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PubMed2006

Effect of temporal subtraction technique on interpretation time and diagnostic accuracy of chest radiography.

OBJECTIVE: Our purpose was to compare reviewing time and diagnostic accuracy in the interpretation of radiographs without and with subtraction images and to examine whether this temporal subtraction technique can contribute to improving radiologists' performance. MATERIALS AND METHODS: Thirty cases with newly developed chest abnormalities on chest radiographs and 90 negative cases were selected. All chest radiographs were obtained with a computed radiography system. For the 90 negative cases, subtraction images were classified into two groups: 33 clean images without misregistration artifacts and 57 images with some misregistration artifacts. Eight radiologists (four board-certified radiologists and four radiology residents) participated in observer tests and interpreted the original radiographs without and with subtraction images using an independent test method. The reviewing time for each radiologist was recorded in each case. The observers' performance was evaluated by use of receiver operating characteristic (ROC) analysis. RESULTS: When subtraction images were available, the mean reviewing time per case was reduced significantly from 13.6 to 10.8 seconds for the cases with newly developed abnormalities (p < 0.001) and from 29.8 to 14.1 seconds for negative cases (p < 0.001). The reduction in the mean reviewing time with subtraction images was greater for clean images than for images with artifacts (17.7 vs 14.5 seconds, p < 0.001). The average mean area under the ROC curve value increased significantly from 0.942 without subtraction images to 0.988 with subtraction images (p = 0.025). There were significant differences in the sensitivity (0.963 with and 0.888 without the subtraction images) and the specificity (0.976 with and 0.899 without the subtraction images) (p < 0.001). CONCLUSION: The temporal subtraction technique can reduce reviewing time and also improve diagnostic accuracy in the interpretation of chest radiographs.

Etidronic Acid↗
PubMed2004

[ROC analysis of detection of interval changes in interstitial lung diseases on digital chest radiographs using the temporal subtraction technique].

PURPOSE: To demonstrate the clinical usefulness of a temporal subtraction technique for the detection of interval changes in various interstitial lung diseases on digital chest radiographs. MATERIALS AND METHODS: One hundred pairs of chest radiographs in 34 patients (63 with and 37 without interval changes) with various interstitial lung diseases were selected. All cases were confirmed by serial chest computed tomography (CT) and ascertained by radiologists. All chest radiographs were obtained with a computed radiography (CR) system, and temporal subtraction images were produced with an iterative image-warping technique. Four radiologists and two thoracic physicians provided confidence levels for interval changes in interstitial lung diseases with and without temporal subtraction. Their performances with and without temporal subtraction were evaluated by means of receiver operating characteristic (ROC) analysis using a sequential test. RESULTS: The area under the ROC curve (Az) values of six observers obtained with and without temporal subtraction were 0.90 and 0.78, respectively. Results showed that the detection of interval changes in interstitial lung diseases was significantly improved by the use of temporal subtraction images compared with CR images alone(P = 0.002). Furthermore, the high detection rate was achieved with temporal subtraction images regardless of the subtlety and location of interval changes. CONCLUSION: Temporal subtraction improved the diagnostic accuracy of radiologists in detecting interval changes in interstitial lung diseases on chest radiographs. It was also useful for cases of multiple interval changes.

Adult↗
PubMed1981

Dual energy film subtraction technique for detecting calcification in solitary pulmonary nodules.

A simple film subtraction technique has been devised that isolates calcium image contrast and mutes tissue image contrast. Two exposures are required. The first is made on XL film using a 65 kVp beam filtered with 2 mm aluminum. The second is made on OG (high contrast) film using a 130 kVp beam filtered with 2 mm copper and 2 mm aluminum. The effective energies of these two beams are approximately 45 keV and 83 keV, respectively. A subtraction image is made, using the low energy image for the mask. With this technique it is possible to detect concentrations of 125 mg/cm3 of diffuse calcification in a chest nodule 1 cm in diameter. If the presence of diffuse calcification is found to be an indicator of benignancy in solitary pulmonary nodules, this technique may have diagnostic value for the detection of such calcification. Computerized tomographic findings are discussed and related to this technique.

Calcinosis↗
PubMed2003

[Detection of acute cerebral infarction by dual echo subtraction technique in MR imaging].

The purpose of this study was to develop an image enhancement technique to detect acute cerebral infarct regions in brain MR images. Transverse relaxation times for abnormal changes tend to be longer than those for normal tissues. In order to obtain MR images with two different echo times, we employed the fast spin echo sequence. We then employed the image subtraction technique using two T(2)-weighted images to enhance acute cerebral infarct regions. As a result, the areas of acute cerebral infarct regions were enhanced as regions of higher signal than normal regions of brain tissue. Further, high signal areas in dual echo subtraction images corresponded to cerebral infarct regions of high signal areas in diffusion weighted images (DWI). We found that the image subtraction technique is useful to enhance very subtle regions of acute cerebral infarction in MR images. Because we employ the difference between transverse relaxation times for normal and abnormal tissues, which does not depend on the strength of the magnetic field, the dual echo subtraction method can be used in many hospitals.

