CA2234767A1

CA2234767A1 - Computed tomographic colonscopy

Info

Publication number: CA2234767A1
Application number: CA002234767A
Authority: CA
Inventors: Carl G. Coin
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-10-16
Filing date: 1995-10-16
Publication date: 1997-04-24
Also published as: EP0973433A4; EP0973433A1; AU4153996A; AU718433B2; WO1997014352A1

Abstract

A generally non-invasive method of colon examination in which the patient's colon is first inflated with gas, and then a plurality of cross-sectional images of the colon are taken by CT scanning along the longitudinal axis of the abdomen. Sets of data corresponding to each cross-sectional image are stored in computer memory. These sets of data are processed by a first computer program that reconstructs a three-dimensional model of the entire colon. Data corresponding to the reconstructed three-dimensional model of the colon are also stored in computer memory. A second computer program processes the original sets of data and the three-dimensional model data to reconstruct, for successive thin segments along the length of the entire colon, a crosssectional image for each segment which is perpendicular to the longitudinal axis of the colon lumen. These reconstructed images, which provide an exact simulation of the interior of the colon that would be viewed by means of colonoscopy, can be retrieved from memory and displayed for examination on a conventional video monitor, enabling the physician to detect any abnormalities of the colon wall anatomy which would tend to indicate the presence of an abnormality such as a polyp or tumor.

Description

CA 02234767 1998-04-1~

Description COM~ul~ TOMOGRAPHIC COLONSCOPY

~ACKGROUND OF THE lNv~N~l~loN

Field of the Invention The present invention relates to a safe and effective method for examining a colon which is generally non-invasive, substantially rapid, and which provides a continuous unobstructed view of the internal surface of the colon wall that facilitates detection and diagnosis of abnormalities in the colon anatomy.

~escri~tion of the Related Art There are presently two conventional methods utilized most often for examining the colon to detect abnormalities such as tumors or inflammatory proc~s~C in the anatomy of the colon. One stAn~A~d procedure is the colonoscopy, which consists of a direct endoscopic ~Y- in~tion of the colon with a flexible tubular structure known as a colonoscope which has fiber optic capabilities at one end thereof. The colonoscope is inserted through the patient's anus and directed along the length of the colon, thereby permitting direct ~n~oC~opic visualization of the colon polyps and tumors and in some cases, providing a capability for ~n~o-scopic biopsy and polyp removal. Although it does provide a precise means of colon ~Y- ;nAtion, colonoscopy is time-consuming, expensive to perform, and requires great care and skill by the ~YA ; n~, thorough patient preparation including purgatives and enemas, and ll~llAl ly a moderate anesthesia. Moreover, since colonoscopy is an ex~l -~ly invasive proc~ll~e, there is a significant risk of injury to the colon and the possibility of colon perforation and peritonitis, which can be fatal.
Another stAnAArd procedure for ~YA i n;ng the colon involves a "barium enema" followed by a fluoroscopic and radiographic ~YA~inAtion. In this pro~e~l~e, a solution of barium sulfite alone or mixed with air is first injected into the patient's colon by means of an enema, and then a fluoroscopic and radiographic eY- ;nAtion of the colon is performed. This eYA ;nAtion requires detailed observation by a radiologist, who must palpate the SUBSIIIUI~ SIEr a~UlE26) CA 02234767 1998-04-1~

