Digital Subtraction Imaging Research Articles

Atlas of Image-Guided Intervention in Regional Anesthesia and Pain Medicine.

Atlas of Image-Guided Intervention in Regional Anesthesia and Pain Medicine. By James P. Rathmell, M.D. Philadelphia, Lippincott Williams & Wilkins, 2006. Pages: 186. Price: $99.00.In an era whereby dozens of new pain texts, handbooks, and atlases seem to be published every year, one might wonder, “How can one book stand out in such a crowded field?” To answer this question, one need only open a newspaper to view the latest advertising section, or peer out the window at the nearest Wal-Mart. The answer, of course, is to combine quality and value with convenience.Owning a copy of Atlas of Image-Guided Intervention reminds me of the USO tours I used to go on when stationed in Europe, whereby one could see the 18 main attractions in Paris in one long, holiday weekend. While it’s by no means equivalent to spending a semester abroad, all of the major “attractions” are covered in less than 200 easy-to-read pages. There are other books that delve deeper into ongoing controversies in interventional pain management or offer more minutiae, but who has the time to sift through a 2,000-page textbook? For the nerve blocks covered in this book, almost all relevant information is covered in an alluring, easy-to-follow format.In fact, one of the sections we were most impressed by was the first one, which is rarely covered in any meaningful way in other atlases. In chapter 1, Dr. Rathmell explains the advantages and disadvantages of using various types of needles and provides excellent tips on how best to steer them. The next chapter, on radiation safety, which describes how to minimize radiation exposure and optimize image quality, is like a 6-h radiology course condensed into a half dozen pages. The diagram outlining the amount of radiation exposure during various fluoroscope and clinician positions is extremely informative and sure to prevent unnecessary radiation exposure. It should be posted on the wall of every fluoroscopy suite in academic teaching hospitals. The final two chapters in this section address the drugs we inject into patients, including contrast agents, local anesthetics, steroids, and neurolytic agents. We both thought these two chapters were among the top highlights of this book. The sections describing the differences between various contrast agents and depot steroids are detailed yet succinct, and the tables outlining the key points in both chapters are exceptional.Sections 2 and 3 cover the major spinal injection techniques and sympathetic nerve blocks, respectively. What we found most engaging in these sections were the figures demonstrating the ideal position of the fluoroscopy beam for each block and the geometric drawings showing the best angles for needle placement. The axial diagrams were appropriately detailed and easy to understand, as were the digital subtraction images in the selective nerve root block section. One of our favorite chapters in these sections was the one on celiac plexus block and neurolysis. In this chapter, the distinctions between the various approaches to the celiac axis are laid out elegantly, with the wide array of drawings and fluoroscopic and computed tomography images providing an excellent adjunct. Section 4 covers implantable drug delivery systems and spinal cord stimulation. Although brief, this section covers all the essential points as well as many clinical pearls that will greatly benefit interventional pain practitioners interested in neuromodulation.Whereas one of the most appealing qualities of this book is its conciseness, the flip side of this is that certain aspects must be shortened or omitted. Foremost, although the title contains the words regional anesthesia , the only commonly performed regional anesthesia technique covered was intercostal nerve block. We also thought the indication sections for some of the nerve block chapters could have been more detailed, and that some key complications were left out (e.g. , pneumothorax for thoracic facet blocks). The decision to include a rarely performed procedure such as intraarticular thoracic facet block but exclude cervical discography, which some surgeons request before every cervical fusion, is something we hope will be addressed in future editions of this book.If pain management books were cars, Atlas of Image-Guided Intervention in Regional Anesthesia and Pain Medicine would be the Chevrolet Corvette Z06: a well-designed, lightweight, performance-driven learning tool that’s easy to operate and turbocharged with hidden gold mines that can only be imparted by someone with extensive experience performing interventional pain management procedures. Overall, we think Atlas of Image-Guided Intervention in Regional Anesthesia and Pain Medicine is an outstanding book that will become a “must buy” for every pain management fellow and resident interested in pain medicine. In fact, we have already bought a copy for our own pain clinic.*Johns Hopkins School of Medicine, Baltimore, Maryland. scohen40@jhmi.edu

