1. IntroductionRealtime smoothed mask-digitalsubtraction (RSM-DSA) method byShimadzu digital spot imaging sys-tem DIGITEX PRO (DAR-3000)was developed for angiography. Thisimaging method discerns the differ-ence in frequency components. 1) 2) 3)

This report relates practical expe-riences that we have gained fromapplying this imaging method to adouble-contrast esophagography.As the application in this case is anon-vascular examination, we havenamed this method "RealtimeSmoothed Mask-Digital Subtrac-tion Radiography" (RSM-DSR).

2. RSM-DSR Principles Conventional angiography subtrac-tion relies on time-interval differ-ence to obtain target images. Incontrast, RSM-DSR is a subtrac-tion method that discerns the dif-ference in frequency components ofimages. The frequency distributionin an esophagraphy comprises bothlow and high frequency domains.The low frequency domain typical-ly has gradual density changes.The domain is made up of bone,soft tissue and air. On the otherhand, the high frequency domainhas sharp density changes. In thecase of a barium-filled esophagus,

99 IINNNNOOVVAATTIIOONN

Development in

Medical

Applications

Practical Experience in UsingDIGITEX PRO (DAR-3000) forDouble-contrast Esophagography

1100IINNNNOOVVAATTIIOONN

Fig. 2 Optimum conditions forRSM-DSRThe image at the left end is thelive image and the four images tothe right have all had the low-frequency components removedusing the high pass filterprocess. Desired information forthe two images on the right endis lost due to excessivesubtraction. Approximately0.1Lp/mm is judged to be thebest subtraction frequency forremoving low-frequencycomponents.

Live Image

Subtracted low frequency: 0.1Lp/mmI.I. internal electrode voltage: 480V

High Pass Filter Process Image

Fig. 1 RSM-DSR principlesThe right end RSM-DSR image isobtained by subtracting the fuzzy-mask image from left live image. Liveimage is acquired in a mere 33msecafter acquiring fuzzy-mask.

Live Image Fuzzy-mask Image RSM-DSR

Fig. 3 Normal esophagusThe image on the left is the live imageand the one on the right is the RSM-DSR.

1111 IINNNNOOVVAATTIIOONN

the high frequency domain is com-posed of the contrast medium andthe border areas of esophagealmucosa, bone and soft tissue. With RSM-DSR, the low-frequencydomain from an image containinghigh and low frequency domain issubtracted to leave an image withjust the high-frequency domain.The subtracted low-frequencyimage is known as a fuzzy-maskimage and is created by adjustingthe internal electrode voltage ofthe image intensifier (I.I.). TheRSM-DSR is obtained through arealtime subtraction process ofthis fuzzy mask image from thefocused live image. Fig 1. showsthe actual image processing.The I.I. internal electrode voltageswitches instantaneously in syncwith X-ray radiation to enableacquisition of a live image in just33msec after the fuzzy-mask imagehas been captured, which meansthat motion artifact due to breath-ing and body movement does noteffect the image even if subtractionprocessing is performed. Conse-quently, continuous acquisitionenables cine observation of RSM-DSR esophagus images. Further-more, RSM-DSR allows image acqui-sition and moving of the I.I to trackthe barium flow at the same time.

3. EquipmentThe devices used were a remoteR/F table and a DIGITEX PRO(DAR-3000) digital spot imagingsystem, which are products manu-factured by Shimadzu Corporation.The image acquisition modes avail-able are digital spot, serial imagingand various type real-time DSA.The maximum acquisition framerate is 7.5 frames per second. Allimaging modes have 1024 x 1024matrix spatial resolution and 12-bit(4096 gradation) density resolu-tion. The RSM-DSR technique usesan RSM-DSA function that is oneapplication of DSA imaging. The I.I.has multiple field sizes of 12, 9 and7 inch; the 9-inch field size wasused in all the imaging describedin this report.

Fig. 4 sm2 superficial cancerThe image on the left is the live image and the one on theright is the RSM-DSR. The arrows show that intra-epithelialevolution has gone as far as blocking the ligament.

Fig. 5 Type 3 progressive cancerThe image on the left is the live image and the one on theright is the RSM-DSR. The RSM-DSR is clearly superior as itprovides uniformity of density.

1122IINNNNOOVVAATTIIOONN

4. Optimum ConditionSettings

First, an image was created using ahigh pass filter process to removeany low-frequency components inorder to set the optimum condi-tions (I.I. internal electrode voltage)for obtaining the appropriate fuzzy-mask image (Fig. 2). Taking intoconsideration factors such as pres-ence of artifact and asperity inlesion areas that occur in the outervicinity of border areas of theesophagus, it was judged thatapproximately 0.1Lp/mm of the lowfrequency components could beremoved. Moreover, the optimuminternal electrode voltage for thiswas 480V, so this was set as theoptimum condition for RSM-DSRin esophagraphy.