patient's abdomen and repeatedly reposition the patient for the taking of a first set of x-rays. After these initial x-rays are completed, the patient evacuates the barium mixture and additional x-rays are taken. The total ~YA ;n~tion procedure can be of considerable duration, lasting from 20 minutes to 1-1/2 hours, and is very uncomfortable and ~e~-n~; ng both for the patient as well as the radiologist and x-ray technician. During the ~ ;n~tion, the patient may experience numerous difficulties such as problems retA;n;n~ the barium mixture, pain associated with palpation, and colon spasms. It is also possible for the colon to become impacted with barium, 1~A~; nq to severe constipation and interference with later diagnostics, thereby requiring the barium to be fully purged usin~ powerful and sometimes dangerous laxatives. This purging of the barium may also in rare inst~nce~ result in colon perforation with barium peritonitis, which is a lifetime debilitating and potentially fatal complication.
Because of the significant difficulties and potential complications involved with both of the conventional proce~ll~es for ~- ;n;ng the colon, there is still a need for a method of e~- ;n;ng a patient's colon which provides a precise and accurate visualization of the colon anatomy to detect abnormalities, is easy to conduct by medical personnel and generally non-invasive ~ ~ed with conventional pro~e~n~es, and which involves ;n; -1 ~;c~- fort to the patient.
~mary of the Invention The present invention is directed towards a generally non-invasive method of colon ~ ;n~tion in which the patient's colon is first inflated with gas, and then a plurality of cross-sectional images of the colon are taken preferably by CT sc~nn;ng along the longitl~;nAl axis of the AhAI -7 . A set of projection data obt~;n~ from the ~c~nn;ng and corresponding to each cross-sectional image is stored in c_ u~er memory. These sets of data are procecs~~ by a first ~ _ Ler ~loyl~m that reconstructs a three-~; -n~ional model of the entire colon. Data corresponding to the reconstructed three-~; -n~ional model of the colon are also stored in c~ ,-u~er memory. A s~co~ computer program processes the original sets of data and the three-~; ~n~ional model data to reconstruct, for successive thin se~_ ~nts along the length of the CA 02234767 1998-04-l~
W O 97/143~2 PCTnUS95/14634 entire colon, a cross-sectional image for each segment which is perpendicular to the longitll~; nA l axis of the colon lumen. These reconstructed cross-sectional images, which provide an exact simulation of the interior of the colon that would be viewed by means of colonoscopy, can be displayed on a video monitor and ~YA ; n~ to detect any abnormalities of the colon wall anatomy which would tend to indicate the presence of a tumor or inflammation.
It is an object of the present invention to provide an exL-~ ~ly accurate, relatively non-invasive method of ~- ;n;ng a colon in an uncollapsed state whereby cross-sectional images of sections of the colon which are perpendicular to the longitll~;nAl axis of the colon lumen can be viewed.
Another object of the present invention is to provide a method of ~YA ;n;ng a colon which ;n; ; zes the significant discomfort usually experienced by the patient during a conventional colon examination proce~llre.
A further object is to provide a method of ~YA ;n;ng a colon which is generally non-invasive so as to minimize any health risks associated with the eY~ ;nAtion p ~l..e.
Still another object of the present invention is to provide a method of eY~ ;n;ng a colon which requires ;n; -l patient preparation, can be completed in a substantially rapid period of time, and is relatively ;n~Yren~ive to perform.
Yet another object of the present invention is to provide a method of ~YA ining a colon which will promote freguent examination and early detection of conditions affecting the colon.

R~ief Descri~tion of the Drawinas The invention will be better understood after reA~;ng the following detailed description of the presently preferred ~; ~oA; ~nt thereof with reference to the appended drawings in which:
Figure 1 is a front perspective view of a colon.
Figures 2A through 2F illustrate a plurality of cross-sectional images pro~t~ce~ by the method of the present invention for the like-numbered segments indicated in Figure 1.
Figure 3 shows an exploded view of a portion of the colon with a cursor positioned adjacent a selected colon segment depicted in S~;l~lUltSIIt~l ~1PJIE26) CA 02234767 1998-04-lj cut-away to show the pre~nc~ of a polyp.
Figure 4 is a view taken along lines 4--4 of figure 3 of a cross-sectional image pro~llc~l by the method of the present invention for the colon s~_ ~nt adjacent the cursor in Figure 3.
Figures 5 and 5A-5F illustrate st~n~rd prior art cross-sectional images of the colon produced by CT sc~nn;ng.

