Analysis of three-dimensional ultrasound Doppler for the detection of prostate cancer

New prospective for non-invasive detection, grading, size evaluation, and tumor location of prostate cancer

BACKGROUND

PSA blood test and other present screening tools fail to provide the required sensitivity and specificity and, at early stages, lack correlation with tumor grade, volume, and location. Thus alternative approaches are highly desired. We present and assess a novel method for PCa detection, grading, volume evaluation and tumor location, based on non-invasive zinc concentration mapping in the gland by means of a dedicated rectal probe.

METHODS

Zinc-concentration values measured in histologically examined tissue fragments from needle biopsy of 598 patients were analyzed. They were used to generate computer simulated zinc-concentration maps, further analyzed with image-processing tools. The tumor detection performances versus Gleason grade were assessed.

RESULTS

A significant increase of zinc depletion with increasing Gleason pattern (grade) classification was established. Tumor detection performance in zinc-concentration maps progressively improves with the cancer's first component score. Reliable information on the location, size and Gleason-grade combination of the lesion can be extracted for clinically relevant volumes.

CONCLUSIONS

Zinc depletion in the prostate peripheral zone is the basis for a novel, non-invasive PCa detection, localization, volume evaluation and grading method. Its realization and application as a pre-biopsy and pre-treatment examination, or a follow-up tool, relies on the development of a dedicated transrectal probe. It should have significant impact on biopsy effectiveness, point at a possible extraprostatic extension and provide critical data for focal treatment. The information on tumor grade and distribution may have an important impact on disease management.

Evaluating the cancer detection and grading potential of prostatic-zinc imaging: a simulation study

The present work deals with the analysis of prostatic-zinc-concentration images. The goal is to evaluate potential clinically relevant information that can be extracted from such images. In the absence of experimental images, synthetic ones are produced from clinically measured zinc-concentration distributions in certified benign and cancerous tissue samples, classified by the lesion grade. We describe the method for producing the images and model the effect of counting statistics noise. We present in detail the image analysis, which is based on a combination of standard image processing and segmentation tools, optimized for this particular application. The information on lowest zinc value obtained from the image analysis is translated to clinical data such as tumour presence, location, size and grade. Their confidence is evaluated with the help of standard statistical tools such as receiver operating characteristic analysis. The present work predicts a potential for detecting small prostate-cancer lesions, of grade (4+3) and above, with very good specificity and sensitivity. The present analysis further provides data on the pixel size and image counting statistics requested from the trans-rectal probe that will record in vivo prostatic-zinc maps in patients.

Computer-aided diagnosis of prostate cancer with emphasis on ultrasound-based approaches: a review

This paper reviews the state of the art in computer-aided diagnosis of prostate cancer and focuses, in particular, on ultrasound-based techniques for detection of cancer in prostate tissue. The current standard procedure for diagnosis of prostate cancer, i.e., ultrasound-guided biopsy followed by histopathological analysis of tissue samples, is invasive and produces a high rate of false negatives resulting in the need for repeated trials. It is against these backdrops that the search for new methods to diagnose prostate cancer continues. Image-based approaches (such as MRI, ultrasound and elastography) represent a major research trend for diagnosis of prostate cancer. Due to the integration of ultrasound imaging in the current clinical procedure for detection of prostate cancer, we specifically provide a more detailed review of methodologies that use ultrasound RF-spectrum parameters, B-scan texture features and Doppler measures for prostate tissue characterization. We present current and future directions of research aimed at computer-aided detection of prostate cancer and conclude that ultrasound is likely to play an important role in the field.

Rapid 3D imaging of contrast flow: demonstration of a dual beam technique

Perfusion imaging in a 3D volume using ultrasound contrast agent may improve vascular characterization compared with 2D imaging. Conventional 3D acquisition requires excessive scan time. A dual transducer technique using conventional systems has been introduced that allows 3D imaging of contrast dynamics with drastically reduced scan times (LeCarpentier et al. 2003). Two transducers are translated across a volume where the leading transducer effects contrast clearance and the following transducer images at desired contrast refill times. With 2D arrays that allow simultaneous clearance and imaging pulses, scan times could be further reduced and the need for two transducers eliminated. The dual transducer technique was demonstrated on a tube phantom, with observed contrast profiles matching those expected. Measured center velocities of (+/- std dev) 1.46 +/- 0.21 and 2.25 +/- 0.5 did not statistically differ from expected values of 1.75 and 2.50 (all mm/s), (p > 0.05). This technique is introduced for rapid acquisition of 3D contrast refill images.

Three dimensional ultrasound and prostate cancer

Three-dimensional ultrasound (3-D US) is a non-invasive method of producing whole volume images of solid structures. Early work on prostate imaging identified several advantages over 2-D imaging with a good ability to detect intraprostatic lesions. Several 3-D transrectal ultrasound (3-D TRUS) systems are now available for prostate imaging. Initial work using gray scale ultrasound appears promising with reported overall staging accuracies of up to 94%. These results were favourable when compared to other modalities for local staging of prostate cancer. Several adjuncts to 3-D gray scale TRUS have been investigated. A greater sensitivity for cancer detection has been achieved with the addition of power colour Doppler and contrast agents. Further clinical applications for 3-D TRUS include assessing placement of brachytherapy seeds and for cyroablation techniques. Computer enhancement with image registration has shown that 3-D US images can be manipulated to derive more information. Although the results of gray scale imaging alone or with adjuncts and post processing appear promising, these techniques remain largely experimental.

Imaging clinically localized prostate cancer

At this time there is no highly sensitive and specific widespread radiographic test for local staging of prostate cancer. Future developments will likely require a combination of imaging modalities with utilization guided by risk-stratification models (Table 4). Staging data for all imaging tests discussed in this article are summarized in Tables 5 and 6. Clinically, conventional gray-scale TRUS remains the most frequently used tool because of its utility in guiding prostatic biopsies. Modifications of TRUS--including power and color Doppler, 3D imaging, and new ultrasound contrast agents and elastography--show promise in increasing the accuracy of ultrasound. Endorectal MRI may have some value for staging selected patients. The addition of prostatic MRS, which images the differential activity of metabolites, may increase the specificity of MRI. Newer techniques with finer voxel resolution may prove to be clinically useful. A large well-designed study evaluating the utility of MRI/MRS is currently being planned. Cross-sectional imaging of the pelvis with either MRI or CT should be used selectively as should radionuclide bone scans. Similarly, ProstaScint scans should be ordered selectively, either before or after primary therapy, rather than routinely in all patients.

Doppler quantitative measures by region to discriminate prostate cancer

This study was conducted to assess if sonographic discrimination between healthy and cancerous prostate tissue might be improved using regional analysis of ultrasound (US) Doppler measures. A total of 39 subjects underwent 3-D Doppler sonography before radical prostatectomy. Cancer locations were identified from hematoxylin and eosin (H&E)-stained slides. Three prostate data volumes consisting of a frequency shift and power-mode Doppler US and whole mount histology images were spatially registered for each prostate, then divided into entirely 1 mL-sized regions of cancerous or noncancerous tissue. Each prostate was visually divided into a peripheral and a periurethral region within which US Doppler measures were calculated. Receiver operating characteristic (ROC) and simulated biopsy analyses within each prostate were performed. Mean speed in colored pixels (V), and speed-weighted pixel density (SWD) are good discriminators for prostate cancer in the periurethral and the peripheral regions, respectively. Using SWD in a simulated biopsy yields increased cancer detection in the peripheral region.