Prostate cancer: correlation of MR images with tissue optical density at pathologic examination

To explain the variability in detection of prostate cancer with magnetic resonance (MR) imaging, the authors correlated preoperative MR findings in 28 patients with tissue optical density (TOD) measurements on whole-mount pathologic slides prepared from radical prostatectomy specimens. TOD was used as an indicator of the degree of tissue compactness or openness. TOD measurements from proved cancers and from pathologic regions corresponding to MR lesions (areas of low signal intensity seen at T2-weighted MR imaging) were compared with TOD measurements from adjacent, nonmalignant tissue. TOD measurements corresponding to MR lesions were higher than noncancerous tissue measurements in all cases (P less than .005). Although most of these lesions represented cancers (21 of 30), nine of 30 represented benign tissue that was composed mainly of densely packed fibromuscular stroma (30% false-positive results). Thus, signal intensity appeared to be related to TOD rather than to a specific histologic tissue type, and the finding of a peripheral zone lesion with low signal intensity did not necessarily indicate the presence of a cancer.     

Renal cell cancer: Incidence of hemorrhage on MR images in patients with chronic renal insufficiency

This study describes the occurrence of hemorrhage in renal cancer in patients with chronic renal insufficiency as shown on MR images. Thirteen consecutive patients with chronic renal insufficiency who had his tologically proven renal cancer and underwent MRI at 1.5 T were entered in the study. MR examinations included spoiled gradient echo (SGE) and T1-weighted fat-suppressed imaging pre- and postgadolinium administration. All renal cancers were well shown on MR images and were most clearly depicted on postgadolinium T1-weighted fat-suppressed images. Tumors in 12 of 13 patients had regions of high signal intensity on precontrast T1-weighted images. Histology demonstrated intratumoral hemorrhage in all 12 of these patients. Four hemorrhagic tumors were largely cystic on imaging studies. One of these cancers altered in appearance from largely cystic with extensive hemorrhage to largely solid with substantial enhancement after a 2.5-year interval. Renal cancers demonstrated minimal enhancement (11 patients) on early postgadolinium images and were minimally enhanced on delayed images in 10 of 13 tumors. Two renal cancers demonstrated intense enhancement. Renal cancers are well shown on MR images in patients with chronic renal insufficiency. Because of the common occurrence of hemorrhage into renal cancers in patients with renal insufficiency, caution should be exercised when evaluating hemorrhagic cystic lesions in these patients.     

Hyperacute subarachnoid hemorrhage on T2-weighted MR images

We describe a case of hyperacute subarachnoid and intraventricular hemorrhage from a ruptured aneurysm, which occurred while the patient was undergoing MR imaging. Compared with CSF, the blood in the subarachnoid space had slightly lower signal intensity on T2*-weighted gradient-echo images and increased signal intensity on T2-weighted spin-echo images. This finding differs from the generally accepted MR appearance of intracranial hemorrhage and should be recognized to ensure proper patient care.     

Prostate cancer localization with endorectal MR imaging and MR spectroscopic imaging: effect of clinical data on reader accuracy

PURPOSE: To determine the effect of digital rectal examination findings, sextant biopsy results, and prostate-specific antigen (PSA) levels on reader accuracy in the localization of prostate cancer with endorectal magnetic resonance (MR) imaging and MR spectroscopic imaging. MATERIALS AND METHODS: This was a retrospective study of 37 patients (mean age, 57 years) with biopsy-proved prostate cancer. Transverse T1-weighted, transverse high-spatial-resolution, and coronal T2-weighted MR images and MR spectroscopic images were obtained. Two independent readers, unaware of clinical data, recorded the size and location of suspicious peripheral zone tumor nodules on a standardized diagram of the prostate. Readers also recorded their degree of diagnostic confidence for each nodule on a five-point scale. Both readers repeated this interpretation with knowledge of rectal examination findings, sextant biopsy results, and PSA level. Step-section histopathologic findings were the reference standard. Logistic regression analysis with generalized estimating equations was used to correlate tumor detection with clinical data, and alternative free-response receiver operating characteristic (AFROC) curve analysis was used to examine the overall effect of clinical data on all positive results. RESULTS: Fifty-one peripheral zone tumor nodules were identified at histopathologic evaluation. Logistic regression analysis showed awareness of clinical data significantly improved tumor detection rate (P <.02) from 15 to 19 nodules for reader 1 and from 13 to 19 nodules for reader 2 (27%-37% overall) by using both size and location criteria. AFROC analysis showed no significant change in overall reader performance because there was an associated increase in the number of false-positive findings with awareness of clinical data, from 11 to 21 for reader 1 and from 16 to 25 for reader 2. CONCLUSION: Awareness of clinical data significantly improves reader detection of prostate cancer nodules with endorectal MR imaging and MR spectroscopic imaging, but there is no overall change in reader accuracy, because of an associated increase in false-positive findings. A stricter definition of a true-positive result is associated with reduced sensitivity for prostate cancer nodule detection.     