Detailed Description of the Preferred Embodiment The method of the present invention requires initially that the patient's colon be filled with a gA~o~lC contrast agent, which preferably can be ambient air, cAr~o~ dioxide, xenon or nitrous oxide. If xenon or nitrous oxide is selected, a topical anesthetic effect will be pr~llc~. The gas is injected into the colon by means of a pump having an enema tip that is inserted into the patient's rectum. The purpose of inflating the colon is two-fold.
First, the colon normally sits within the A~l -n in a collapsed configuration, which does not permit accurate viewing of its true internAl structure. After being filled with gas, as shown in Figure 1, the colon ~ a defined shape which facilitates e~- ;n~tion of its internal wall surfaces. Second, the gas acts as a ~ollL~ast agent that is e~L-- -ly disting~li~hAhle from structures such as water, fat and t i ~r~ urrolln~ i ng the gas. It will be understood by those skilled in the art that the x-ray absorption values for gas, as designated in Hounsfield Units (8H.U.") along the Hounsfield Scale of x-ray absorption values, are at the extreme low end of the scale at approximately -1000 H.U., ~ ed to fat in the colon wall which has a value of about -100 H.U., water which has a value of 0, and bone, which is very dense and has a value of 1000 H.U. Gas therefore acts as an effective collLL~st agent when utilized in conjunction with transmission imaging of a body as by c~ ~Led tomographic ("CT") ~c~nning~
After the patient's colon has been inflated, ~ultiple cross-sectional images of the entire colon are taken along the longit~inAl axis of the patient's A~r~-_ ?n ~ preferably by CT scan employing helical scan imaging. Alternatively, a magnetic resonance imaging apparatus may be utilized to obtain the cross-sectional images. This CT sCAnni n~ prorltlces sets of projection data corresponding to st~n~Ard cross-sectional images of the colon taken generally along the longit~A;n~l axis of the abdomen, with CA 02234767 l998-04-l~