K-edge digital subtraction imaging with dichromatic x-ray sources: SNR and dose studies

The aim of the present work is to analytically evaluate the signal to noise ratio (SNR) and the delivered dose in K-edge digital subtraction imaging (KES) using two types of x-ray sources: a monochromatic x-ray source (available at synchrotron radiation facilities and considered as gold standard) and a quasi-monochromatic compact source. The energy separation ΔE between the two monochromatic beams is 1 keV and 4 keV for the two sources, respectively. The evaluation has been performed for both radiography and computed tomography. Different geometries have been studied to mimic clinical situations. In mammography, a pathology perfused by a contrast agent has been modelled; in angiography, a vessel superimposed to a ventricle or a stand-alone artery stenosis has been studied. The SNR and the skin dose have been calculated as a function of the detail diameter, the contrast agent (iodine and gadolinium), and its concentration in the tissues. Results show that for ΔE = 4 keV a slightly higher delivered dose is required to obtain the same SNR with respect to ΔE < 1 keV. A similar study has been performed for KES-CT. Computer simulations of CT images performed with Snark software are shown to validate the analytical calculations.

In vitro cleaning efficacy and resistance to insertion test of interdental brushes

The aim of this study was to compare the resistance to insertion forces and cleaning efficacy values of triangular interdental brushes (TIB) and conventional round interdental brushes (RIB). Extracted human teeth were fixed in a socket and matched to pairs simulating interdental spaces. Before and after standardized cleaning of the proximal surfaces, the pre- and postbrushing situations were registered with a digital camera. The cleaning efficacy was quantified by digital image subtraction. The forces necessary for insertion were measured with a load cell. The ratio between the relative cleaning efficacy and the forces necessary for insertion was calculated. The results of our study revealed that the relative cleaning efficacies of round and TIB were equal. There were no statistically significant differences. TIB showed significantly lower resistance to insertion values. Consequently, at identical resistance to insertion the TIB cleaned more effectively compared with the RIB, which means that the same effectiveness was reached by significantly lower forces at insertion. TIB showed a more favorable ratio between relative cleaning efficacy and resistance to insertion than RIB.

Comparison of hard tissue density changes around implants assessed in digitized conventional radiographs and subtraction images

The aim of this in vivo study was to compare peri-implant bone density assessed by the mean gray value of the histogram in digitized conventional radiographs and two digital subtraction images (DSI) methods: linear and logarithmic. Thirty-four patients were monitored by standardized periapical radiographs 1 week after surgery and 4 months later. The radiographs were digitized and manipulated by means of EMAGO software. Linear and logarithmic DSI were obtained, and a filter was added to the logarithmic image. Control and test regions were selected and the mean value of the gray level of the histogram of these selected areas was obtained. This process was carried out in the digitized conventional radiographs (DCR) and the two methods of DSI. After that, the images were divided into two groups, with and without bone loss, and statistical analysis was performed. The results indicate that differences between the jaws did not reach significance, in all the images and in the two groups with and without bone loss. Furthermore, there was no statistically significant difference between the radiographic density assessed in the DCR and the two methods of subtraction images. Monitoring of peri-implant bone density by the mean gray value of the histogram in a selected area can be assessed either by linear and logarithmic DSI or by DCR.

Comparison of peri-implant bone level assessment in digitized conventional radiographs and digital subtraction images

Radiographic assessment of marginal bone height is included in longitudinal control of osseointegrated implants. However, accurate and reproducible results are difficult to obtain. The aim of the present study was to examine the differences between linear measurements in digitized radiographs (DR) and digital subtraction images (DSI) around endosseous implants and the interobserver variability. The bone height around 30 implants in 22 patients was assessed by 5 observers. Standardized periapical radiographs were obtained just after the surgery and 4 months later. The radiographs were digitized and manipulated by means of EMAGO software, and linear and logarithmic DSIs were produced. Furthermore, the logarithmic subtraction was enhanced with the use of a filter. The observers had the DRs and three methods of subtraction to assess bone height. ANOVA statistical procedures were applied to analyse differences between the observers in the four assessed images and the Tukey test was used to evaluate the differences between the images. Comparison of the bone height assessments indicated significantly (P<0.05) higher values in the DR than the three methods of DSI. The observers also had a statistically significant variability in this assessment (P=0.00003). DSI demonstrated lower values of linear measurements of the bone height around endosseous implants, compared with DR. Interobserver variability should be considered when comparing values from follow-up studies.

ACCF/AHA/HRS/SCAI Clinical Competence Statement on Physician Knowledge to Optimize Patient Safety and Image Quality in Fluoroscopically Guided Invasive Cardiovascular Procedures

ACCF/AHA/HRS/SCAI Clinical Competence Statement on Physician Knowledge to Optimize Patient Safety and Image Quality in Fluoroscopically Guided Invasive Cardiovascular Procedures

Usefulness of digital subtraction imaging with Levovist in the diagnosis of hepatocellular carcinomas

To classify hepatocellular carcinoma (HCC) based on the findings of digital subtraction imaging (DSI) and to compare DSI against other diagnostic imaging modalities to assess its reliability DSI was performed in 68 patients with HCC (72 nodules) and the enhancement patterns of blood flow in the tumor were assessed during the early phase, the portal phase and the late phase. In addition, the findings obtained by DSI were compared with those obtained by helical CT, digital subtraction angiography (DSA), CO2 angiography and CT during arterial portography (CTAP). Of the 72 nodules, blood flow was detected in 64 (88.9%) by early-phase DSI, in 61 (84.7%) by helical CT, in 62 (86.1%) by DSA and in 67 (93.1%) by CO2 angiography. Early-phase DSI did not demonstrate hypervascular enhancement in 8 HCC nodules (16.7%). These included 5 nodules in which other diagnostic imaging modalities also failed to identify tumor blood vessels and 3 nodules located in deep regions 87.5 mm or more from the body surface. With regard to these 5 nodules (10.4%) in which tumor vessels were not visualized during the early phase, late-phase DSI demonstrated relatively poor enhancement compared with normal hepatic parenchyma. Such late-phase defects in tumor enhancement were observed in 69 nodules (95.8%). DSI demonstrated characteristic findings of HCC enhancement during the early phase, the portal phase and the late phase, permitting classification of HCC to be performed.

Automated Image-matching Technique for Comparative Diagnosis of the Liver on CT Examination

When interpreting enhanced computer tomography (CT) images of the upper abdomen, radiologists visually select a set of images of the same anatomical positions from two or more CT image series (i.e., non-enhanced and contrast-enhanced CT images at arterial and delayed phase) to depict and to characterize any abnormalities. The same process is also necessary to create subtraction images by computer. We have developed an automated image selection system using a template-matching technique that allows the recognition of image sets at the same anatomical position from two CT image series. Using the template-matching technique, we compared several anatomical structures in each CT image at the same anatomical position. As the position of the liver may shift according to respiratory movement, not only the shape of the liver but also the gallbladder and other prominent structures included in the CT images were compared to allow appropriate selection of a set of CT images. This novel technique was applied in 11 upper abdominal CT examinations. In CT images with a slice thickness of 7.0 or 7.5 mm, the percentage of image sets selected correctly by the automated procedure was 86.6+/-15.3% per case. In CT images with a slice thickness of 1.25 mm, the percentages of correct selection of image sets by the automated procedure were 79.4+/-12.4% (non-enhanced and arterial-phase CT images) and 86.4+/-10.1% (arterial- and delayed-phase CT images). This automated method is useful for assisting in interpreting CT images and in creating digital subtraction images.

K-edge digital subtraction imaging based on a dichromatic and compact x-ray source

This work proposes a compact dichromatic imaging system for the application of the K-edge digital subtraction technique based on a conventional x-ray tube and a monochromator system. A quasi-monochromatic x-ray beam at the energy of iodine K-edge is produced by Bragg diffraction on a mosaic crystal. Two thin adjacent beams with energies that bracket the K-edge discontinuity are obtained from the diffracted beam by means of a proper collimation system. They are then detected using an array of Si detectors. A home-made phantom is used to study the image quality as a function of iodine concentration. Signal and signal-to-noise ratio analysis has also been performed. The results are compared with theoretical expectations.

Morphological age-dependent development of the human carotid bifurcation

The unique morphology of the adult human carotid bifurcation and its sinus has been investigated extensively, but its long-term, age-dependent development has not. It is important fundamentally and clinically to understand the hemodynamics and developmental forces that play a role in remodeling of the carotid bifurcation and maturation of the sinus in association with brain maturation. This understanding can lead to better prognostication and therapy of carotid disease. We analyzed the change of sinus morphology and the angle of the carotid bifurcation in four postnatal developmental stages (Group I: 0–2 years, Group II: 3–9 years, Group III: 10–19 years, and Group IV: 20–36 years, respectively) using multiprojection digital subtraction angiograms and image post-processing techniques. The most significant findings are the substantial growth of the internal carotid artery (ICA) with age and the development of a carotid sinus at the root of the ICA during late adolescence. The bifurcation angle remains virtually unchanged from infancy to adulthood. However, the angle split between the ICA and external carotid artery (ECA) relative to the common carotid artery (CCA) undergoes significant changes. Initially, the ICA appears to emanate as a side branch. Later in life, to reduce hydraulic resistance in response to increased flow demand by the brain, the bifurcation is remodeled to a construct in which both daughter vessels are a skewed continuation of the parent artery. This study provides a new analysis method to examine the development of the human carotid bifurcation over the developmental years, despite the small and sparse database. A larger database will enable in the future a more extensive analysis such as gender or racial differences.

Measurement of thin film thickness by electronic speckle pattern interferometry

The surface profile of an Al thin film and its thickness have been observed by electronic speckle pattern interferometry (ESPI). The Michelson interferometer was used as our basic interferometric system to obtain interference fringes on a CCD camera. These interference fringes, arising from the path differences due to the surface contours of the thin film, were analyzed with three different techniques: fast Fourier transform (FFT), phase shifting, and digital image subtraction; and the results were compared with each other. We also derived a new formula for the image subtraction method, which is only valid in one-dimensional calculations. An unwrapping procedure was used to obtain a continuous phase in the FFT and phase shifting methods. Results on thickness measurements are presented and are found to be in good agreement with each other.

Preliminary tests of a prototype system for optical and radionuclide imaging in small animals

We have assembled a prototype system for multimodal (radionuclide and optical) in vivo planar imaging of small animals (mice) using single photon emission radiotracers (Tc-99m) and a fluorescent marker (hematoporphyrin). Preliminary tests of the separate (optical and radionuclide) prototype imaging systems are presented, aimed at assessing their features and at determining the experimental protocol for in vivo imaging. Tests were performed on anesthetized healthy or tumor bearing mice. The gamma radiation detector is a small area (11 /spl times/ 11 mm/sup 2/) hybrid pixel detector based on the Medipix1 ASIC readout technology (64 /spl times/ 64 square pixels of 170 /spl mu/m by side), bump-bonded to a 300 /spl mu/m thick silicon detector. High spatial resolution in radioimaging (in the order of 1 mm) is achieved in vivo with a pinhole tungsten collimator (0.35 mm diameter, 90/spl deg/ acceptance angle, field of view of over 20 mm at 10 mm source distance). A future setup will use the Medipix2 hybrid detector (256 /spl times/ 256 square pixels, 55 /spl mu/m by side) bump-bonded to a 1 mm thick CdTe pixel detector. The laser-induced in vivo fluorescence imaging system comprises a pulsed light source (Nd:YAG laser, /spl lambda/=532 nm, energy/pulse = 30 mJ, pulse width = 50 ps, repetition rate = 10 Hz) used to excite the fluorescence emission (600-760 nm) of injected hematoporphyrin compound, a low sensitivity CCD camera and a commercial image analysis system. Images of normal and tumor regions are acquired by using a cut-on filter (/spl lambda/>600 nm). Digital image subtraction then enhances the tumor contrast with respect to the background. The final experimental protocol, only partly implemented here, includes independent and then combined optical/radio imaging of control mice and of a solid tumoral area (human thyroid derived anaplastic carcinoma) after injection of the radiotracer and/or of the fluorophore. In this work, the accumulation of the radionuclide in selected organs and of the fluorophore in the tumor provides the signal contrast in the two imaging modalities. Fluorescence spectroscopy of excised tissue samples is also performed to help the interpretation of fluorescence images. Results of in vivo combined imaging on tumor in mice will be shown in a next paper.

In vivo magnetic resonance imaging of xylem vessel contents in woody lianas

ABSTRACTPrevious reports suggest that in some plant species the refilling of embolized xylem vessels can occur while negative pressure exists in the xylem. The aim of this experiment was to use non‐destructive nuclear magnetic resonance imaging (MRI) to study the dynamics of xylem cavitation and embolism repair in‐vivo. Serial 1H‐MRI was used to monitor the contents of xylem vessels in stems of two dicotyledonous (Actinidia deliciosa and Actinidia chinensis, kiwifruit) and one monocotyledonous (Ripogonum scandens, supplejack) species of woody liana. The configuration of the horizontal wide bore magnet and probe allowed the imaging of woody stems up to 20 mm in diameter. Tests using excised stems confirmed that the image resolution of 78 µm and digital image subtraction could be used to detect the emptying and refilling of individual vessels. Imaging was conducted on both intact plants and excised shoots connected to a water supply. In the case of Ripogonum the excised shoots were long enough to allow the distal end of the shoot, including all leaves, to be exposed to ambient conditions outside the building while the proximal end was inside the MRI magnet. In total, six stems were monitored for 240 h while the shoots were subjected to treatments that included light and dark periods, water stress followed by re‐watering, and the covering of all leaves to prevent transpiration. The sudden emptying of water‐filled vessels occurred frequently while xylem water potential was low (below −0.5 MPa for Actinidia, −1.0 MPa for Ripogonum), and less frequently after xylem water potential approached zero at the end of water‐stress treatments. No refilling of empty vessels was observed at any time in any of the species examined. It is concluded that embolism repair under negative pressure does not occur in the species examined here. Embolism repair may be more likely in species with narrower xylem vessels, but further experiments are required with other species before it can be concluded that repair during transpiration is a widespread phenomenon.

The usefulness of digital subtraction imaging with Levovist in the diagnosis of focal hepatic tumors

This study was designed to evaluate digital subtraction imaging (DSI) with Levovist in the diagnosis of hepatocellular carcinoma (HCC), metastatic hepatocellular carcinoma, and hepatic hemangioma. The subjects in this study were 70 patients with 76 nodules of hepatic tumors (48 nodules in 46 cases of hepatocellular carcinoma, 20 nodules in 16 cases of metastatic hepatocellular carcinoma, and 8 nodules in 8 cases of hepatic hemangioma). Contrast enhancement of tumors acquired in the early, portal, and late phases with DSI were compared to classify the tumors. DSI of HCC showed contrast enhancement of 40 nodules (82.2%). High contrast enhancement in the early phase, which was maintained in the portal phase, changed to images with no contrast enhancement with partial persistence of contrast enhancement in the late phase. DSI of metastatic hepatic carcinomas demonstrated contrast enhancement of tumor of 18 nodules (90%) to a high degree in the early and portal phases, which changed to images with no contrast enhancement in the late phases. DSI of hepatic hemangioma maintained high contrast enhancement on tumor margins of 5 nodules (62.5%) and on the entire tumor of 3 nodules (37.5%) in the early, portal, and late phases. DSI of hepatic tumors (hepatocellular carcinoma, metastatic hepatocellular carcinoma, and hepatic hemangioma) provided characteristic findings of contrast enhancement in the early, portal, and late phases, and contribute to differential diagnosis.

Diagnosis of hepatocellular carcinoma using digital subtraction imaging with the contrast agent, levovist: Comparison with helical CT, digital subtraction angiography, and US angiography

Digital subtraction imaging was compared to helical CT, DSA, and US angiography to assess its usefulness in the evaluation of vascularity in hepatocellular carcinoma (HCC). Digital subtraction imaging using Levovist as the contrast agent was performed in 41 patients with 43 nodules (22 men and 19 women, aged 50 to 83 years; mean age, 65 years; mean maximum tumor diameter, 27.8+/-17.1 mm). Digital subtraction imaging showed hypervascular enhancement in 39 of the 43 nodules (91%). Helical CT showed areas of high attenuation in 40 of the 43 nodules (93%), while DSA and US angiography showed positive enhancement in 38 and 43 of the 43 nodules (88% and 100%), respectively. Digital subtraction imaging is useful for evaluating vascularity in HCC when the tumor can be visualized with non-enhanced US angiography.

Grade of fine composite mineral particles by dual-energy X-ray radiography

Standard X-ray radiographs of a composite particle made up by two mineralogical species with different linear attenuation coefficients produce 2D attenuation images that do not allow differentiating between a thin high stopping power and a thick low stopping power-mineralogical inclusion. Dual-energy (DE) imaging—i.e., a pair of radiographs taken at different incident X-ray energy—followed by digital image subtraction allows transforming the log processed energy images into two thickness images. This linear transformation permits the estimation of the particle volumetric content in the two phases and it is fast, as required for the development of an online ‘mineral liberation’ or a ‘washability’ sensor or a ‘valuable-phase-inclusion’ detector. In this paper, micro-CT was used to reconstruct fine particle slices so that the thickness of the two phases could be precisely calculated and compared with that one derived by DE. Preliminary experiments with monochromatic X-ray demonstrated the potential of the DE method to retrieve the particle grade. The tests were conducted with fine composite particles made up of two mineralogical species. Due to the nonhomogeneous composition and density variation within the two mineralogical phases segmented and also to partial volume effects in the tomographic reconstruction of particle slices, each of the two segmented phases have a Gaussian distribution of the linear attenuation coefficient μ (rather that one single value) and values of the σ( μ) such that the density distribution right tail of the species with the lower μ overlaps the left tail of the other species giving rise to a bimodal distribution of μ within the particle. This material feature adds further complexity to the problem.

The changing paradigm for the treatment of colonic hemorrhage: superselective angiographic embolization.

Colonic bleeding has historically been controlled by the use of localization procedures and surgery. Since our initial experience with superselective embolization of colonic bleeding, it has become our preferred method for the control of lower gastrointestinal hemorrhage. This follow-up study evaluates the Hartford Hospital experience using angiographic methods as the primary modality for the treatment of colonic bleeding. From March 1993 to September 1999, 27 patients who had angiographically visualized colonic hemorrhage underwent arterial embolization procedures. Diagnostic arteriography was performed in all patients using digital subtraction imaging and selective contrast injections into the superior and inferior mesenteric arteries. Once the bleeding site was identified, superselective arteriogram and embolization was performed. Platinum-fibered coils, Hilal coils, or polyvinyl alcohol particle emboli were then fluoroscopically guided into the bleeding vessel. A repeat arteriogram was performed to confirm occlusion and the absence of any collateral channels. All 27 patients were initially controlled with arterial embolization; 6 patients rebled (22.2 percent), and 5 of these patients required surgery. Two patients demonstrated ischemia (7.4 percent), one of which required surgical intervention. The other patient was followed up by colonoscopy. There was no mortality in this study. Superselective embolization is effective in controlling colonic hemorrhage and is associated with a low rate of postembolization ischemia. Our experience with angiography reinforces the paradigm shift from its use as a diagnostic tool to the primary method for the control of colonic bleeding. Because patients have been followed up for as long as seven years, this approach remains effective for the long-term treatment of colonic bleeding.

Modern Imaging in the Management of Cervical Carotid Stenosis

Most carotid artery disease is now imaged noninvasively given the availability of modern neuroimaging techniques. Concordance between noninvasive imaging modalities is sufficient in most cases to allow appropriate patient treatment. However, in the face of discordant noninvasive data where the degree of stenosis and presence of a complete occlusion are in question brachiocephalic angiography is employed. Additionally angiography allows for the morphological delineation of the stenosis, tandem lesions and extent of collateral circulation, and proximal lesions that may account for the patient's symptoms. In the hands of experienced operators using meticulous neuroangiographic techniques, modern catheters, and digital subtraction imaging techniques the risks of angiography are reduced, and the diagnostic or therapeutic benefit is enhanced. Angiography should be employed when lesion morphology is unclear due to discordant noninvasive data, clinical diagnosis is in question, or additional complicating factors are involved (i.e., associated intracranial aneurysms, tandem stenosis, symptomatic posterior circulation stenosis, and proximal origin stenosis of the brachiocephalic vessels).

A study on computer‐aided diagnosis based on temporal subtraction of sequential chest radiographs (in Japanese)

An automated digital image subtraction technique for use with pairs of temporally sequential chest radiographs has been developed to aid radiologists in the detection of interval changes. Automated image registration based on nonlinear geometric warping is performed prior to subtraction in order to deal with complicated radiographic misregistration. Processing includes global matching, to achieve rough registration between the entire lung fields in the two images, and local matching, based on a cross‐correlation method, to determine local shift values for a number of small regions. A proper warping of is determined by fitting two‐dimensional polynomials to the distributions of the shift values. One image is warped and then subtracted from the other. The resultant subtraction images were able to enhance the conspicuity of various types of interval changes. Improved global matching based on a weighted template matching method achieved robust registration even with photofluorographs taken in chest mass screening programs, which had previously presented us with a relatively large number of poor‐registration images. The new method was applied to 129 pairs of chest mass screening images, and offered registration accuracy as good as manual global matching. An observer test using 114 cases including 57 lung cancer cases presented better sensitivity and specificity on average compared to conventional comparison readings. In addition, newly developed image processing that eliminates the rib edge artifacts in subtraction images was applied to 26 images having pathological interval changes; results showed the potential for application to automated schemes for the detection of interval change patterns. With its capacity to improve the diagnostic accuracy of chest radiographs, the chest temporal subtraction technique promises to become an important element of computer‐aided diagnosis (CAD) systems.

Quantitative analysis of apical root resorption by means of digital subtraction radiography

Objective: This study was performed to assess the diagnostic and quantifying ability of digital subtraction images for simulated apical root resorption, as well as to compare the diagnostic accuracy of conventional intraoral radiographs with digital subtraction images for this condition. Study Design: Digital and intraoral radiographs of 10 sound maxillary central incisors and those with simulated apical root resorption were taken with varying horizontal and vertical angulations of the x-ray beam. Paired t tests were used to compare the lengths of the sound teeth on the images with their actual lengths, and the estimated amount of simulated apical root resorption was compared with the actual amount of tooth loss by means of Emago software. The diagnostic accuracy for detecting lesions was also evaluated on conventional intraoral radiographs and digital subtraction images through receiver operating characteristic (ROC) analysis. Results: There were no statistically significant differences between the actual lengths and those measured on the reconstructed images of the sound teeth. The calculated amounts of apical root resorption showed no statistically significant differences in comparison with the actual amounts (P > .05). The diagnostic accuracy of the conventional intraoral radiographs in detecting the lesions was low (ROC area = 0.6446). Conclusion: A quantitative analysis of small amounts of apical root resorption can be performed by means of digital subtraction radiography. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;91:369-73)