Nonacute subdural hematoma: fundamental interpretation of MR images based on biochemical and in vitro MR analysis

Few reports have described the nature of the appearance of nonacute subdural hematoma on magnetic resonance (MR) images. The authors analyzed MR images in 39 cases of nonacute subdural hematoma and subdural effusion by measuring in vitro proton relaxation times and the biochemical variables of hematoma fluids. T1 became proportionally shorter than T2 with an increase in hematocrit but the direct cause of the variation in T1 and T2 was the amount of methemoglobin. The free iron content, not the bound iron content, was another main cause for shortened T1 and T2. Paradoxical findings in the correlation between the total protein or albumin concentration and relaxation times were noted. It is possible that as the protein level in the supernatant increased, more free iron was bound to the protein, decreasing the influence of the free iron on the relaxation times.     

Subacute intracranial hemorrhage: contribution of spin density to appearance on spin-echo MR images

The T2 and pseudodensity (proportional to proton density) of intracranial hemorrhages and normal white matter were calculated. The mean T2 (+/- standard deviation) was 120 +/- 62 for hemorrhage and 61 +/- 11 for white matter. Pseudodensity values were normalized to a white matter value of 1, and the value for hemorrhage was 1.56 +/- 0.28. These values were used to determine which components of hemorrhage-white matter contrast are due to T1, T2, and density. The results indicate that on spin-echo (SE) images obtained with a long repetition time (TR)/short echo time (TE) (2,500/0-20 [TR msec/TE msec]), the contrast is mainly due to density differences, with a modest T2 contribution on 20-msec-TE images and nearly no T1 component. At 600/0-20, the contrast continues to be largely determined by density differences, again with a modest T2 component on 20-msec-TE images. If the T1 of hemorrhage is extremely short, the T1 component of contrast on 600/0-20 SE images will be somewhat greater than the density component. Because contrast on short TR/short TE images may be largely or entirely determined by pseudodensity or T2, it is inaccurate to refer to 600/20 images as "T1-weighted". The assumption that high signal intensity at this sequence implies a "short T1" will lead to misleading conclusions.     

Prostate cancer tumor volume: measurement with endorectal MR and MR spectroscopic imaging

PURPOSE: To determine accuracy of magnetic resonance (MR) and three-dimensional (3D) MR spectroscopic imaging in prostate cancer tumor volume measurement. MATERIALS AND METHODS: Endorectal MR and 3D MR spectroscopic imaging were performed in 37 patients before radical prostatectomy. Two independent readers recorded peripheral zone tumor nodule location and volume. Results were analyzed with step-section histopathologic tumor localization and volume measurement as the standard. Accuracy of tumor volume measurement was assessed with the Pearson correlation coefficient. P values were calculated with a random effects model. Bland-Altman regression analysis was used to evaluate systematic bias between tumor volumes measured with MR imaging and true tumor volumes. Analyses were performed for all nodules and nodules greater than 0.50 cm(3). RESULTS: Mean volume of peripheral zone tumor nodules (n = 51) was 0.79 cm(3) (range, 0.02-3.70 cm(3)). Two readers detected 20 (65%) and 23 (74%) of 31 peripheral zone tumor nodules greater than 0.50 cm(3). For these nodules, measurements of tumor volume with MR imaging, 3D MR spectroscopic imaging, and a combination of both were all positively correlated with histopathologic volume (Pearson correlation coefficients of 0.49, 0.59, and 0.55, respectively); only measurements with 3D MR spectroscopic imaging and a combination of MR and 3D MR spectroscopic imaging demonstrated statistical significance (P <.05). Tumor volume estimation with all three methods was more accurate for higher tumor volumes. CONCLUSION: Addition of 3D MR spectroscopic imaging to MR imaging increases overall accuracy of prostate cancer tumor volume measurement, although measurement variability limits consistent quantitative tumor volume estimation, particularly for small tumors.     

