Value of magnetic resonance imaging in prostate cancer diagnosis

Modified Reduced Field-of-View Diffusion-Weighted Magnetic Resonance Imaging of the Prostate: Comparison With Reduced Field-of-View Imaging and Single Shot Echo-Planar Imaging

OBJECTIVE

The objective of this study was to compare the image quality and apparent diffusion coefficient (ADC) of diffusion-weighted imaging (DWI) with modified reduced field of view (FOV) based on 2-dimensional (2D)-selective radiofrequency excitations by tilting the excitation plane in prostate with reduced FOV using parallel-transmit-accelerated 2D-selective radiofrequency excitation and single-shot echo planar imaging (ssEPI).

METHODS

Fifty patients who underwent multiparametric magnetic resonance imaging including 3 DWIs were included. Two observers independently performed qualitative image analyses using 5-point scale. Apparent diffusion coefficient measurements were performed for quantitative analysis.

RESULTS

Modified reduced FOV provided the highest qualitative scores for all categories compared with reduced FOV and ssEPI (P < 0.000). Both reduced FOV DWIs showed higher ADC values compared with ssEPI (P < 0.001); however, the ADC ratios between the lesion and peripheral zone were not significantly different (all P > 0.05).

CONCLUSIONS

The modified reduced FOV DWI showed better overall image quality, differentiability of anatomic regions, and lesion conspicuity with fewer artifacts compared with DWI with reduced FOV and ssEPI.

Does Prostate HistoScanning™ accurately identify prostate cancer, measure tumour volume and assess pathological stage prior to radical prostatectomy?

Objective

The objective of this paper is to assess the ability of Prostate HistoScanning™ (PHS) to accurately identify tumour volume, index lesion characteristics and pathological stage. PHS is a novel technology employing transrectal ultrasound scanning and software analysis of radiofrequency data to produce signatures for benign and cancerous tissues. Recent reports have suggested PHS is capable of characterising the index cancer lesion and disease multifocality and detecting extraprostatic extension (EPE).

Materials and methods

The index test was preoperative PHS on patients undergoing radical prostatectomy (RP). The reference test was the whole-mount pathological analysis of the RP specimen. PHS analysis estimated total tumour volumes, tumour volumes by prostate sextant, the locations and volumes of index lesions, and the presence and location of EPE.

Results

There was no correlation between PHS and histology total tumour volume estimates (Pearson coefficient –0.099), despite accounting for specimen fixation shrinkage (Pearson coefficient –0.070), nor among 144 prostate sextants in 24 patients (Pearson coefficient 0.14). Sensitivity and specificity of PHS in detecting foci > 0.2 ml were 63% and 53%, respectively; and 37% and 71%, respectively, for foci > 0.5 ml. Pearson correlation coefficient for index lesion volumes identified at pathology vs PHS was 0.065. PHS failed to locate accurately index lesion and pathological EPE.

Conclusions

PHS fails to identify total tumour volumes, tumour volumes prostate sextant, index lesion volumes and locations, and presence and location of EPE compared to RP pathology. PHS appears unsuitable for routine diagnostic clinical use in prostate cancer.

Towards Personalized Statistical Deformable Model and Hybrid Point Matching for Robust MR-TRUS Registration

Registration and fusion of magnetic resonance (MR) and 3D transrectal ultrasound (TRUS) images of the prostate gland can provide high-quality guidance for prostate interventions. However, accurate MR-TRUS registration remains a challenging task, due to the great intensity variation between two modalities, the lack of intrinsic fiducials within the prostate, the large gland deformation caused by the TRUS probe insertion, and distinctive biomechanical properties in patients and prostate zones. To address these challenges, a personalized model-to-surface registration approach is proposed in this study. The main contributions of this paper can be threefold. First, a new personalized statistical deformable model (PSDM) is proposed with the finite element analysis and the patient-specific tissue parameters measured from the ultrasound elastography. Second, a hybrid point matching method is developed by introducing the modality independent neighborhood descriptor (MIND) to weight the Euclidean distance between points to establish reliable surface point correspondence. Third, the hybrid point matching is further guided by the PSDM for more physically plausible deformation estimation. Eighteen sets of patient data are included to test the efficacy of the proposed method. The experimental results demonstrate that our approach provides more accurate and robust MR-TRUS registration than state-of-the-art methods do. The averaged target registration error is 1.44 mm, which meets the clinical requirement of 1.9 mm for the accurate tumor volume detection. It can be concluded that the presented method can effectively fuse the heterogeneous image information in the elastography, MR, and TRUS to attain satisfactory image alignment performance.

