This application is a continuing application of a co-pending U.S. patent application Ser. No. 12/885,688 filed Sep. 20, 2010 with the same title, which in turn is a continuing application of U.S. patent application Ser. No. 11/146,367 filed on Jun. 6, 2005 with the same title, now U.S. Pat. No. 7,819,824, which in turn is a continuation-in-part of U.S. patent application Ser. No. 11/123,999 filed on May 6, 2005 and entitled “Method and device for real time mechanical imaging of prostate”, now U.S. Pat. No. 7,922,674.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
This invention was made with government support under SBIR Grant 2 R44 CA82620-02A1 awarded by the National Institutes of Health, National Cancer Institute. The government has certain rights in this invention.
BACKGROUND OF THE INVENTION
The present invention relates generally to medical devices. More specifically, it relates to a mechanical imaging system and process for examining, mapping, and diagnosing diseases of a palpable organ such as a prostate gland in a male patient, especially the prostate cancer. It is also applicable more generally to mechanical imaging of palpable tissues, including but not limited to, through natural body openings in a human being, i.e. mouth, ear(s), rectum, and other body cavities. It is also applicable to determination of a relative stiffness or elasticity of tissues. The term “patient” includes human beings and animals, both alive and dead that can be subject to mechanical imaging.
The high incidence of prostate cancer, as well as benign prostatic hyperplasia (BPH), especially among the older male population, dictates the need for effective means of early detection. Prostate cancer is the cause of death in about 30,000 men each year, making it the number two cancer killer of men in the United States, second only to lung cancer. However, if prostate cancer is detected early and treated effectively, the chance of survival of one afflicted with this disease improves significantly. Current methods of early diagnosis of prostate cancer include digital rectal examination (DRE), measurement of serum levels of prostate specific antigen (PSA), and transrectal ultrasound (TRUS) examination.
The following discussion provides useful overview of various methods described in the prior art and applicable to prostate examination and imaging. Substantial prior art is accumulated describing various devices and techniques using ultrasound for the imaging of the prostate. U.S. Pat. No. 6,561,980 by Gheng describes the methods of processing ultrasound images to cause automatic segmentation of prostate, rectum, and urethra once the transverse cross-sectional image of prostate is acquired by ultrasound means. U.S. Pat. No. 6,824,516 by Batten describes a sophisticated system for examining, mapping, diagnosing, and treating prostate diseases based on ultrasonic imaging, this patent is incorporated herein in its entirety by reference. U.S. Pat. No. 6,778,690 by Ladak describes a method of processing 2D and 3D ultrasound images to determine the prostate boundaries and is also incorporated herein by reference in its entirety as it provides useful image processing methodology.
Unfortunately, to date the experience with TRUS as a means of prostate cancer screening and staging has been disappointing. It adds little to screening by DRE and PSA, and the small improvement in prostate cancer detection does not justify its cost. As a screening test, TRUS has a low specificity and a high false positive rate. Evaluation of pathologic specimens shows that a significant fraction of tumors are isoechoic and thus indistinguishable from surrounding tissue, while many palpable tumors could not be visualized by TRUS.
The most sensitive single test for prostate cancer is measurement of serum PSA levels. However, its positive predictive value is limited. The DRE alone is even less useful. However, combining the two modalities nearly doubles the cancer detection rate. Large-scale studies of systematic screening for prostate cancer using PSA, DRE and TRUS concluded that combining PSA and DRE provided the highest sensitivity and specificity for prostate cancer diagnosis. Therefore, the combination of the two methods for prostate cancer screening is currently recommended by the AUA and American Cancer Society, and has been approved by FDA for patients between the ages of 50 and 75 years.
At the present time, digital rectal examination is the most widely used method of prostate cancer screening. Approximately 30-50% of palpable prostate nodules prove to be malignant upon pathologic evaluation. Screening trials have demonstrated that 70% of men with abnormal DRE undergoing radical prostatectomy have organ-confined cancer. A strong association between abnormal DRE and prostate cancer mortality has been demonstrated and it was suggested that screening DRE could prevent as many as 50-70% of deaths due to prostate cancer. DRE also has been shown to be the most cost efficient prostate screening method, especially when combined with PSA.
The main disadvantage of DRE is its high degree of subjectivity. The user has to instinctively relate what he or she senses by the finger to previous DRE experience. There may not be a sufficient number of skilled users available for large-scale mass prostate screenings. Another limitation of DRE is that a physician performing the examination cannot objectively record the state of the examined prostate. Therefore, it is difficult to objectively compare the results of consecutive examinations of the same prostate. The need therefore exists for a device allowing conducting the prostate examination objectively and obtaining results consistently that are independent of the skills of individual operators.
