.8%, the positive predictive value was 75.7%, and the matching rate of the prostate cancer location was 89.3%. In group 2, the sensitivity for prostate cancer detection was 92.4%, the positive predictive value was 92.4%, and the matching rate of the prostate cancer location was 94.1%. DISCUSSION Recently, PSA screening tests have been widely performed for the early diagnosis of prostate cancer. As a result, for patients with an elevated PSA value, patients who require additional examinations such as TRUS and prostate biop- sy are on the rise. Consequently, early prostate cancer with small lesions and early stage disease is being abundantly detected [18,19]. 　Basically, prostate cancer is diagnosed according to PSA values and the pathologic results of (transrectal ultra- sonography-guided) prostate biopsy. The purpose of pros- tate biopsy is to confirm prostate cancer lesions as well as to assess the location of cancer, lesion size, and grade. The extended 10 to 12 core biopsy that is currently performed at many medical institutions examines the posterior direc- tion of the peripheral zone. It thus has been reported that approximately 30% of cancer lesions located in the anterior peripheral zone, the lateral part, the transition zone, and the midline preurethral anterior fibromuscular stroma may be overlooked [20,21]. In addition, due to the sampling 575 error that may occur during the specimen collection stage, the assessment of the location of cancer lesions has limited sensitivity [5]. Diverse sensitivities of prostate cancer de- tection by transrectal prostate biopsy have been reported, from approximately 50% to 75%. It has been reported that the sensitivity of diagnosis could be raised up to 95% by use of extended 10 to 12 core biopsy [22]. Although prostate bi- opsy shows high accuracy for the detection of cancer le- sions, a small number of patients are still diagnosed as be- ing negative by biopsy [23]. 　In such a case, when a prostate biopsy of a patient with an elevated PSA is negative, urologists face a dilemma [24,25]. Many indexes of prostate cancer applying the PSA value have been reported. Although such indexes show the risk or probability for the presence of prostate cancer, the lesion site cannot be assessed by the application of indexes [26,27]. In addition, it has been suggested that biopsy be performed again on such patients, and to perform biopsy on more sites; nonetheless, such patients experience in- creased cost and an increased morbidity rate [28]. 　MRI differs from other radiological diagnosis methods such as X-ray or computed tomography, because it does not engage ionized radiation and thus is not harmful to the body. The plane images can be reconstructed as 3D images, and contrast and resolution are superior to computed tomography. In addition, images can be constructed at var- ious angles; thus, it is useful for examining intra-pelvic or- gans such as the prostate. According to previous reports, the sensitivity of prostate cancer detection by MRI is ap- proximately 55% to 65%, and the positive predictive value has been reported to be approximately 80% to 85%. Due to the development of advanced technical methods such as diffusion-weighted imaging, dynamic-contrast-enhanced MRI, and MR spectroscopy, the sensitivity is on the rise [5,29,30]. 　In both group 1 and group 2, the sensitivity for detecting prostate cancer was shown to be higher than in other older studies. One reason for this difference may be that PSA and other clinical information of the patients were shared by the radiologists; thus, during the interpretation, the in- formation could be used as reference data. Hence, the possi- bility of bias may be considered. In addition, it is thought that the techniques applying MRI were greatly improved in comparison with the past, and the development of ad- vanced equipment may be of help to raise sensitivity. This could be confirmed by the difference in the sensitivity for detecting prostate cancer between group 1 and group 2. The sensitivity and positive predictive value of group 1 were lower than those of group 2. This may be because in the group 2 cases, images were assessed after the pathologic diagnosis. In group 1, the images were assessed before the pathologic diagnosis. 　Transrectal prostate biopsy is a useful method for diag- nosing prostate cancer and for assessing the location of le- sion, and it has been considered to be the standard assess- ment for detecting nonsurgical cancer locations [3]. Howe- ver, the procedure is uncomfortable, and it carries a risk Korean J Urol 2011;52:572-577