Amir Fuad Hussain INTRODUCTION Prostate cancer: More common in Western vs Asian countries However, high incidence is seen among Asian immigrants to Western countries within one generation possible predisposing environmental factors In Malaysia, 6 th most frequent cancer & accounts for 5.7% of cancers in males In Malaysia, among the major ethnic groups, the Chinese record the highest incidence of this cancer possible predisposing genetic factors A diet high in fats also associated with a higher incidence Source: Malaysian Oncological Society website URL: http://www.malaysiaoncology.org/article.php?aid=32 INTRODUCTION Prostate cancer: Symptoms dysuria, haematuria, urgency+/ frequency of micturition, bone pain Diagnosis combination of DRE & PSA. MRI findings alone are non specific and may be similar to prostatitis, prostatic abscess & BPH Confirmation of diagnosis Transrectal biopsy under ultrasound guidance Staging CT, MRI, Bone scan Treatment: Surgery, Hormonal treatment, radiotherapy Source: Malaysian Oncological Society website URL: http://www.malaysiaoncology.org/article.php?aid=32 INTRODUCTION Imaging in Prostate cancer: CT conventional thorax, abdomen, pelvis to look for metastases MRI to assess intrapelvic disease Bone scan to assess distribution of bony metastases Source: Malaysian Oncological Society website URL: http://www.malaysiaoncology.org/article.php?aid=32
PROSTATE MRI Is the most accurate non invasive method for staging local extent of prostate ca Has become the definitive test for determining treatment options (e.g. surgery vs radiotherapy) Development of the endorectal coil has increased the accuracy of detection to 82% (compared to 66 69% using the body coil) PROSTATE MRI The combination of conventional T2 weighted sequences AND MR Spectroscopy has been shown to improve cancer detection, localization of cancers in the peripheral & transitional zones of the prostate Combination MR + MRS: Sensitivity 91% Specificity 95% MR alone: Sensitivity 77% Specificity 81% Source: R Harris, A Schned, J Heaney Staging of Prostate Cancer with Endorectal MR Imaging: Lessons from a learning curve Radiographics 1995 Vol 15 No 4 Source: Choi et al Functional MR Imaging of Prostate Cancer Radiographics 2007 Vol 27 No 1 PROSTATE MRI advantages of MRI over other imaging modalities It does not use ionizing radiation. It can obtain images in sagittal, coronal, axial, and/or oblique planes. It provides more soft tissue contrast than other radiological techniques, and PC has low signal intensity as compared to surrounding regions of healthy tissue. This decrease in signal intensity is due to differences in structure between cancerous and normal prostate tissue. Endorectal/pelvic phased array coil MRI has demonstrated higher accuracy than other modalities in assessing seminal vesicle invasion and extra capsular extension (ECE) of PC (96% and 81%r respectively)* Within the same exam, endorectal MRI can also be used to assess the *Source: possibility Hricak H, of White PC spread S, Vigneron to D, lymph et al: Carcinoma nodesof and the prostate bones gland: within MR imaging the pelvis with and close to the prostate. pelvic phased array coils versus integrated endorectal pelvic phased array coils. Radiology 193:703 9, 1994 PROSTATE MRI ANATOMY On T1 weighted MR images, the normal prostate gland demonstrates homogeneous intermediate tolow signal intensity. However T1 weighted MR imaging has insufficient soft tissue contrast resolution for visualizing the intraprostatic anatomy or abnormality. PROSTATE MRI ANATOMY The zonal anatomy of the prostate gland is best depicted on high resolution T2 weighted images. On T2 weighted images, the normal peripheral zone demonstrates a high signal intensity. The signal intensities in the central and transition zones are lower than those in the peripheral zone. The anterior fibromuscular stroma has low signal intensity.
PROSTATE MRI ANATOMY Appearance of Prostate Ca on MRI Appearance of Prostate Ca on MRI On T2 weighted images, prostate cancer usually demonstrates low signal intensity in contrast to the high signal intensity of the normal peripheral zone. On T2 weighted images, prostate cancer usually demonstrates low signal intensity in contrast to the high signal intensity of the normal peripheral zone. However this finding is not specific. Hemorrhage, prostatitis, scarring, radiotherapy, cryosurgery, and hormonal therapy can all result in low T2 signal intensity in the peripheral zone. Secondly, some tumors are isointense to the normal peripheral zone on T2 weighted images, and this accounts in part for the consistent finding that MRI is not 100% sensitive. Appearance of Prostate Ca on MRI Over the last decade, in vivo Magnetic Resonance Spectroscopy (MRS) has emerged as a valuable technique for evaluating tissue levels of various metabolites. This facilitates lesion characterization, such as the differentiation of benign and malignant tissue, and also helps in assessing disease progression and treatment response. MR Spectroscopy of the Prostate In routine MRI, only protons from fat and water molecules contribute to tissue signal, because the contribution from nuclei in other molecules is so tiny. Using MRS, the signal from these other molecules can be detected, allowing noninvasive in vivo assessment of the level of various metabolites within the tissue. Clinically, this technique has been used most commonly in the brain as in MRI brain spectroscopy.
MR Spectroscopy of the Prostate MR Spectroscopy of the prostate In MRSI, prostate cancer is characterized by elevated levels of choline (a normal cell membrane constituent, which is elevated in many tumors) or reduced levels of citrate (a constituent of normal prostatic tissue) or both. The ratio of choline and creatine to citrate in normally healthy prostatic tissue has been established as 0.22 +/ 0.13. Tumor voxel from center of lesion showing pathologic ratio of high (choline + creatine) / citrate as compared to normal healthy tissue. IMAGING PROTOCOL Hardware & software MRI 1.5T Body coil Endorectal coil Software for MR Spectroscopy No contrast needed IMAGING PROTOCOL Sequences Standard sequences UMMC Axial T1 weighted pelvis Axial T2 weighted pelvis Sagital T2 weighted pelvis Coronal T2 weighted prostate MR Spectroscopy of selected volumes of the prostate Others: *Diffusion weighted imaging *Dynamic contrast enhancement *Data mixed on accuracy/specificity of these techniques
Evaluation of MR Images in Prostate Carcinoma Carcinoma usually from PZ appear as hypointense lesion Extracapsular extension : irregular bulging of the prostatic outline, breach of the capsule with extracapsular spread, asymmetry of the neurovascular bundles, and loss of the rectoprostatic angle. Invasion of seminal vesicles Contiguous areas of low signal intensity extending into the seminal vesicles from the base of the prostate (Note this also may be seen postradiotherapy & post biopsy) Invasion of bladder/rectum Lymph nodes lymph nodes >1 cm considered involved T2 weighted axial MRI Hypointense lesion in the peripheral zone Axial T2WI Axial T2WI Hypointense lesion in the right PZ, with focal bulge and loss of the rectoprostatic angle Extracapsular extension and involvement of the neurovascular bundle Benign prostatic hypertrophy Nodular enlargement of the transitional zone Compression of the PZ Low intensity fibrous capsule Coronal T2WI Benign prostatic hypertrophy Enlarged transitional zone Normal deliniation of zonal anatomy on T2WI Coronal T2WI nodular hypointense lesions in the PZ Carcinoma
Coronal T2WI Hypointensity within the right seminal vesicle seminal vesicle involvement Abnormally high Ch+Cr/Ci ratiocarcinoma Normal Ci peak higher than Ch_CR = Thank you