the sets of data being transmitted to ~uLer memory for storage therein. Representative illustrations of such cross-sectional images are shown in Figures 5A - 5F. It is known in the art to process these sets of projection data by computer to produce the 5 cross-sectional images shown in these Figures and labelled as prior J art, and to display such cross-sectional images on a conventional video monitor or to photograph the image by means of a ~. _uLer co~,Llolled camera. It will be appreciated, however, that although the prior art cross-sectional images that can be obtA; n~ from the 10 CT CcAnn;ng are of extremely high resolution, diagnosis of abnormalities in the colon anatomy from an e~A ;nAtion of such images may be hampered by the obliquity of projections resulting from the complex curvature of the colon within the abdomen.
After the CT scAnn;ng is completed, a first computer program 15 procesce~ the sets of projection data to reconstruct a three-~; ~n~ional model of the colon, as shown in Figure 1. Preferably, this reconstructed three-A; -ncional model will be a model of the gas-filled lumen of the colon. This first reconstruction p-~y~ -requires that an initial, representative prior art cross-sectional image of the colon ob~A;n~ by the CT ~çAnn;ng be displayed on a display means such as a high resolution video monitor. Next, a cursor is positioned on the lumen of the displayed prior art cross-sectional image through the use of input means such as a mouse or keyboard. In the preferred -- ~oA; -nt, the cursor comprises a small circle having a diameter preferably in the range of 5-20 millimeters. This outlined circle on the lumen of the displayed prior art cross-sectional image provides the starting point for this first p~y. , which operates to join together sections that are contiguous with the displayed prior art cross-sectional image and which are in the same range of x-ray absorption values as gas, to form a three-~; -ncional model of the colon. In the preferred ~ ~O~; -nt, the three-~; ~n~ional model will actually be a model of the gas-filled lumen of the colon. Following the execution of this first reconstruction program, data representing the re~oll~L~ucted three-~; -n~ional colon model are also stored in c~u~er memory.
After the three-~; -n~ional model of the colon has been reconstructed, a second computer program proc~s~- the initial sets of data and the three-~; -n~ional model data to reconstruct, for SI~IIIUIE SEEr ~E 26) CA 02234767 1998-04-l~
WO97/14352 PCT~US95/14634 cll~C~c~ive thin ce_ -nts along the length of the entire colon, cross-sectional images which provide a precise simulation of images of the interior of the colon along its length similar to that which would be viewed by colonoscopy. This second program functions by selecting contiguous thin colon segments along the length of the entire colon and reconstructing for each c~ nt the one cross-sectional view thereof which is perpendicular to the longit~;n~l axis of the colon lumen. In the preferred embodiment, the thiCkn~cc of these ~e_ ~nts will be selectively variable by the user and preferably will be in the range of 1-10 millimeters. In operation, this s~con~ program evaluates and processes the data stored in c~ uLer memory using the parameters of smallest cross-sectional diameter, area and circumference as applied to each ~e~_ Ant to reconstruct the one desired cross-sectional image for that s~_ ?nt which is perpendicular to the longit~l~;n~l axis of the colon lumen. Data representing each of the desired cross-sectional images is then stored in c; _ Ler memory, for ~ uent retrieval and viewing of the images. The program also preferably includes the capability to reconstruct the ~ e surrolln~;ng the periphery of the lumen of each cross-sectional image, at a tissue thi~kn~Sc that can be selectively varied by the user. In a preferred ~ ~o~; -nt, the resultant reconstructed images pro~llc~ by the second program, examples of which are shown in Figures 2A through 2F and which correspond to like- ~e~ed ~ nts in Figure 1, will enable a visualization of both the internal and the external wall ~urfaces for each cross-sectional image.
Once the ~econ~ program has been executed, the ~Y i n i ng physician can retrieve each reconstructed cross-sectional image indivi~~ ly from memory for display on the video monitor and if desired, for taking a photograph thereof. To do this, the physician displays the three-~i -ncional model of the colon on the monitor, positions the cursor adjacent the selected colon segment, as shown in Figure 3, and then uses the keyboard to input the appropriate display instruction to the ~ _~Ler, whereby the selected reconstructed cross-sectional image is displayed on the same monitor and replaces the view of the three-~i -n~ional model.
The user can return to the view of the three-~i e~cional model by inputting the appropriate instructions to the computer. ~he method of the present invention may also include the capability for CA 02234767 1998-04-l~
W O97/14352 PCTrUS95/14634 displaying the three-dimensional model with cursor on one monitor, while displaying the retrieved reconstructed cross-sectional images on another monitor. In addition, the program preferably allows the physician to view the reconstructed cross-sectional images in the con~eclltive sequential order of the sections along the length of the colon, generally in the ~nn~r of flipping through the pages of a book. It will be appreciated that the reconstructed images pro~l~e~ by the present invention provide a visualization of the colon as if it were a tube that had been straightened out and viewed from either end by multiple, co~c~ltive contiguous thin axial sections. This is because each reconstructed cross-sectional image is correctly angled in perpendicular relation to the longitl~in~l axis of the colon lumen. Using the method of the present invention to examine a colon, a physician will be able to readily detect polyps and tumors as small as 2 millimeters which intrude into the lumen of each cross-sectional image and which provide anatomic evidence of an abnormality in the colon. As shown in Figure 4, a polyp which intrudes into the colon lumen will be viewed as a roughly perpendicular protrusion to the internal colon wall and will show more precisely its true pathologic relation to the colon wall than would be shown by prior art images of the colon pro~llce~ by CT sc~nn; ng because such images are oblique and distorted. The reconstructed cross-sectional images pro~nce~ by the present invention can therefore assist the physician in dete~ ;n;ng the gross pathologic significance of a polyp or tumor.
Since many modifications, variations and changes in detail can be made to the described preferred~ ~o~; -nt of the invention, it is int~n~ that all matters in the foregoing description and shown in the acc~ _~nying drawings be interpreted as illustrative and not in a limiting sense. For example, it will be appreciated that the method of this invention may be carried out on other v;sco~
tissues within a body, such as arteries. Thus, the scope of the invention should be det~ ; n~ by the ~pp~n~ claims and their legal equivalents.

