Vascular tracing: a new videoangiographic algorithm.

Using a modified recursive video digital noise filter which was originally designed for commercial broadcast of noise reduced videotape, we have developed a digital processing algorithm for videoangiography. The vascular tracing algorithm traces out the entire route of a small, concentrated contrast bolus by literally "remembering" each minimum x-ray transmission (maximum contrast) seen by the video frame on a pixel by pixel basis over any amount of time recorded. High quality videoangiogram composite frames can be obtained and recorded. Large vascular segments are traced with small volumes. The additive nature of the vascular tracing image eliminates the costly and technically demanding necessity for rapid film sequences.

Vessel diameter measurement using digital subtraction radiography.

A method for obtaining absolute diameter and cross-sectional area measurements on subtraction digital images is described and tested in phantom vessels from 1.5 to 5.5 mm in diameter filled with iodine contrast at concentrations from 23 to 185 mg I/ml. A highly linear correlation of true vs. calculated diameter is demonstrated, with accuracy and reproducibility of the method varying from +/- 1% to 2% at the highest iodine concentration to +/- 30% in the smallest tube at the lowest concentration. A method is described for correction of the observed video density values to allow for nonlinearity of response of the imaging system to iodine density, and its effect on the measured diameters is demonstrated.

Comparison of dual-energy and conventional chest radiography for nodule detection.

This paper presents the results of a nodule detection study, using a Humanoid chest phantom, which was designed to evaluate the performance of two types of dual-energy and conventional (single-energy) chest radiography. The film-screen apparatis were used as image detectors for all imaging modalities. The area under the ROC curve and the cumulative true-positive fraction both were used as performance indexes in the evaluation. Because of the small number of false-positive responses in the observer studies, the cumulative true-positive fraction was eventually regarded as a more conclusive index of accuracy than the area under the ROC curve to make a reasonable conclusion. Both dual-energy techniques, dual- and single-exposure, were found to be superior to conventional chest radiography, P less than 0.0005 and P less than 0.006 for dual- and single-exposure techniques, respectively. The difference between the two dual-energy techniques was statistically insignificant, P less than 0.47. We concluded that the dual-energy, single-exposure technique is worthy of further clinical study based on these encouraging results and because of the ease with which the technique can be implemented.

Cross-sectional area measurements by digital subtraction videodensitometry.

A method for measurement of absolute cross-section areas in digital images of iodine-opacified vessels was tested in phantoms containing "normal" segments of circular cross-section and either circular or noncircular "stenoses" over a wide range of iodine concentrations. Accuracy varied with iodine concentration, with a slight tendency to overestimate the area at high concentration (185 mg I/ml) and to underestimate at low concentration (23 mg I/ml). Reproducibility was improved at the higher concentrations, with standard deviation ranging from 2% to 7% of the measured value, compared with 7% to 27% at the lowest concentration. Accuracy and reproducibility of area measurements on either normal or stenotic segments were unchanged by rotation of the vessel by up to 25 degrees out of the plane of the image. This method is easily implemented using computerized image processing techniques and has advantages over either manual or automated edge detection because it eliminates the need for an edge criterion and is independent of the viewing projection.

Effectiveness of antiscatter grids in digital subtraction angiography.

An analysis of the potential value of antiscatter grids for digital subtraction angiography (DSA) is presented. Using the Rose criterion for signal detection, and assuming quantum limited statistical noise, it is shown that grid selectivity and primary transmission are the two most important parameters of grid performance for DSA. In comparison with conventional grids commonly in current use in radiology departments, a grid having a higher level of primary transmission, (approximately 90%) and a moderate level of selectivity (approximately 6) could provide comparable imaging signal-to-noise ratios, but with 20% to 45% smaller patient dose. Implications of these results are discussed.

Real-time digital K-edge subtraction fluoroscopy.

We report in vitro and in vivo trials of K-edge fluoroscopy, by which iodine contrast concentration is displayed live, with tissue and bone images suppressed, free of patient-motion artifacts. Iodine and cerium, 125 and 225 mg/cm2 respectively, filter alternate TV fields of cine-pulsed 50 KVP x-rays. Weighted subtraction of successive TV fields isolates the iodine image and simultaneously minimizes artifacts. Digital techniques are used in real time. At our present x-ray tube limit, 500 mA instantaneous current, the patient exposure is 180 mR/sec and quantum mottle limits the image quality. Integrating four successive difference images provides a compromise between mottle and smoothly moving displays. Cardiovascular images of a 17-kg dog, using 1 ml/kg Renografin-60 injected into a foreleg vein, show that a 15-cm chest thickness is our present practical maximum. This method may be useful in diagnosing cardiovascular anomalies in infants without catheterization or suspension of breathing.

Quantitative digital subtraction coronary angiography using videodensitometry. An in vivo analysis.

A videodensitometric method for measuring absolute cross-sectional area and diameter has been tested in living dogs with coronary artery stenoses created surgically by placement of small Silastic cuffs. Coronary arteriograms were performed using a circular tomographic unit to provide multiple views of each lesion, and measurements were made from logarithmically subtracted digital images. Dimensions of 13 stenoses of cross section 1 to 5 mm2 and adjacent reference segments (2 to 9 mm2) were determined by histologic sectioning of the segments after injection with a rapidly hardening plastic fixative under physiologic pressure. Two different methods were tested for calculating cross-sectional area. On 238 measurements, 102 of normal vessel segments and 135 of stenoses, both methods showed good correlation with histologic measurements, with slopes of 0.929 + (SD) 0.037 (r = 0.8563) and 0.948 + (SD) 0.037 (r = 0.8554). Multiple measurements of each segment produced values within 30% of the true absolute cross sectional area in most cases. The method shows promise as a means for quantitating absolute dimensions of vessels in clinical arteriography.

Rabbit pneumothorax. Feasibility of an animal model to simulate neonatal pneumothorax.

RATIONALE AND OBJECTIVES: The feasibility of developing an animal model to simulate radiographic features of neonatal pneumothorax was investigated, and supine computed radiography (CR) and film-screen radiography (FS) images were compared. METHODS: 5-Fr pigtail catheters were inserted into the right pleural space of three New Zealand white rabbits. Two CR and two FS supine images were obtained using identical technique. After serial 4-mL injections of air, one CR and one FS supine image were obtained. The images were masked and randomized, and four radiologists reviewed the images for typical signs of pneumothorax. Chest computed tomography (CT) was performed before the injection of any air and after completion of the study. RESULTS: At zero-mL air volume, radiologists did not perceive a pneumothorax. As the air volume increased, the number of signs of a pneumothorax increased; there was no significant difference between CR and FS in the number of signs of pneumothorax detected at any volume. Chest CT confirmed that there was no unexplained air leak. The volume of air injected correlated with the calculated volume from the CT. CONCLUSIONS: This induced, volume-controlled, animal model simulated the supine radiographic features of neonatal pneumothorax.

Computerized fluoroscopy techniques for intravenous study of cardiac chamber dynamics.

A computerized fluoroscopy system which was recently developed in our laboratories permits image contrast increases of 8-16 relative to conventional image intensifer fluoroscopy and permits study of canine and human ventricular wall motion using peripheral intravenous injections. Two time-dependent image subtraction algorithms are illustrated in connection with observation of artificially infarcted dog hearts. The first algorithm produces a display analogous to direct ventriculography using catheterization. The second displays regions of dyskinetic motion as anomalous image grey shades.

Computerized arteriography of the cerebrovascular system: its use with intravenous administration of contrast material.

A unique method of computerized image enhancement makes it possible to visualize the arterial system by intravenous (IV) injection of small doses of standard contrast agent. This technique has been used to study the intracranial and extracranial circulation of more than 100 patients. Occlusion, stenosis, aneurysmal change, plaquing, and ulceration can be identified by computerized IV arteriography. Failures (less than 10%) results from inadequate venous access, extravasation of dye, or patient motion. This technique avoids the need for arteriography. The major risk of IV arteriography is contrast medium reaction. There is a close correlation between IV and standard arteriographic images. Intravenous arteriography does not require hospitalization, is suited for repetitive testing, and has promise as a method of diagnostic screening for stroke prevention.

Real-time digital subtraction angiography for therapeutic neuroradiologic procedures.

Procedural control during therapeutic neuroradiologic procedures is generally based on repeated angiograms to assess the degree to which embolization has reduced abnormal blood flow. Due to the complex craniofacial skeletal anatomy that is superimposed over lesions in this area, subtraction studies are usually required to see the vessels and visualize a tumor stain satisfactorily. We have used a device incorporating continuous recursive digital video filtration, which allows the operator to view a subtracted fluoroscopic image of each control angiographic sequence in real time. The advantages of this technique for therapeutic procedures are described.

Tomographic DSA using temporal filtration: initial neurovascular application.

A preliminary study showed that encouraging laboratory results reported previously using tomographic digital subtraction angiography (DSA) can be transferred to clinical application for neurovascular imaging. Tomography may show cervical carotid disease more clearly than standard DSA images, and it eliminates the interference caused by overlapping vessels. Production of multiple tomographic image planes from a single set of projection data, tomosynthesis, must be incorporated into this imaging system before tomographic DSA becomes clinically useful. This is a practical reality with the present equipment; clinical evaluation of this new capability is underway.

Intravenous video arteriography of the intracranial vasculature: early experience.

A computerized fluoroscopic apparatus developed by members of the University of Wisconsin Medical Physics Section was used for 12 months to perform intravenous video arteriography. In previous papers, the apparatus was described and its use was illustrated for performing time subtraction intravenous video arteriography of the extracranial carotid arteries, the arteries of the abdomen and extremities, as well as angiocardiography. In this report, the use and current limitations of this technique for evaluation of the intracranial vasculature are described and illustrated.

Photoacoustic ultrasound.

Differential absorption has been detected and localized in three-dimensions by recording the photoacoustic pulses that were produced when short-duration (approximately 1 microsecond) pulses of electromagnetic energy were absorbed regionally within a turbid medium. These absorption sites were localized with a spatial resolution of approximately 6 mm within a 20 x 20 x 7.5-cm3 volume of 0.3% Liposyn solution, a highly scattering medium. A Xenon flashlamp, delivering a nominal 1 microsecond pulse of broadband light, was used to irradiate the Liposyn solution. Photoacoustic echoes were recorded with a focused, ultrasonic transducer, tuned to a nominal frequency of 0.5 MHz. The spatial resolution that was demonstrated is consistent with the expected ultrasonic properties of the transducer. Improved spatial resolution can be expected with shorter-duration radiation exposure and higher-frequency transducer designs. The technique is generalizable to any electromagnetic energy range (including long-wavelength microwaves) that penetrates the medium and produces differential, regional absorption of energy.

Estimation of the diameter of and iodine concentration within blood vessels using digital radiography devices.

A variety of digital radiographic and fluoroscopic devices have been developed which can isolate small concentrations of iodine within the cardiovascular system. Using these devices, time dependent subtraction images have been formed which only display opacified vasculature. Theory is presented and simple methods have been developed for determining vessel diameters and iodine concentration from such subtraction images. The methods have been verified using plexiglass and aluminum vessel phantoms imaged with a computerized radiography device. Using this device the diameter of a 5 mm diameter vessel could be determined to within 6% (0.28 mm) even though the pixel width in the digitized image corresponded to 1.34 mm. In the same vessel, it is estimated that an iodine concentration of 46 mg/cm3 could be determined with 10% accuracy.

A method for time domain filtering using computerized fluoroscopy.

A new computerized fluoroscopy technique for isolating low image contrast, which results during the flow of an intravenously administered bolus of iodinated contrast materials, is proposed. The technique requires the application of one of a family of imaging algorithms which have been designed to isolate time varying image contrast. This family of imaging algorithm is described, as is the way in which each isolates a particular range of temporal frequency components associated with the bolus's flow through various cardiovascular structures. The implementation of these algorithms in real time using appropriate digital recursive filtering techniques is described. The architecture of a dedicated hardwired computerized fluoroscopy apparatus which would incorporate these algorithms is also presented.

Dual-energy electronic scanning-slit fluorography for the determination of vertebral bone mineral content.

A technique for performing accurate bone mineral content (BMC) determination, using dual-energy scanning-slit fluorography, has been developed. X-ray scatter and veiling glare are suppressed using a multiple scanning-slit device interfaced to a conventional digital subtraction angiography system. The technique employs a pair of calibration step wedges, one tissue and one bone equivalent. The proper use of the step wedges obviates the need for accurate kVp calibration or absolute calibration of the system's response to BMC. Phantom studies intended to simulate vertebral BMC measurement indicate that the technique is capable of measuring BMC with less than 30 mg/cm2 inaccuracy over a wide range of BMC.

Photoacoustic ultrasound: pulse production and detection of 0.5% Liposyn.

Theoretical predictions and experimental measurements of photoacoustic pulse production within a 0.5% solution of Liposyn, a highly scattering, optical propagation medium, are reported. A simple model for photoacoustic energetics is developed that predicts photoacoustic signal pressure as a function of depth within a turbid medium following surface irradiation from an infrared source. The model is valid for very short irradiation duration. The model predicts that the acoustic pressure produced at a distance r from the center of a small, highly absorbing sphere of radius R consists of two, opposite polarity pulses, one originating from the near and one from the far side of the sphere. The magnitude of these biphasic pulses is expected to be proportional to the energy fluence (E) incident on the surface of the sphere and to the ratio, R/r. Furthermore, the energy fluence (E) that reaches the sphere is roughly proportional to e-mu effZ, where mu eff is the effective attenuation coefficient of the turbid medium and Z is the depth of the embedded sphere below the irradiated surface. The variation of E with depth within the absorber and biphasic acoustic pulse production have been verified experimentally. Further experiments demonstrate that a small (3-mm diameter), highly absorbing sphere can be detected and localized at a depth of 37.5 mm within a 0.5% solution of Liposyn with a spatial resolution of 1 x 6 mm2, using a biologically safe level of infrared irradiation (lambda = 1064 nm) and a conventional ultrasound transducer (frequency = 2.25 MHz). These results suggest that photoacoustic ultrasound imaging may have application to biologic systems such as the human breast.

Dual-slice spiral versus single-slice spiral scanning: comparison of the physical performance of two computed tomography scanners.

In this paper we deal with two types of spiral scanners; one is a single-slice spiral scanner, while the other employs dual-slice technology into spiral scanning. Physical performance parameters, including image noise, contrast resolution, spatial resolution (transversal and longitudinal), and radiation exposure are measured. Computer simulations based on two interpolation methods (180 degrees and 360 degrees linear interpolation) are also used in evaluating the slice-sensitivity profile (SSP) and noise. The results show that the noise behaves in the same way for both types of scanners. The noise change, relative to that of the standard scan with the same scanning parameters, depends solely on the interpolation algorithm. Table speed and scanner geometry (either single slice or dual slice) have no effect on the noise value. For the given table speed, as well as individual detector collimation (slice width) the dual-slice scan results in better longitudinal resolution (SSP) compared to a single-slice scan if the scan is obtained with nonoverlapping slices (pitch greater than 2). This is because the dual-slice scan obtains twice the number of nonoverlapped projections for the same length, which reduces the degradation of the slice profile by using more densely arranged projections (in the longitudinal direction) for the interpolation. In the dual-slice scanner the workable scan rate is extended up to pitch 4 compared to a pitch of 2 for the single-slice scanner. Therefore, the dual-slice spiral scanner is preferred in applications requiring an increased scan rate with comparative image quality.

Scatter estimation for a digital radiographic system using convolution filtering.

The use of a convolution-filtering method to estimate the scatter distribution in images acquired with a digital subtraction angiography (DSA) imaging system has been studied. Investigation of more than 175 convolution kernels applied to images of anthropomorphic head, chest, and pelvic phantoms using 15-, 25-, and 36-cm fields of view (digitized onto a 512 X 512 pixel image matrix) showed that two-dimensional exponential kernels with a full width at half maximum (FWHM) of 50-150 pixels best reproduced the scatter fields within these images with a root-mean-square percentage error from 4% to 8%. A two-dimensional exponential kernal with a FWHM of 75 pixels in each dimension applied to ten different anatomic presentations and fields of view, resulted in an average root-mean-square percentage error of 6.6% for the ten cases studied. The method should be implementable using an array of small lead beam stops placed in the field of only a single mask image and the above described convolution kernel applied to both mask and postopacification images. The mask beam-stop data are used to scale both mask and postopacification convolution-filtered images. This scaled, convolution-filtered image is then subtracted from the original image to produce a largely scatter-corrected image.