A new method of prostate imaging based on principles similar to those of manual palpation has been developed by Sarvazyan et al. and described in the U.S. Pat. Nos. 6,569,108; 6,142,959; 5,922,018; 5,836,894; 5,785,663; and 5,524,636, as well as in a co-pending U.S. application Ser. No. 11/123,999 all incorporated herein in their entirety by reference. This method, termed Mechanical Imaging, provides the ability to “capture the sense of touch” and store it permanently for later temporal correlation and trending. The essence of mechanical imaging is measurement of the stress pattern on the surface of the compressed tissue and analyzing the changes of that pattern while moving the sensor array over the examined tissue. Temporal and spatial changes in the stress pattern provide information on the mechanical structure of the examined tissue and enable 3D reconstruction of internal structures and mechanical heterogeneities in the tissue. Mechanical imaging is free of many of the disadvantages of DRE. Mechanical imaging has been shown to exceed substantially the limits of lesion size and depth detectable by conventional manual palpation techniques [Weiss R., Hartanto V, Perrotti M, Cummings K, Bykanov A, Egorov V, Sobolevsky S. “In vitro trial of the pilot prototype of the prostate mechanical imaging system”, Urology, V.58, No. 6, 2001, p.1059-1063].
Recently, the American Urological Association issued recommendations to help physicians confirm the diagnosis of prostate cancer. According to these recommendations, a biopsy should be considered for any patient with an abnormal DRE and elevated PSA. The effectiveness and reliability of DRE are highly dependent on the skill of the user, since the finger does not provide a quantitative or objectively verifiable assessment. Thus, there is a great need for a new technology and a device to enable general practitioners and urologists alike to perform a reliable, accurate, sensitive, and quantitative assessment of the prostate using a computerized palpation-imaging device. Moreover, such accurate assessment of prostate size, shape, and elasticity is also important for diagnosing and monitoring of prostate cancer and BPH. Mechanical imaging technology and the low cost, prostate imaging device should improve significantly the ability of minimally trained individuals in primary care settings to assess, screen, and monitor prostate pathology in a reliable and valid manner in a male human, with a minimum of physical and mental discomfort.
While prior art mechanical imaging devices provided for data collection, the ability to recreate the 2D and 3D images of the prostate were limited by the insufficiently accurate information obtained from the transrectal probe with regard to the examined prostate in the course of examination. One reason for this is the sub-optimal shape of the probe device itself. Prior art probes are predominantly round and cylindrical in shape to repeat that of the rectum. Upon compressing the area about the prostate, it is difficult to obtain uniform compression of that area alone and not load surrounding tissues and organs, especially the sphincter.
The need exists for a novel method and probe adapted for uniform compression of the desired area in the vicinity of the prostate gland without compressing surrounding tissues such as a sphincter. Such compression of surrounding tissues and organs would distort data collection away from the desired area and introduce errors associated with tilting the probe and stretching the sphincter or other tissues of the rectum.
Another reason for reduced sensitivity is because the prostate can be hard to find initially and it can also shift from its original place during the examination procedure. Therefore, the prior art methods have a fundamental disadvantage in that as the examination progresses, no means are available to properly locate the prostate and then compensate for the probe position and orientation shift relative for the moving prostate.
The need exists therefore for a prostate examination means and method of use designed to eliminate the distortion in the position data of the prostate probe and make it independent of the internal movements of the prostate organ.
Finally, the need exists for devices and methods allowing training of medical personnel conducting prostate mechanical imaging.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to overcome these and other drawbacks of the prior art by providing a novel method and device for objective and consistent mechanical imaging of a palpable organ eliminating the influence of operator's skills on the results of such examination.
It is another object of the present invention to provide a mechanical imaging device for examination of prostate shaped in such a way as to allow proper compression of the prostate organ only and minimizing distortions caused by pressing the device against other surrounding tissues and organs.
It is another object of the present invention to provide a mechanical imaging device for examination of prostate having dual-array pressure transducer probe, one array on the head of the probe and another on the shaft of the probe.
It is another object of the present invention to provide a probe and a method of its use allowing teaching the medical personnel the proper technique of prostate examination.