Aged↗
PubMed1984

Intravenous left ventriculography utilizing digital subtraction technique.

To detect the left ventricular boundary in the intravenous ventriculography, we used a subtraction technique for background suppression. Images containing contrast medium and reference mask images were transferred to a computer through a flying spot scanner and stored on the digital disc. Stored reference mask images were subtracted from the digitized contrast images. The resulting images were then electronically enhanced to extract the left ventricular (LV) image. The LV boundary was delineated with an algorithm we have developed and the volume of the LV cavity was calculated automatically. The validity of this method was compared with data obtained from conventional left ventriculogram (LVG). In 11 patients, values for end-diastolic volume (EDV), end-systolic volume (ESV) and ejection fraction (EF) calculated from the intravenous LVG were correlated closely with those from the conventional LVG (128 +/- 38 (SD) vs 133 +/- 39 ml, r = 0.95; 50 +/- 28 vs 53 +/- 30 ml, r = 0.98; 63 +/- 10 vs 62 +/- 12%, r = 0.96, respectively). Nine patients with valvular regurgitation were followed up serially after valve replacement. EDV index fell significantly after corrective surgery (145 +/- 50 to 81 +/- 33 ml/m2, p less than 0.02), whereas, EF was affected variably depending upon the preoperative state (58 +/- 13 to 61 +/- 11%, not significant). Thus, this method is less invasive than conventional LVG and has successfully allowed for sequential determination of ventricular function on an outpatient basis.

Adult↗
PubMed1991

Rapid determination of cancellous bone mineral loss in ovariectomized rats by a subtraction technique.

We present a rapid technique for determining cancellous bone mineral changes in small experimental animals. We used the distal centimeter of the right femur from ovariectomized (OX) (N = 30) and shamovariectomized (ShOX) (N = 28) rats, aged 90 days at surgery and killed at times from 125-540 days postsurgery. We used dual photon absorptiometry to scan the segment three times: intact, after parasagittal splitting, and after removing all cancellous bone. We equated the difference between the second and third scans to cancellous bone mineral content (Cn.BMC). To validate this, we compared it with histomorphometrically determined bone volume (BV/TV) of the proximal tibial metaphysis of the same rat. Parasagittally splitting the segment removed no detectable mineral. OX rats had 40% less Cn.BMC than ShOX rats. However, OX rats had 80% lower BV/TV than ShOX rats. The subtraction technique not only makes a rapid, reasonable assessment of cancellous bone loss in OX rats but permits a smaller sample size than histomorphometry. The histomorphometric technique finds a greater difference between OX and ShOX rats because it examines a region where cancellous bone loss is more marked than does the scanning technique. The current technique measures bone of not only the central secondary spongiosa but also the juxtacortical region and the primary spongiosa, where OX-related differences are less prominent. The principles of this subtraction technique proved workable. However, for the future, we recommend a two-scan technique using a dual energy X-ray scanner. It is likely to take only 20-30 min per specimen to assess cancellous bone mineral.

Absorptiometry, Photon↗
PubMed1991

[Further possibilities for the application of the digital subtraction technique in neuroradiologic diagnosis].

The article presents, as methods that can be used in addition to digital subtraction angiography, ventriculography, myelography, discography as well as control examinations of shunts and port systems to widen the scope of digital subtraction techniques (DST) in neuroradiological diagnostics. Besides the reduction of amount and concentration of contrast media, more comprehensive and better diagnostic results were achieved for all examination methods with regard to the functional and dynamic aspects, the spatial resolution being of comparable quality.

Anastomosis, Surgical↗
PubMed2006

Development of a novel digital subtraction technique for detecting subtle changes in jawbone density.

The objective of this paper is to develop a novel digital subtraction technique for serial intra-oral radiography, which would allow the detection of subtle variations in grey values. Digital images of the maxilla of a dried human skull and of a fresh pig mandible were acquired using intra-oral photostimulable phosphor plates (Digora FMX, Soredex, Helsinki) with an aluminium calibration stepwedge incorporated in the filmholder. Exposures were made with an X-ray tube for intra-oral radiography (Prostyle Intra, Planmeca, Helsinki). During pilot testing, parameter settings were adapted to reach an optimal contrast. Exposures were repeated within a 1-week interval to determine the test-retest reliability of the development. After in vitro and in vivo testing, the exposure technique and software development were used to evaluate its applicability in a pilot clinical case. Although parameter settings remained stable during the in vitro studies, the clinical exposures yielded non-linear digital images, thus, not readily suitable for data acquisition and comparison of the regions of interest. To allow further analysis, image processing was carried out using self-developed software for semi-automated linearisation and optimised contrast normalisation. This processing significantly increased the precise quantisation of jawbone density and the assessment of subtle bone density changes in arbitrarily selected regions of interest of in vivo exposures. The clinical applicability of the technique is demonstrated in a pilot case. It was demonstrated that minute densitometric deviations could be detected. The present technique and image processing may allow the quantification of jawbone density.

Animals↗
PubMed1982

Intravenous arteriography using digital subtraction techniques.

The application of digital computers to electronic x-ray imaging devices has rejuvenated interest in the field of intravenous arteriography. By utilizing computer image subtraction techniques, digital roentgenographic systems based on fluoroscopy or computed tomography (scanned projection radiography) provide significantly improved vascular imaging compared with conventional film subtraction methods. Digital subtraction angiography schemes isolate contrast media in the vessel by detecting differences in images obtained before and after the injection of contrast medium or changes in the relative attenuation of contrast media at different x-ray energies. Present applications include carotid and peripheral arteriography, thoracic and abdominal aortography, pulmonary arteriography, and ventriculography. Future applications may include intracerebral and coronary arteriography. These systems should provide low-risk outpatient screening arteriography.

Angiography↗
PubMed1983

Diagnosis of upper-abdominal infections by In-111 labeled leukocytes with Tc-99m colloid subtraction technique.

In 65 patients suspected of upper-abdominal inflammatory disease, indium-111 leukocyte scintigraphy was combined with a Tc-99m(Sn)colloid scan by computer-assisted subtraction. In 84% of these cases, a definite diagnosis would not have been possible without this method of subtraction. Accuracy was found to be 80%, sensitivity 93%, and specificity 59%. False-positive results were due either to noninfectious inflammatory lesions with accumulation of leukocytes or to some pitfalls in the subtraction technique itself.

Abdomen↗
PubMed1990

Subtraction technique for contrast-enhanced MR images of musculoskeletal tumors.

Vascularized malignant tissue, fat and hemorrhage may have similar intensities on Gd-DTPA-enhanced, T1-weighted MRI performed to evaluate musculoskeletal tumors. We describe a simple, rapid post-processing subtraction technique which resulted in improved definition of these tissues in 33 of 42 examinations. While the subtraction process is susceptible to complex patient motion, the improved contrast can be obtained without modifying standard pulse sequences.

Bone Neoplasms↗
PubMed2006

A computer-aided temporal and dynamic subtraction technique of the liver for detection of small hepatocellular carcinomas on abdominal CT images.

It is often difficult for radiologists to identify small hepatocellular carcinomas (HCCs) due to insufficient contrast enhancement. Therefore, we have developed a new computer-aided temporal and dynamic subtraction technique to enhance small HCCs, after automatically selecting images set at the same anatomical position from the present (non-enhanced and arterial-phase CT images) and previous images. The present study was performed with CT images from 14 subjects. First, we used template-matching based on similarities in liver shape between the present (non-enhanced and arterial-phase CT images) and previous arterial-phase CT images at the same position. Temporal subtraction images were then obtained by subtraction of the previous image from the present image taken at the same position of the liver. Dynamic subtraction images were also obtained by subtraction of non-enhanced CT images from arterial-phase CT images taken at the same position of the liver. Twenty-one of 22 nodules (95.5%) with contrast enhancement were visualized in temporal and dynamic subtraction images. Compared with present arterial-phase CT images, increases of 150% and 140% in nodule-to-liver contrast were observed on dynamic and temporal subtraction images, respectively. These subtraction images may be useful as reference images in the detection of small moderately differentiated HCCs.

Aged↗
PubMed1993

Magnetic resonance imaging of blood flow with a phase subtraction technique. In vitro and in vivo validation.

RATIONALE AND OBJECTIVES: One promising approach to flow quantification uses the velocity-dependent phase change of moving protons. A velocity-encoding phase subtraction technique was used to measure the velocity and flow rate of fluid flow in a phantom and blood flow in volunteers. METHODS: In a model, the authors measured constant flow velocities from 0.1 to 270.0 cm/second with an accuracy (95% confidence intervals) of +/- 12.5 cm/second. There was a linear relationship between the magnetic resonance imaging (MRI) measurement and the actual value (r2 = .99; P = .0001). RESULTS: Measuring mean pulsatile flow from 125 to 1,900 mL/minute, the accuracy of the MRI pulsatile flow measurements (95% confidence intervals) was +/- 70 mL/minute. There was a linear relationship between the MRI pulsatile flow measurement and the actual value (r2 = .99; P = .0001). In 10 normal volunteers, the authors tested the technique in vivo, quantitating flow rates in the pulmonary artery and the aorta. The average difference between the two measurements was 5%. In vivo carotid flow waveforms obtained with MRI agreed well with the shape of corresponding ultrasound Doppler waveforms. CONCLUSIONS: Velocity-encoding phase subtraction MRI bears potential clinical use for the evaluation of blood flow. Potential applications would be in the determination of arterial blood flow to parenchymal organs, the detection and quantification of intra- and extra-cardiac shunts, and the rapid determination of cardiac output and stroke volume.

Adult↗
PubMed1983

A digital subtraction technique for dental radiography.

The relative accessibility and stability of the teeth facilitate generation of geometrically identical radiographs over a period of time. When such radiographs are digitized with the aid of a TV camera coupled to an analog to digital converter and a computer, it is possible to conveniently produce subtraction images of high diagnostic value. A digital subtraction technique for longitudinal dental radiography is described; this technique should be applicable to diagnostic situations characterized by a need to detect small changes occurring over a period of time in areas where substantial amounts of structured noise limit their detectability.

Computers↗
PubMed1999

Diagnostic value of sialography with both the conventional and digital subtraction techniques in children with primary and secondary Sjögren's syndrome.

OBJECTIVE: The application of anamnestic data on siccative symptoms required for classifying adult Sjögren's syndrome is limited in childhood. Instrumental test procedures are therefore necessary for objectively recording the oral and ophthalmologic manifestations of the disease. The aim of this study was to clarify the sialographic changes that occur in Sjögren's syndrome in children. STUDY DESIGN: A total of 23 sialograms were obtained with both conventional and digital subtraction techniques in 21 children with primary (10 girls and 1 boy) or secondary Sjögren's syndrome (10 girls). The films were assessed by 3 physicians and submitted for a consensus analysis if necessary. RESULTS: The pathologic features observed in the children varied from a slightly narrowed ductal system to multiple peripheral ductal ectasias and completely destroyed parenchyma. Sialographic examinations demonstrate that, with progressing disease, regression of acinar dilatations and rarification of the ductal system occur. CONCLUSION: The results show that the spectrum of sialographically recordable lesions in Sjögren's syndrome in children is greater than is described thus far in the literature.

Adolescent↗
PubMed2002

A dual-energy subtraction technique for microcalcification imaging in digital mammography--a signal-to-noise analysis.

Breast cancer may manifest as microcalcifications (microCs) in x-ray mammography. However, the detection and visualization of microCs are often obscured by the overlapping tissue structures. The dual-energy subtraction imaging technique offers an alternative approach for imaging and visualizing microCs. With this technique, separate high- and low-energy images are acquired and their differences are used to "cancel" out the background tissue structures. However, the subtraction process could increase the statistical noise level relative to the calcification contrast. Therefore, a key issue with the dual-energy subtraction imaging technique is to weigh the benefit of removing the cluttered background tissue structure over the drawback of reduced signal-to-noise ratio in the subtracted microC images. In this report, a theoretical framework for calculating the (quantum) noise in the subtraction images is developed and the numerical computations are described. We estimate the noise levels in the dual-energy subtraction signals under various imaging conditions, including the x-ray spectra, microC size, tissue composition, and breast thickness. The selection of imaging parameters is optimized to evaluate the feasibility of using a dual-energy subtraction technique for the improved detection and visualization of microCs. We present the results and discuss its dependence on imaging parameters.

Breast↗
PubMed1990

Improved subtraction technique in intravenous digital left ventriculography: comparison with radionuclide studies.

Adequate processing of left ventricular angiograms depends on the visualisation of all segments of the ventricular wall. At the same time, subtraction of different images can enhance different heart segments but commercially available methods do not allow simultaneous viewing of several images masked by different processes. Using our software, for each studied frame, a four quadrant display permits the simultaneous visualisation of a mask mode image, a diastolic-systolic difference image, an image obtained by subtraction of a frame at the same cycle time and a composite mask subtracted image. The composite mask image is obtained by weighting three images according to videodensitometric measurements by reference to previously acquired data. This method facilitates contour delineation and computation of the ejection fraction by area-length method. Correlation with radionuclide estimates of left ventricular ejection fraction is higher (n = 60, r = 0.90, SEE = 8%) than using the classical mask mode display (n = 60, r = 0.82, SEE = 11%). In a subgroup of 30 patients the contrast medium was injected in an antecubital vein and the correlation coefficient remained satisfactory (n = 30, r = 0.89, SEE = 7%) when compared with the classical subtraction technique (n = 30, r = 0.70, SEE = 12%). We therefore conclude that the composite mask method gives comparatively similar values for left ventricular ejection fraction to those acquired by radionuclide angiography.

Angiography, Digital Subtraction↗