Multiparametric MRI-targeted TRUS prostate biopsies using visual registration

Prebiopsy multiparametric prostate MRI (mp-MRI), followed by transrectal ultrasound-guided (TRUS-G) target biopsies (TB) of the prostate is a key combination for the diagnosis of clinically significant prostate cancers (CSPCa), to avoid prostate cancer (PCa) overtreatment. Several techniques are available for guiding TB to the suspicious mp-MRI targets, but the simplest, cheapest, and easiest to learn is “cognitive,” with visual registration of MRI and TRUS data. This review details the successive steps of the method (target detection, mp-MRI reporting, intermodality fusion, TRUS guidance to target, sampling simulation, sampling, TRUS session reporting, and quality insurance), how to optimize each, and the global indications of mp-MRI-targeted biopsies. We discuss the diagnostic yield of visually-registered TB in comparison with conventional biopsy, and TB performed using other registration methods.

Novel trends in transrectal ultrasound imaging of prostate gland carcinoma

Carcinoma of the prostate gland is the most common neoplasm in men. Its treatment depends on multiple factors among which local staging plays a significant role. The basic method is transrectal ultrasound imaging. This examination enables imaging of the prostate gland and its abnormalities, but it also allows ultrasound-guided biopsies to be conducted. A conventional gray-scale ultrasound examination enables assessment of the size, echostructure and outlines of the anatomic capsule, but in many cases, neoplastic lesions cannot be observed. For this reason, new sonographic techniques are implemented in order to facilitate detectability of cancer. The usage of contrast agents during transrectal ultrasound examination must be emphasized since, in combination with color Doppler, it facilitates detection of cancerous lesions by visualizing flow which is not observable without contrast enhancement. Elastography, in turn, is a different solution. It uses the differences in tissue elasticity between a neoplastic region and normal prostatic parenchyma that surrounds it. This technique facilitates detection of lesions irrespective of their echogenicity and thereby supplements conventional transrectal examinations. However, the size of the prostate gland and its relatively far location from the transducer may constitute limitations to the effectiveness of elastography. Moreover, the manner of conducting such an examination depends on the examiner and his or her subjective assessment. Another method, which falls within the novel, popular trend of combining imaging methods, is fusion of magnetic resonance imaging and transrectal sonography. The application of multidimensional magnetic resonance imaging, which is currently believed to be the best method for prostate cancer staging, in combination with the availability of a TRUS examination and the possibility of monitoring biopsies in real-time sonography is a promising alternative, but it is associated with higher costs and longer duration of the examination. This paper presents the most important novel trends in transrectal imaging in prostate cancer diagnosis based on the review of the articles available in the PubMed base and published after 2010.

High-resolution diffusion-weighted imaging of the prostate

OBJECTIVE

The purpose of this study was to evaluate the effect of increasing the spatial resolution of the prostate DWI protocol on image quality and lesion conspicuity.

SUBJECTS AND METHODS

Twenty-nine patients with biopsy-proven prostate cancer undergoing MRI examinations were imaged with two diffusion-weighted imaging (DWI) protocols: current standard clinical protocol (6.7 mm(3) voxels) and a new high-resolution protocol (3.1 mm(3) voxels). Diffusion-weighted images were independently and subjectively scored on lesion conspicuity, internal architecture definition, and overall image quality by two radiologists. Average apparent diffusion coefficient (ADC) values were measured in normal tissue and cancerous lesions on both sequences. Reader scores and ADC and contrast values were compared between the two protocols. Cancer ADC values were correlated with Gleason scores.

RESULTS

The signal-to-noise ratio of the new high-resolution DWI protocol was 40% lower than that of the standard protocol. The reader scores were higher by 0.73 (range, 0.29-1.16) grades, or 19% (range, 7-32%), on average, for the new protocol, indicating better image quality. The average ADC values were 8% higher with the new protocol, with ADC contrast values between cancer and normal prostate unchanged. There was marginally significant correlation of cancer ADC values with Gleason scores (p = 0.05, r ≈ -0.36).

CONCLUSION

We showed that for DWI of the prostate at 3-7 mm(3) voxel sizes the benefits of higher spatial resolution outweigh the effects of reduced signal-to-noise and contrast-to-noise ratios, potentially improving the sensitivity to small or sparse prostate cancers. Radiologists can consider using higher-spatial-resolution DWI sequences in their practices.