Claims

1. A method of imaging a colon to obtain a desired cross-sectional image of at least one substantially thin segment of the colon, which image is generally perpendicular to the longitudinal axis of the colon lumen, comprising the steps of:
(a) inflating the colon with gas:
(b) scanning the abdominal region by using scanner means to obtain initial sets of data representing a plurality of first cross-sectional images of the entire colon taken along the longitudinal axis of the abdomen;
(c) storing said initial sets of data in a memory;
(d) processing said initial sets of data to reconstruct a three-dimensional image of the colon;
(e) storing data representing said three-dimensional image in said memory;
(f) displaying said three-dimensional image on a display;
(g) using input means to select at least one substantially thin segment of said displayed three-dimensional image;
(h) processing said initial sets of data and said three-dimensional image data to calculate a reconstructed cross-sectional image for said at least one segment that is disposed in perpendicular relation to the longitudinal axis of the colon lumen;
and (i) storing data representing said reconstructed cross-sectional image in memory.

2. A method as recited in claim 1 wherein reconstructed cross-sectional images are calculated for additional contiguous substantially thin segments along the length of the entire colon.

3. A method as recited in claim 2 wherein said processing step of said initial data and said three-dimensional image data uses the parameters of smallest cross-sectional diameter, area and circumference as applied to said segments to calculate said reconstructed cross-sectional images.

4. A method as recited in claim 3 further comprising the steps of retrieving said data representing said reconstructed cross-sectional images from memory and displaying said reconstructed cross-sectional images on said display.

5. A method as recited in claim 3 wherein said selecting step comprises selecting segments each having a thickness in the range of 1-10 millimeters.

6. A method as recited in claim 1 wherein said scanning step is carried out with a computed tomographic scanner.

7. A method as recited in claim 1 wherein said scanning step is carried out with a magnetic resonance imaging apparatus.

8. A method as recited in claim 1 wherein said inflating step is carried out utilizing a pump apparatus having an enema tip which is inserted into the rectum.

9. A method as recited in claim 1 wherein said inflating step is carried out utilizing a gas selected from the group consisting of ambient air, carbon dioxide, nitrous oxide and xenon.

10. A method as recited in claim 4 further comprising the step of displaying said cross-sectional images on a display in a sequential order corresponding to the sequence of said segments along the length of said colon.

11. A method as recited in claim 1 wherein said processing step of said initial data comprises processing said initial sets of data to reconstruct a three-dimensional model of the gas-filled lumen of the colon.

12. A method of imaging a viscous tubular structure within a body to obtain a desired cross-sectional image of at least one substantially thin segment of said viscous tubular structure, which image is generally perpendicular to the longitudinal axis of the lumen of said viscous tubular structure, comprising the steps of:
(a) inflating said viscous tubular structure;
(b) scanning the body region wherein said viscous tubular structure is located by using scanning means to obtain initial sets of data representing a plurality of first cross-sectional images of said viscous tubular structure taken along the longitudinal axis of the bodily region;
(c) storing said initial sets of data in a memory;
(d) processing said initial sets of data to reconstruct a three-dimensional image of said viscous tubular structure;
(e) storing data representing said three-dimensional image in said memory;
(f) displaying said three-dimensional image on a display;

(g) using input means to select at least one substantially thin segment of said displayed three-dimensional image;
(h) processing said initial sets of data and said three-dimensional image data to calculate a reconstructed cross-sectional image for said at least one segment that is disposed in perpendicular relation to the longitudinal axis of the lumen of said viscous tubular structure; and (i) storing data representing said reconstructed cross-sectional image in memory.