The method of the invention is based on a method of real time mechanical imaging of the prostate organ with a probe inserted through a rectum. According to one aspect of the method of the invention, generating a two- or three-dimensional prostate mechanical image from a plurality of pressure response data and probe orientation data comprises the general steps of:
locating the prostate under the transrectal probe head pressure sensor array by first identifying the sphincter with a secondary pressure sensor array located on a probe shaft, then advancing the probe until the bladder is reached and then retracting it somewhat to identify the area of probable location of the prostate,
scanning the prostate by the probe head sensor array by pressing it repeatedly against the prostate,
incorporating newly acquired mechanical prostate information into a two-dimensional normalized mechanical image of the prostate, including using of the sphincter as a secondary reference object,
visualizing that two-dimensional normalized mechanical image of the prostate in real time to reveal possible areas of interest inside the prostate, and
calculating prostate features and constructing of composite two-dimensional and three-dimensional mechanical prostate images, using an image recognition technique.
Importantly, the processing of data is preferably conducted by using data from both the probe head pressure sensor array (used as a primary or first source of pressure data) and from shaft pressure sensor array (used as a secondary source of pressure data). This allows moving of the probe relative to the prostate while maintaining the common identified features of each obtained mechanical image. In other words, every time the probe is moved from one position to the next, the processing means of the device are adapted to follow certain identifiable features and the distance from the sphincter from the previous mechanical image to the next one such that a complete 2D or 3D image may be constructed. That way, there is less need for knowing the absolute position in space of both the prostate and the probe in order to accurately relate each successive pressure pattern to a certain part of the prostate.
In the preferred embodiment, the dual-array probe and the system of the invention include: an S-shaped probe shaft with pressure sensor array for collecting pressure response data in the vicinity of the sphincter; a probe head pressure sensor array for collecting data in the vicinity of the prostate volume; a probe orientation tracking sensors for collecting a probe orientation data; a processing apparatus for processing the pressure response and orientation data to generate mechanical image data and calculate prostate features; and a display device for representation of at least a two-dimensional image of the prostate.
Importantly, the shape and size of the head pressure sensor array is selected such that it provides for uniform compression of the area of interest about the prostate gland and not other areas of the rectum. Further facilitating this aspect of the invention is the S-shaped design and an angular offset between the head of the probe and the shaft of the probe. Such advantageous shape increases the accuracy of obtained pressure data and reduces the artifacts caused by inadvertent tilting of the probe to avoid sphincter trauma.
Preferably, in order to further increase the accuracy of the results, the probe head orientation and its position relative to examined prostate is calculated from orientation data recorded from 3D magnetic sensors and a 2D accelerometer sensor, and combined with the pressure response data recorded from the head pressure sensor array and the shaft pressure sensor array.
As opposed to the devices of the prior art, the present invention takes advantage combining three independent sources of positioning information:
using the prostate itself as a reference object by providing real time calculation and visualization of the probe head positioning relative to the examined prostate
having more than one pressure sensor arrays working together in an integrated manner to take advantage of locating the prostate in its relationship to a nearby organ, which is more stable in its position such as sphincter, and finally
calculating of probe head position from probe orientation data.
Combining all these sources of information, the device of the invention provides calculations including both the orientation and pressure response data. The device and method of the present invention are created with a design philosophy to create a patient-friendly system, which is easy and intuitive to use by the examining physician. As a result, the present invention advantageously provides for:
early prostate cancer detection;
quantitative classification of prostate geometrical and mechanical features;
automatic identification of what has changed between successive examinations;
tracking and trending treatment impact for certain treatment modalities;
matching the system output with pathology findings as proof of system performance.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the subject matter of the present invention and the various advantages thereof can be realized by reference to the following detailed description in which reference is made to the accompanying drawings in which:
FIG. 1 is a schematic diagram illustrating the functional structure of the system in accordance with the present invention,
FIG. 2 is a side view of the probe with a head pressure sensor array, a shaft pressure sensor array, and orientation sensors,
FIGS. 3A and 3B are cross-sectional views of the probe head and the probe shaft respectively in accordance with the present invention,
FIG. 4 is a diagram of an orientation tracking system used in the preferred embodiment of the present invention,
FIG. 5 represents an electronic unit schematic diagram of the device,
FIG. 6 is a flow chart describing steps for obtaining diagnostic information,
FIG. 7 is a perspective view of the transrectal probe relative to an examined prostate, illustrating a reference coordinate system having three orthogonal axes and probe orientation angles,
FIG. 8 is a flow chart describing steps for composition of two-dimensional and three-dimensional prostate mechanical images and calculating prostate features,
FIG. 9 is an illustration of real time two-dimensional prostate image and sphincter area mechanical image with relative probe positioning to guide the use of the probe during prostate examination, and
FIG. 10 is an illustration of a three-dimensional prostate mechanical image composition.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
A detailed description of the present invention follows with reference to accompanying drawings in which like elements are indicated by like reference letters and numerals.