5. Visual Evaluation ofImage Quality

Four radiologists visually evaluat-ed the image quality of RSM-DSRand live images in turn. The para-meters that were investigated werethe density uniformity of thewhole esophageal mucosa and theexistence, distribution and surfacestructure of lesions in the case ofesophageal cancer in both normaland abnormal cases. Fig. 3 shows anormal esophagus. Uniformity ofdensity of upper parts of the esoph-agus that overlaid with the lung,and lower parts of the esophagusthat overlaid with the heart andblood vessels is clearly superior inthe case of RSM-DSR. Fig. 4 showsan abnormal case of 0-IIc typesuperficial carcinoma at the sm2depth of invasion. With regard tothe distribution and surfaceappearance of the main lesionsexisting in the Mt region, the RSM-DSR is equal if not slightly superi-or to the live image.The RSM-DSR produces a clearerimage of the interrupted mucosalfolds due to intraepithelial exten-tion at the oral or anal side. Cineobservation of this on a monitorafter the examination enabled deci-

sive diagnosis. Fig. 5 shows anabnormal case of type 3 advancedcarcinoma. The RSM-DSR image isclearly more superior in showingthe uniformity of density of the areawhere the oral side of the esophagusis overlaid by the lung. It is evidentthat the RSM-DSR also would iden-tify with greater ease other lesionsthat might occur in this overlaidarea. Barium often accumulates inthe presence of advanced carcinoma,which hinders good illustrationwith conventional imaging tech-nique (ie. non-RSM-DSR technique).But clear depiction of lesions inadvanced carcinoma is possibleusing the RSM-DSR that producesclean double-contrast images.

6. DiscussionWe were able to observe and selectimages on screen at any time direct-ly after completion of imagingbecause we used the DIGITEX PRO(DAR-3000) - a digital spot imagingsystem manufactured by ShimadzuCorporation - that allows imagingat a top speed of 7.5 frames per sec-ond. For this reason, an increasedradiation from having to retake dueto bad timing in imaging is reduced.Notably, the DAR-3000 is extreme-ly useful in the imaging of theesophagus. Also, thanks to the capa-bility to subtract low-frequencycomponents, images can be depictedwith greater uniformity density forthe whole esophageal mucosa thanwith conventional digital imaging(live images). This suggests thatlocalized diagnosis capacity of otherlesions not noticed during examina-tion and depiction capacity of thesurface appearance of known lesionsand lesion distribution areimproved.However, in the case of live images- that are the source images - RSM-DSR is not effective when there isan abundance of or poor deposit ofbarium. In some cases, tube inser-tion or steps to provide correct pos-ture are required. In short, the radi-ologist still has to be extremelycareful in double contrast imaging.Application of RSM-DSR to the

field of esophagrams has been sug-gested as being useful and willmost likely contribute greatly toX-ray diagnosis of esophageal can-cer - in particular, superficial car-cinoma that requires collection ofmicroscopic mucosal information.Moreover, this imaging method canbe expected to have major practicalapplications in cancer diagnosisfrom now on because it can depictthe whole of the esophagus in oneimaging session.

7. Summary1) The optimum conditions forRSM-DSR in double-contrastesophagraphy were as follows: I.I.internal electrode voltage of 480V(subtraction frequency of approxi-mately 0.1 Lp/mm )2) RSM-DSR provided superiordepiction capacity beyond that oflive image in all of the examinationitems. Notably, the RSM-DSRdepiction of density uniformity andsurface appearance of lesions wassuperb.The above shows that RSM-DSRhas an excellent capacity fordepicting the esophagus in themediastinum that is composed ofmultiple different densities, whichsuggests that this method is usefulfor double-contrast esophagography.

Reference Contributions1) Ichiro Sakamoto, Masashi Urano, KokenMatsuo et al: DIGITEX 2400 Practical Expe-rience, MEDICAL NOW: 1995, 24: 12-152) Masumi Kawai, Shuji Tanaka, TakeshiShiomi et al: Realtime Smoothed Mask DSAMethod (RSM-DSA method) Development,Shimadzu Review separate volume: 1996,53 (2): 107-1163) Hiroshi Sawada, Hitoshi Kobayashi:About 3D-DSA Application "NaviDSA", MED-ICAL NOW: 1997, 33: 16-17

Contributed byAkihiro Ino, Kenji Kawamoto, KiyohisaHiraka, Makoto Ueda and Kouji MasudaDepartment of Clinical Radiology,Graduate School of Medical Sciences,Kyushu University