Evaluation of the normal-to-diseased apparent diffusion coefficient ratio as an indicator of prostate cancer aggressiveness

Background

We tested the feasibility of a simple method for assessment of prostate cancer (PCa) aggressiveness using diffusion-weighted magnetic resonance imaging (MRI) to calculate apparent diffusion coefficient (ADC) ratios between prostate cancer and healthy prostatic tissue.

Methods

The requirement for institutional review board approval was waived. A set of 20 standardized core transperineal saturation biopsy specimens served as the reference standard for placement of regions of interest on ADC maps in tumorous and normal prostatic tissue of 22 men with PCa (median Gleason score: 7; range, 6–9). A total of 128 positive sectors were included for evaluation. Two diagnostic ratios were computed between tumor ADCs and normal sector ADCs: the ADC peripheral ratio (the ratio between tumor ADC and normal peripheral zone tissue, ADC-PR), and the ADC central ratio (the ratio between tumor ADC and normal central zone tissue, ADC-CR). The performance of the two ratios in detecting high-risk tumor foci (Gleason 8 and 9) was assessed using the area under the receiver operating characteristic curve (AUC).

Results

Both ADC ratios presented significantly lower values in high-risk tumors (0.48 ± 0.13 for ADC-CR and 0.40 ± 0.09 for ADC-PR) compared with low-risk tumors (0.66 ± 0.17 for ADC-CR and 0.54 ± 0.09 for ADC-PR) (p < 0.001) and had better diagnostic performance (ADC-CR AUC = 0.77, sensitivity = 82.2%, specificity = 66.7% and ADC-PR AUC = 0.90, sensitivity = 93.7%, specificity = 80%) than stand-alone tumor ADCs (AUC of 0.75, sensitivity = 72.7%, specificity = 70.6%) for identifying high-risk lesions.

Conclusions

The ADC ratio as an intrapatient-normalized diagnostic tool may be better in detecting high-grade lesions compared with analysis based on tumor ADCs alone, and may reduce the rate of biopsies.

Importance of HOX genes in normal prostate gland formation, prostate cancer development and its early detection

The aims of this paper were to review the published literature on the role of HOX genes in the development of the normal prostate gland and in prostate cancer and to discuss the potential role of the HOX family member, Engrailed-2 (EN2), as a diagnostic test of PCa. Hox genes were first described in the fruit fly Drosphila melanogaster, where they specify the body plan and control the formation of body segments. They belong to a family of homeodomain-containing transcription factors that determine cell and tissue identity during normal embryonic development. They have been shown to be re-expressed by several different types of cancers. Studies have shown that different Hox genes are responsible for the development of the separate lobes of the prostate gland, the seminal vesicles and the epididymis. All HOX13 paralogues are expressed in the adult human prostate, suggesting the possibility of similarities between the function and expression of HOX genes within urological structures at similar anterior-posterior positions. The oncogenic and tumour suppressor signalling pathways associated with PCa converge on the HOX gene network, which ultimately controls gene expression, affecting tumour formation and metastatic progression. The Engrailed genes (EN1 and EN2) from the HOX gene family show a very high degree of functional conservation during embryonic development. Urinary EN2 is being investigated as a potential diagnostic marker of early PCa. It is secreted into the urine by PCa cells but not by normal prostatic tissue. A recent study has shown an association between urinary EN2 levels and cancer volume in radical prostatectomy specimens. The ability to predict tumour volume could inform the treatment decision-making process for patients with localized PCa choosing between active surveillance and radical treatment options.

Accuracy of preoperative endorectal MRI in predicting extracapsular extension and influence on neurovascular bundle sparing in radical prostatectomy

PURPOSE

To evaluate the accuracy of presurgical endorectal MRI (eMRI) for local staging before radical prostatectomy (RP) and its influence on neurovascular bundle (NVB) resection during radical prostatectomy.

PATIENTS AND METHODS

A total of 385 patients with histologically proven prostate cancer (PCa) have been included in this retrospective study between 2004 and 2008. All patients underwent preoperative eMRI at 1.5 T before open RP. Staging results by eMRI were compared with the histopathological findings. The presence of positive surgical margins and extent of nerve-sparing procedure were evaluated. Subgroup analysis of low-risk group and intermediate to high-risk group based on D'Amico criteria was conducted.

RESULTS

In 294 (76.4%) patients, pathological stage was correctly predicted, 69 patients (17.9%) were understaged and 22 (5.7%) overstaged. Overall sensitivity, specificity, negative and positive predictive value for predicting extracapsular extension (ECE) were 41.5, 91.8, 78.0 and 69.0%, respectively. One hundred and fifty-two (48.4%) of the patients classified as stage cT2 by eMRI underwent bilateral NVB sparing, whereas 14 (19.7%) patients with reported ECE underwent bilateral NVB sparing (P < 0.01). Overall positive surgical margin rate was 14.8%. Sensitivity of predicting ECE and positive predictive value were lower in the low-risk group than in the intermediate and high-risk group.

CONCLUSIONS

eMRI is effective in predicting extracapsular extension in an intermediate to high-risk group. Preoperative eMRI in patients with low-risk criteria is not recommended as a routine assessment modality. eMRI findings did appear to influence surgical strategy as patients with imaging findings suggesting >cT2 disease were less likely to undergo NVB sparing.

Vascular endothelial growth factor receptor 2-specific microbubbles for molecular ultrasound detection of prostate cancer in a rat model

OBJECTIVES

To investigate whether rat prostate cancer can be detected by means of molecular ultrasound (US) using target-specific microbubbles versus a nonspecific contrast agent.

MATERIALS AND METHODS

A total of 20 Copenhagen rats were randomly examined 75 to 104 days after orthotopic implantation of G-Dunning rat prostatic tumor cells was using a high-end US system and either 1.2 mL/kg of the nonspecific agent A or 0.1 mL/kg of the target-specific agent B, containing vascular endothelial growth factor receptor 2 binding peptide. Contrast inflow (areas under the curve analysis) was determined during the first 30s, and all microbubbles were destroyed in the scan plane by means of the flash technique 20 minutes after intravenous administration to investigate specific accumulation of individual bubbles in tumors. Differences between normal prostate tissue and tumor were analyzed using luminance images. Sonographically determined tumor localization and extent were compared with magnetic resonance imaging and histology.

RESULTS

The median tumor size in the 20 rats determined on US (2.3 mm) and magnetic resonance imaging (2.4 mm) showed a very high correlation (r = 0.92, P = 0.01). Both agent A and agent B demonstrated higher vascularization of tumor periphery compared with normal prostate (P < 0.05) based on contrast inflow and areas under the curve analysis. Twenty minutes after administration, luminance for agent B in the tumor was significantly higher (P = 0.003) compared with nonspecific agent A (11.8-0.1). In consensus reading, the increase in signal intensity of the tumor compared with normal prostate tissue was significantly higher for agent B (P = 0.005), whereas no significant difference was found for agent A (P = 0.180).

CONCLUSIONS

The target-specific contrast agent was superior to the unspecific US contrast agent both with regard to early inflow analysis and specific accumulation in prostate cancer after 20 minutes.

Comparison of real-time sonoelastography with T2-weighted endorectal magnetic resonance imaging for prostate cancer detection

OBJECTIVES

The purpose of this study was to compare the value of real-time sonoelastography with T2-weighted endorectal magnetic resonance imaging (MRI) for prostate cancer detection.

METHODS

Thirty-three patients with an elevated prostate-specific antigen level were investigated with real-time sonoelastography and T2-weighted endorectal MRI for prostate cancer diagnosis before systematic prostate biopsy. Real-time sonoelastography was performed to assess prostate tissue elasticity, and hard areas were considered suspicious for prostate cancer. Low-signal intensity nodules on T2-weighted endorectal MRI were considered suspicious for prostate cancer. Imaging findings were assigned to 6 areas of the peripheral zone (sextants), and their cancer detection rates were compared.

RESULTS

Overall, prostate cancer was detected in 13 of 33 patients (39.4%). Both real-time sonoelastography and T2-weighted endorectal MRI detected 11 cancer-positive patients (84.6%). Real-time sonoelastography showed 27 suspicious lesions in 198 sextants, and 15 (55.6%) were cancer positive. T2-weighted endorectal MRI showed 31 suspicious lesions in 198 sextants, and 13 (40.6%) were cancer positive. These findings resulted in sensitivity rates and negative predictive values per patient of 84.6% and 86.7%, respectively, for sonoelastography and 84.6% and 83.3% for MRI. The per-sextant analysis showed sensitivity rates and negative predictive values of 57.7% and 93.6% for sonoelastography and 50.0% and 92.2% for MRI.

CONCLUSIONS

Real-time sonoelastography showed comparable results as T2-weighted endorectal MRI for prostate cancer detection.

Inapparent tumor on endorectal multimodality magnetic resonance imaging of prostate: should we perform a biopsy?

OBJECTIVES

To examine whether one could spare patients with a clinical suspicion of prostate cancer (PCa) but inapparent tumor on multimodality endorectal magnetic resonance imaging (e-MRI) of the prostate from undergoing prostate biopsy.

METHODS

A total of 109 patients with a clinical suspicion of PCa underwent conventional and functional e-MRI of the prostate and subsequently prostate biopsy. The inclusion criteria were prostate-specific antigen level>4 ng/mL or a suspicious finding on digital rectal examination. The images were interpreted by a highly experienced radiologist and were considered negative for PCa in all cases. Regardless of the negative findings, all patients underwent an 18-core prostate biopsy. Functional e-MRI included contrast-enhanced e-MRI and diffusion-weighted imaging. The examinations were performed on a closed 1.0-T system combined with an endorectal body phased-array coil. The clinicopathologic parameters of the patients included age, prostate-specific antigen level, digital rectal examination findings, PCa detection rate, clinically significant PCa detection rate, high-grade PCa detection rate, and e-MRI specificity.

RESULTS

The median age of the patients was 67.4 years, and the median prostate-specific antigen level was 12.9 ng/mL. The digital rectal examination findings were positive in 42 patients (38.5%) and negative in 67 patients (61.5%). Overall, PCa was detected in 19.2% of patients, with 47.6% cases defined as clinically significant and 38.1% as high grade. Overall, the e-MRI specificity was 80.8%.

CONCLUSIONS

The results of our study have shown that the absence of tumor on e-MRI scans of patients with a clinical suspicion of PCa does not rule out the probability of clinically significant and high-grade PCa, making prostate biopsy mandatory for these patients as well.

Real-time Virtual Sonography for navigation during targeted prostate biopsy using magnetic resonance imaging data

OBJECTIVES

To evaluate the effectiveness of the medical navigation technique, namely, Real-time Virtual Sonography (RVS), for targeted prostate biopsy.

METHODS

Eighty-five patients with suspected prostate cancer lesions using magnetic resonance imaging (MRI) were included in this study. All selected patients had at least one negative result on the previous transrectal biopsies. The acquired MRI volume data were loaded onto a personal computer installed with RVS software, which registers the volumes between MRI and real-time ultrasound data for real-time display. The registered MRI images were displayed adjacent to the ultrasonographic sagittal image on the same computer monitor. The suspected lesions on T2-weighted images were marked with a red circle. At first suspected lesions were biopsied transperineally under real-time navigation with RVS and then followed by the conventional transrectal and transperineal biopsy under spinal anesthesia.

RESULTS

The median age of the patients was 69 years (56-84 years), and the prostate-specific antigen level and prostate volume were 9.9 ng/mL (4.0-34.2) and 37.2 mL (18-141), respectively. Prostate cancer was detected in 52 patients (61%). The biopsy specimens obtained using RVS revealed 45/52 patients (87%) positive for prostate cancer. A total of 192 biopsy cores were obtained using RVS. Sixty-two of these (32%) were positive for prostate cancer, whereas conventional random biopsy revealed cancer only in 75/833 (9%) cores (P < 0.01).

CONCLUSIONS

Targeted prostate biopsy with RVS is very effective to diagnose lesions detected with MRI. This technique only requires additional computer and RVS software and thus is cost-effective. Therefore, RVS-guided prostate biopsy has great potential for better management of prostate cancer patients.

Technologies for localization and diagnosis of prostate cancer

The gold standard for detecting prostate cancer (PCa), systematic biopsy, lacks sensitivity as well as grading accuracy. PSA screening leads to over-treatment of many men, and it is unclear whether screening reduces PCa mortality. This review provides an understanding of the difficulties of localizing and diagnosing PCa. It summarizes recent developments of ultrasound (including elastography) and MRI, and discusses some alternative experimental techniques, such as resonance sensor technology and vibrational spectroscopy. A comparison between the different methods is presented. It is concluded that new ultrasound techniques are promising for targeted biopsy procedures, in order to detect more clinically significant cancers while reducing the number of cores. MRI advances are very promising, but MRI remains expensive and MR-guided biopsy is complex. Resonance sensor technology and vibrational spectroscopy have shown promising results in vitro. There is a need for large prospective multicentre trials that unambiguously prove the clinical benefits of these new techniques.