Referring now to the drawings, FIG. 1 is a schematic view of a preferred embodiment of a device for generating a mechanical image of a three-dimensional prostate volume from a plurality of data frames corresponding to a scan of the prostate. The device comprises the following major elements:
a dual-array transrectal probe 3 with incorporated head pressure sensor array 1 for receiving pressure response data for the prostate 4 and shaft pressure sensor array 2 for receiving supplemental pressure response data for a sphincter area 5,
electronic unit 6, and
a processing and displaying means 7, which may be for example incorporated into a compact personal computer.
The prostate examination is performed using the following general steps. The patient is instructed to take off all clothes below the waist. The examination is preferably performed in the standing position by bending a patient over the examination table to form a 90-degree angle at the waist. This novel position allows the muscles in the vicinity of the examination probe to relax and has yielded better results than other examination position. In this position, patient\' chest is lying on the table or another horizontal surface and patient\'s weight is applied to the table surface so that leg muscles are free from any tension. Optionally, the patient can also be examined while lying on his side, with his knees bent toward his chest. The probe is preferably enclosed within a disposable lubricated cover. During the insertion into the rectum, pressure applied to the anal sphincter should be monitored in order to minimize the level of patient\' discomfort. Gentle posterior pressure is applied as the probe is slowly inserted with the sensor surface down. Allowing a few seconds for the external and internal sphincter to relax will avoid patient discomfort. Scanning begins in the sagitall plane by first optionally imaging the sphincter used as a supplemental reference organ. Then, the probe is inserted deeper until the bladder is visualized. Next, by sliding the probe backwards, the prostate is detected and the probe is positioned in a way that enables the device to display the prostate gland surface in the center of the screen. Once the probe is properly positioned, evaluation of prostate is performed through a set of multiple pressings on the median sulcus and lateral lobes of the prostate. In certain cases, change in an elevation angle of the probe is required to visualize the prostate.
FIG. 2 is a side view of the preferred embodiment of the transrectal probe 3 with the head pressure sensor array 1 installed on a probe head 21, and with the shaft pressure sensor array 2 installed on a probe shaft 22 attached to the probe handle 24. The most distal probe head section of the probe has a straight segment containing the head pressure sensor array. The length of this straight segment is preferably chosen to be about 25 mm (1 inch) to about 50 mm (2 inches) long. This length allows proper coverage of the prostate area without interfering with the bladder or other surrounding tissues.
The shaft 22 of the probe has an S-shaped distal end 22a designed to provide a linear offset between the head of the probe and the shaft of the probe. When the probe head is compressed against the prostate, the entire probe is moved somewhat down in the direction of the prostate. The presence of this S-shaped section of the probe shaft allows not to compress tissues and organs surrounding the shaft and only to compress the prostate by pressing the probe head against thereof. Dimensions of the S-shaped distal end of the probe shaft are chosen preferably to ensure that the linear offset between the shaft and the head is ranging between about 4 mm ( 5/32 of an inch) and 15 mm ( 19/32 of an inch). In the most preferred embodiment of the invention this distance is about 10 mm.
Additional improvement in the design of the probe is in the angular offset between the longitudinal axis of the probe head and the longitudinal axis of the probe shaft. Tilting the shaft axis at about 4 to 12 degrees about the head axis further reduces the distortion of the surrounding tissues and organs when the probe head is pressed against the prostate.
Spacing apart the head pressure sensor array and the shaft pressure sensor array at a proper distance allows the probe to be used to find the estimated position of the prostate using the position of the anal sphincter. In the preferred configuration of the dual-array transrectal probe of the invention, the distance between the head pressure array and the shaft pressure array is selected to be about 40 mm (1 9/16 inches) to about 80 mm (3 ⅛ inches) as measured between the centers of the respective pressure sensor arrays. The most preferred distance is about 60 mm as this is the average distance between the sphincter and the center of a prostate.