Edge artifacts in MR images: chemical shift effect

The boundaries of some organs as seen in clinical magnetic resonance images appear to be asymmetric. This effect is caused by chemical shift differences between the resonant frequencies of the hydrogen nuclei of water and fat. The zeugmatographic technique maps resonant frequencies to unique spatial locations. These differences in resonant frequencies can appear as artifactual misplacement of information as this one-to-one correspondence is lost. Various phantoms are used to demonstrate that the boundary artifact appears only in the direction of the read (frequency-encoding) gradient when media of two different chemical shifts are separated by an interface. When the relative shift is less than the width of the interface, the boundary appears to be asymmetric; when the relative shift is greater than the width of the interface, a bright band is seen along one edge with a dark band along the other. This artifact is more pronounced in low resolution images than in high resolution images, and these effects are seen even when the relative chemical shift is smaller than a pixel bandwidth. These effects are explained both conceptually and analytically. The clinician should be aware of the potential presence of this artifact at boundary interfaces that bear diagnostic significance.     

Prostate cancer: evaluation with endorectal MR imaging and three-dimensional proton MR spectroscopic imaging

PURPOSE: To establish the additional value of MR Spectroscopy (3D CSI MRS Three-dimensional Chemical Shift Imaging Magnetic Resonance Spectroscopy) to endorectal MR in the diagnosis and grading of prostate cancer. MATERIALS AND METHODS: MR and 3D CSI MR spectroscopy were performed in 53 patients with suspicion of prostate cancer on the basis of rectal exploration and/or transrectal ultrasound and/or the PSA levels. All the examinations were performed with a 1.5 T imager using an endorectal coil. We acquired axial and coronal T2-weighted FSE sequences, axial T1-weighted SE sequences and PRESS 3D CSI (Point Resolved Spectroscopy 3D Chemical Shift Imaging) sequences localized on the axial T2 images so as to include the prostatic gland while excluding the periprostatic fat. The MR examinations were evaluated by two radiologists unaware of the clinical data, transrectal ultrasound findings, PSA levels and histological findings. The MR and 3D CSI MRS findings were compared with the biopsy findings in 22 cases and with material obtained from laparoscopic prostatectomy in 31 cases. RESULTS: The histological examination revealed adenocarcinoma in 37 cases, prostatitis in 2 cases and no alterations in the remaining 14 cases. The morphologic MR scan showed a sensitivity of 76%, a specificity of 56%, an accuracy of 70%, a PPV of 80% and a NPV of 50%. By combining MR and 3D CSI MRS we obtained a sensitivity of 95%, a specificity of 81%, an accuracy of 91%, a PPV of 92% and a NPV of 87%. Elevated choline concentrations were found both in tumours with a low Gleason score (18 cases) and in those with a high Gleason score (19 cases); instead we found markedly reduced (n=9) or absent (n=4) citrate only in the tumours with a high Gleason score, while we found normal citrate levels in the 18 tumours with a low Gleason score. CONCLUSIONS: The 3D CSI MRS improved the reliability of endorectal MR in the diagnosis and characterisation of prostatic cancer. Moreover, the 3D CSI MRS findings demonstrated a linear correlation with tumour grade.     

Prostate cancer: local staging with endorectal surface coil MR imaging

Endorectal surface coil magnetic resonance (MR) imaging was used to stage the local extent of prostate cancer in 22 patients. The endorectal coil images were acquired with a 10-12-cm field of view and a 4-mm section thickness. All pathologic specimens were reviewed by one pathologist. Endorectal surface coil MR imaging was 82% accurate in the differentiation of stage B from stage C cancer. One case was overestimated, and three cases were underestimated. The three underestimated cases consisted of two cases of microscopic capsular invasion and one case of minimal seminal vesicle invasion. In a comparison of retrospective, blinded readings of endorectal coil and body coil images, there was an average improvement in accuracy of 16% in staging prostate cancer with endorectal coil images.     

Prostate cancer: endorectal MR imaging and MR spectroscopic imaging--distinction of true-positive results from chance-detected lesions

PURPOSE: To retrospectively investigate size criteria for the identification of chance-detected lesions at endorectal magnetic resonance (MR) imaging and MR spectroscopic imaging of prostate cancer. MATERIALS AND METHODS: Approval of the committee on human research and written informed consent were obtained. This study was HIPAA compliant. Endorectal MR imaging and MR spectroscopic imaging were performed with a 1.5-T MR imager in 48 men with a mean age of 59 years (age range, 47-75 years) prior to radical prostatectomy. Two independent readers recorded the size and location of all suspected peripheral zone tumor nodules on MR images alone and on images obtained with combined MR imaging and MR spectroscopic imaging. Nodules detected at MR imaging were classified as matched lesions if tumor was present in the same location at step-section histopathologic review. For all matched lesions, kappa values were calculated to examine agreement between measured and actual tumor size. Lesions that were overmeasured at MR imaging with a kappa value of less than 0.2 were considered chance-detected lesions. RESULTS: At MR imaging, two of 27 and four of 35 matched lesions for readers 1 and 2, respectively, were chance-detected lesions. The corresponding numbers of lesions at combined MR imaging and MR spectroscopic imaging were one of 21 and one of 31, respectively. In all but two cases, the measured diameter of chance-detected lesions was more than twice that of the diameter at histopathologic analysis. By using this diameter threshold to distinguish true-positive results, the mean diameter of detected tumors at histopathologic analysis was 15 mm compared with 4 mm for both undetected and chance-detected tumors (P < .05). CONCLUSION: To ensure uniformity in the comparison of scientific studies, peripheral zone tumors detected at MR imaging and MR spectroscopic imaging of the prostate that are in the same location as tumors detected at histopathologic review should be considered chance-detected lesions if the MR transverse diameter is more than twice the histopathologic transverse diameter.     

Arachnoid granulations on high-resolution MR images and diffusion-weighted MR images: normal appearance and frequency

Arachnoid granulations (AGs), protrusions into the cerebral venous sinus lumen, have been reported on cerebral venography, contrast enhanced CT, and conventional MR imaging. Although thin-sliced high-resolution MR images and diffusion-weighted images are frequently obtained, there have been no detailed reports concerning AGs on these images. In this study, the frequency and positional distribution of AGs in the transverse sinus was investigated on thin-sliced high-resolution MR images, and their appearance on diffusion-weighted MR images was evaluated. At least one AG was found in 107 of 151 subjects (70.9%). No statistically significant differences were noticed between males and females or between the right and left sides. No significant correlations between age and size or between age and the number of AGs were noted. On diffusion-weighted images, all AGs showed iso-intensity to normal brain tissue, which was higher than the reported signal intensity of arachnoid cyst and lower than that of epidermoids. In conclusion, AGs are normal structures that are frequently found in the cerebral venous sinuses on high-resolution MR images. Knowledge regarding their frequency and normal appearance would be helpful to avoid confusion between pathological processes and AGs. It is also important to know that AGs are frequently found even in the younger population.     

Os sustentaculi: depiction on MR images

 We describe a 14-year old patient with pain in the medial ankle. The MR study depicted a rare accessory ossicle called the os sustentaculi. This accessory bone should not be confused with a fracture of the sustentaculum tali of the calcaneus.