Optional elastic disposable cover (not shown) may be used to envelop the entire surface of the probe head 21, probe shaft 22, and partly the probe handle 24. The probe handle 24 further comprises supplemental positioning means consisting of a three-axis magnetic sensor 25 and a two-axis accelerometer sensor 26. The probe also includes an examination “start-stop” button 23. Of note here is the offset of the probe head 21 relative to the probe shaft 22. It is designed such that the probe better fits with the anatomy of a human patient—only the head is pressing against the prostate and the shaft is not loading the sphincter with a down aimed force. Both the shaft and the head pressure sensor arrays are therefore better adapted to visualize the prostate and the sphincter respectively.
FIG. 3A is a preferred cross-sectional view of the preferably oblong probe head 21 with surface installed pressure sensors 31 in accordance with the present invention. As opposed to previously known devices of this type having linear pressure sensing arrays, the probe of the invention is equipped with a two-dimensional pressure sensor array. A plurality of pressure sensors 32 constitutes the pressure sensing matrix of the head pressure sensor array 1 as shown in FIG. 2. The two-dimensional pressure sensor array 1 serves the following three main purposes:
providing pressure response data in the course of examination of the prostate,
providing information on changes in the probe head position relative to the prostate deploying a mechanical image recognition technique, and
guiding the user during prostate examination by displaying a real time complete two-dimensional pressure pattern of the head pressure sensor array.
Size, grid, and sensor quantity in the head pressure sensor array may very. Preferably, the head pressure sensor array has a pressure sensitive area of about 12 to 20 mm wide by 30 to 50 mm long, and includes over 100 individual pressure sensors. The curvature radius of the probe head may vary too, but preferably the curvature radius should be about 10 to 20 mm to provide a uniform stress pattern while pressing against the prostate. Individual pressure sensors may be designed to be a piezoelectric, resistive, or quantum tunneling composite pressure transducer, possibly using micro-machined parts or nano-technologies. Preferably, each pressure sensor includes a capacitive pressure transducer covered by an elastic compound.
FIG. 3B is a preferred cross-sectional view of the probe shaft 22 with surface installed supplemental pressure sensors 32 in accordance with the present invention. A plurality of supplemental pressure sensors 32 constitutes the shaft pressure sensor array 2 as shown in FIG. 2. This shaft pressure sensor array serves two main purposes:
receiving supplemental pressure data from the sphincter area needed to guide the user during prostate examination by displaying a real time complete two-dimensional pressure pattern of the shaft pressure sensor array, and
calculating a longitudinal position of the probe head relative to the sphincter allowing an additional correction of the probe head transversal position relative to the prostate, taking into account real time changes in probe orientation angles.
As with the head pressure sensor, the size, grid, design, and sensor quantity in the supplemental shaft pressure sensor array may very. In the most basic configuration, the shaft pressure sensor array comprises a single linear pressure array. Better functionality can be achieved by using two or preferably three linear pressure sensor arrays, especially when they are equally spaced about the outside of the shaft of the probe. In the most preferred configuration, the shaft pressure sensor array has a pressure sensitive area all the way around the probe shaft sized to be about 40 mm long and include over 100 individual pressure sensors. A shaft diameter may vary too, but preferably the shaft diameter is about 12.5 mm. Each individual pressure sensor may be a piezoelectric, resistive, or quantum tunneling composite pressure transducer, but in the preferred embodiment it is a capacitive transducer.
FIG. 4 is a diagram of an orientation tracking sensor means used in the preferred embodiment of the present invention. The orientation tracking means includes a three-axis magnetic sensor 25 with orthogonal sensitivity axes Mx, My, Mz, and a two-axis acceleration sensor 26 having sensitivity axes Ax, Ay accordingly. Importantly, Ax-axis is parallel to the Mx-axis and Ay-axis is parallel to the My-axis. Both the magnetic sensor 25 and the acceleration sensor 26 are mounted on a platform 41 so that X and Y axes are parallel thereto, which in turn is parallel to the probe head pressure sensing surface. Preferably, platform 41 is incorporated inside the probe handle to be in the vicinity of the sphincter during prostate examination. Magnetic sensor readings give sensor orientation relative to Earth\'s magnetic field. To compensate the magnetic sensor reading for a platform tilt relative to a horizontal plane, which is perpendicular to Earth\'s gravity vector, it is necessary to know the platform tilt angles. The two-dimensional accelerometer sensor is used here as a tilt sensor to provide elevation (φ) and rotation (θ) readings. The X, Y, Z magnetic readings can be traced back to the horizontal plane by applying the rotational equations shown below:
where Xh and Yh are Earth\'s magnetic vector projections to the horizontal plane. Once Xh and Yh are known, it is possible to calculate an azimuth angle as: