SU-E-I-54: Evaluation of High Contrast Resolution for Model Based Iterative Reconstruction of Sinus Examinations

PURPOSE

To evaluate high contrast resolution of Model Based Iterative Reconstruction used with typical sinus examination acquisition parameters.

METHODS

MBIR has recently become available as a recon option on a clinical scanner (Discovery HD750, GE Healthcare). In this work, we evaluate high contrast resolution for scan and reconstruction options that are available for sinus examinations. For this study we used our adult sinus CT protocol reconstructed with filtered back projection, and two alternative scans reconstructed with IR. Our conventional adult sinus CT protocol utilizes a high resolution scan mode which is not compatible with the scanner's IR recon option. The two additional scans are with high resolution option off, one with the head SFOV, and one with the body SFOV. Using IR and the head SFOV, reconstructed images have a 1024 × 1024 pixel matrix. Using IR and the body SFOV, reconstructed images have a 512 × 512 pixel matrix. Three evaluations of high contrast resolution are made for these images. A wire phantom is scanned for assessment of image modulation transfer function. The bar patterns of the ACR phantom are visually assessed for quality in both axial and coronal reformats.

RESULTS

MTF curves show 50% values of 6.8, 7.5, and 7.7 lp/cm for Body IR 512 × 512, Head IR 1024 × 1024, and filtered back projection with HD Bone kernel. The 10% MFT curves for these reconstructions are 11.2, 11.9, and 12.1 lp/cm. Visual evaluation of the ACR phantom at 15 cm display field of view demonstrates resolution of the 10 lp/cm bar patterns for all reconstructions with better visualization of the axial versus coronal recons.

CONCLUSIONS

MBIR reconstruction demonstrates high contrast resolution that is comparable with our conventional sinus examination.

Soft-copy quality control of digital spot images obtained by using X-ray image intensifiers

PURPOSE

To evaluate 12 x-ray image intensifier (XRII) digital spot systems.

MATERIALS AND METHODS

Four objective tests were performed to assess XRII digital spots: entrance exposure, patient exposure, soft-copy gray scale, and pixel noise. Two additional tests were performed to assess high-contrast limiting resolution and threshold contrast detection.

RESULTS

Digital spot XRII entrance exposures averaged 1 x 10(-7) C/kg (0.38 mR) for units with large fields of view (FOVs); mean entrance exposure in a medium-sized patient was 1. 25 x 10(-5) C/kg (48 mR). Luminance measurements of the table-side monitors provided a mean of 473 just-noticeable differences in gray scale with the room lights off. Mean resolution with a bar test pattern was measured as 1.5 line pairs per millimeter for systems with a 40-cm FOV. Measured pixel noise (in relative units) was 6-25. Mean threshold contrast with the lights off was 0.85%.

CONCLUSION

Once input exposure is normalized for FOV and image matrix size, soft-copy assessment of limiting resolution with either low-contrast detection or, preferably, an off-line noise metric (pixel SD) provides objective measurements of digital spot image quality. With the lights on, 10 systems with room-light sensors had an 11% loss of gray scale. For systems without sensors, the loss was 33%.

Active matrix liquid crystal displays for clinical imaging: comparison with cathode ray tube displays

Fifteen large-area, flat-panel displays used for clinical image review were evaluated for image quality and compared with 30 comparably sized cathode ray tube (CRT) monitors. Measurements were of image display patterns by Video Electronic Standards Association (VESA) and a commercial product. Field measurements were made of: maximum and minimum luminance, ambient lighting, characteristic curve (gamma), point shape and size, high-contrast resolution, uniformity, and distortion. Assessments were made of pixel defects, latent image patterns, ghosting artifacts, and viewing angle luminance. Also, a questionnaire was generated for users of the flat-panel and CRT units. Seventeen respondents indicated no preference for either flat panel or CRT. Results show these flat panels to have higher luminance (mean, 177.7 cd/m2); larger number of just noticeable differences (JNDs; n = 555), higher gamma, comparable uniformity, and warm-up time. CRTs had less angle viewing dependence and far fewer artifacts (ghosting and latent images). Our questionnaire showed active matrix liquid crystal displays (AMLCD) to be fully acceptable for clinical image viewing. Furthermore, the statistical results show that further testing for new AMLCDs of this type is unwarranted.

Performance and function of a desktop viewer at Mayo Clinic Scottsdale

A clinical viewing system was integrated with the Mayo Clinic Scottsdale picture archiving and communication system (PACS) for providing images and the report as part of the electronic medical record (EMR). Key attributes of the viewer include a single user log-on, an integrated patient centric EMR image access for all ordered examinations, prefetching of the most recent prior examination of the same modality, and the ability to provide comparison of current and past exams at the same time on the display. Other functions included preset windows, measurement tools, and multiformat display. Images for the prior 12 months are stored on the clinical server and are viewable in less than a second. Images available on the desktop include all computed radiography (CR), chest, magnetic resonance images (MRI), computed tomography (CT), ultrasound (U/S), nuclear, angiographic, gastrointestinal (GI) digital spots, and portable C-arm digital spots. Ad hoc queries of examinations from PACS are possible for those patients whose image may not be on the clinical server, but whose images reside on the PACS archive (10TB). Clinician satisfaction was reported to be high, especially for those staff heavily dependent on timely access to images, as well as those having heavy film usage. The desktop viewer is used for resident access to images. It is also useful for teaching conferences with large-screen projection without film. We report on the measurements of functionality, reliability, and speed of image display with this application.

Quality-of-service improvements from coupling a digital chest unit with integrated speech recognition, information, and picture archiving and communications systems

Speech recognition reporting for chest examinations was introduced and tightly integrated with a Radiology Information System (RIS) and a Picture Archiving and Communications System (PACS). A feature of this integration was the unique one-to-one coupling of the workstation displayed case and the reporting via speech recognition for that and only that particular examination and patient. The utility of the resulting, wholly integrated electronic environment was then compared with that of the previous analog chest unit and dedicated wet processor, with reporting of hard copy examinations by direct dictation to a typist. Improvements in quality of service in comparison to the previous work environment include (1) immediate release of the patient, (2) decreased rate of repeat radiographs, (3) improved image quality, (4) decreased time for the examination to be available for interpretation, (5) automatic hanging of current and previous images, (6) ad-hoc availability of images, (7) capability of the radiologist to immediately review and correct the transcribed report, (8) decreased time for clinicians to view results, and (9) increased capacity of examinations per room.

Performance and function of a high-speed multiple star topology image management system at Mayo Clinic Scottsdale

Mayo Clinic Scottsdale (MCS) is a busy outpatient facility (150,000 examinations per year) connected via asynchronous transfer mode (ATM; OC-3 155 MB/s) to a new Mayo Clinic Hospital (178 beds) located more than 12 miles distant. A primary care facility staffed by radiology lies roughly halfway between the hospital and clinic connected to both. Installed at each of the three locations is a high-speed star topology image network providing direct fiber connection (160 MB/s) from the local image storage unit (ISU) to the local radiology and clinical workstations. The clinic has 22 workstations in its star, the hospital has 13, and the primary care practice has two. In response to Mayo's request for a seamless service among the three locations, the vendor (GE Medical Systems, Milwaukee, WI) provided enhanced connectivity capability in a two-step process. First, a transfer gateway (TGW) was installed, tested, and implemented to provide the needed communication of the examinations generated at the three sites. Any examinations generated at either the hospital or the primary care facility (specified as the remote stars) automatically transfer their images to the ISU at the clinic. Permanent storage (Kodak optical jukebox, Rochester, NY) is only connected to the hub (Clinic) star. Thus, the hub ISU is provided with a copy of all examinations, while the two remote ISUs maintain local exams. Prefetching from the archive is intelligently accomplished during the off hours only to the hub star, thus providing the remote stars with network dependent access to comparison images. Image transfer is possible via remote log-on. The second step was the installation of an image transfer server (ITS) to replace the slower Digital Imaging and Communications in Medicine (DICOM)-based TGW, and a central higher performance database to replace the multiple database environment. This topology provides an enterprise view of the images at the three locations, while maintaining the high-speed performance of the local star connection to what is now called the short-term storage (STS). Performance was measured and 25 chest examinations (17 MB each) transferred in just over 4 minutes. Integration of the radiology information management system (RIMS) was modified to provide location-specific report and examination interfaces, thereby allowing local filtering of the worklist to remote and near real-time consultation, and remote examination monitoring of modalities are addressed with this technologic approach. The installation of the single database ITS environment has occurred for testing prior to implementation.

Blood flow velocity measurements: a comparison of 25 clinical ultrasonographic units

A blood-mimicking flow phantom was used to evaluate the precision of velocity measurements acquired using 25 pulsed Doppler ultrasonographic units from four vendors. Measurements were made at four constant flow rates (12 to 50 cm/s peak velocity). The average standard deviation values of the peak and time-averaged velocities among all units and all flow rates were found to be 7 and 9% of the mean, respectively, while the corresponding values for a subgroup of 20 identical units were 5 and 8%. Considered in conjunction with other published data, this suggests that units should be calibrated to an institutional standard at the time of acceptance testing.

A survey of radiation oncologists regarding their radiation physics instruction

The American Association of Physicists in Medicine, Committee on Training of Radiologists conducted a survey of radiation oncologists requesting information regarding their radiation oncology physics training. General questions were asked of the oncologist regarding their radiation oncology practice such as number of oncologists, number of new patients treated, and the size and type of facility in which the practice is located. The oncologist also responded to questions regarding their educational background. The survey requested the radiation oncologists to answer questions regarding the adequacy and importance of their training in specific areas of radiation physics. The responders indicated that the importance of most physics topics in their clinical practice corresponded to the level of their understanding. The survey indicated that for most radiation oncologists their physics instruction was an important and interesting part of their residency program.

Magnetic resonance with marked T2-weighted images: improved demonstration of brain lesions, tumor, and edema

The object of this study was to determine the sensitivity of magnetic resonance (MR) for imaging intracranial lesions with heavily T2-weighted images compared with that of computed tomographic (CT) and T1-weighted images. Fifty-five patients with known intracranial pathology consisting of primary neurogenic tumors, brain infarcts, demyelinating disease, and metastases were studied by MR and CT. Patients were studied with either 0.6 or 1.5 T systems with T1- and T2-weighted radiofrequency pulse sequences. The heavily T2-weighted images were found to be superior to the T1-weighted images in terms of sensitivity, with 168 lesions found versus 86 by CT and 104 by T1-weighted imaging.

Gated cardiac magnetic resonance structural imaging: optimization by electronic axial rotation

Most magnetic resonance imaging has used body orthogonal axes with the Z axis placed along the length of the body and the X and Y axes at right angles to the body. This orientation is not optimum for the heart; visualization of sections along the short and long cardiac axes would best define cardiac structural detail and functional status. The new orientation was accomplished by selection of electronic angulation of the magnetic fields for each subject rather than by attempting to approximate the cardiac axes by altering the position of the patient. This technique improved visualization of comparative wall segments, valvular structures, and the true four-chamber view of the heart, and also gave the best visualization of the pericardium. In addition, more accurate estimates of chamber size and myocardial mass can be made from the short-axis orientation, since the sections are orthogonal to the myocardium.

Clinical and in vitro magnetic resonance imaging of prostatic carcinoma

Magnetic resonance imaging (MRI) of the prostate was accomplished in 10 patients who subsequently had surgical exploration for histologic confirmation and tumor staging. Eight patients were found to have carcinoma of the prostate. Two patients had malignancies of the urinary bladder and were treated with radical resection of the bladder and prostate. The prostatic glands in the latter two patients were free of tumor. One gland was entirely normal; the other had extensive acute and chronic prostatitis. Two resected prostates with carcinoma and one normal prostate were available for in vitro MRI in a clinical magnetic resonance unit. The MRI finding of prostatic carcinoma was heterogeneous signal patterns, seen best on T2-weighted studies. A similar pattern was identified in the gland with acute and chronic prostatitis. There was a homogeneous MRI signal pattern of the normal prostate gland examined in vitro. In two instances, the MRI studies were accurate for the identification of tumor spread to the seminal vesicles, not diagnosed at the time of surgical resection. Microscopic metastatic disease of the lymph nodes in four patients was not identified by MRI.

Magnetic resonance imaging of intervertebral disk disease. Clinical and pulse sequence considerations

Sixty-five patients were examined with magnetic resonance imaging (MR) to determine what combination of operator-selectable controls would result in a thorough examination of the intervertebral disks. There were 20 normal subjects, 8 with degenerative lumbar disk disease, 27 with both degeneration and herniation, 5 with stenosis of the spinal canal, and 5 with disk space infection. T2 was significantly longer in the normal nucleus pulposus than in the degenerated disk. Based on plots of in vivo signal intensity vs. repetition time (TR) for various echo times (TE), a sagittal 30-msec. TE and a 0.25-sec. TR were used for anatomical delineation and rapid localization, while sagittal and/or axial 120-msec. TE/3-sec. TR images were used to evaluate the cerebrospinal fluid and disk. Comparison with radiographs, high-resolution CT scans, and myelograms showed that MR was the most sensitive for identification of degeneration and disk space infection, separating the normal nucleus pulposus from the annulus and degenerated disk. Herniation, stenosis of the canal, and scarring can be identified as accurately with MR as with CT or myelography.

The special environmental needs of magnetic resonance

The addition of a magnetic resonance (MR) unit to a hospital radiology environmental poses many unique considerations. Large magnetic fields present health and safety considerations as well as a hostile environment for data recorded magnetically. Radio-frequency shielding is necessary to eliminate a source of background signal that interferes with patient examinations. Magnetic shielding may be necessary in some instances to prevent low-level magnetic field exposure of persons with artificial cardiac pacemakers. Superconducting magnets are heavy and large and may give off large amounts of helium which can temporarily replace the air in the magnet room. Possible solutions to these environmental requirements are presented.

Magnetic resonance imaging of the cervical spine: technical and clinical observations

Seventy-two patients were examined to determine the clinical potential for magnetic resonance imaging (MRI) of the spine. MRI using different pulse sequences was compared with plain radiography, high-resolution computed tomography, and myelography. There were 35 normal patients; pathologic conditions studied included canal stenosis, herniated disk, metastatic tumor, neurofibroma, trauma, Chiari malformation, syringomyelia, arteriovenous malformation, and rheumatoid arthritis. MRI provided sharply defined anatomic delineation and tissue characterization. It was diagnostic in syringomyelia and Chiari malformation and was useful in the evaluation of trauma and spinal canal block from any cause. MRI was sensitive to degenerative disk disease and infection. The spin-echo technique, with three pulse sequence variations, seems very promising. A short echo time (TE) produces the best signal-to-noise ratio and spatial resolution. Lengthening the TE enhances differentiation of various tissues by their signal intensity, while the combined increase of TE and recovery time (TR) produces selective enhancement of the cerebrospinal fluid signal intensity.

NMR imaging of the abdomen: technical considerations

Evaluation of nuclear magnetic resonance (NMR) imaging of the abdomen was done in 41 patients with focal and diffuse disorders of the liver and retroperitoneal and vascular abnormalities. Spin-echo technique was used in each situation with varying time to echo (TE) and repetition rates (TR). No single pulsing technique was optimal in all situations. Three false-negative NMR studies of 22 patients with focal lesions of the liver were attributed to incomplete coverage of the involved area or inappropriate pulsing technique. When appropriate technique was achieved, NMR was equal to computed tomography (CT) in detecting abdominal disorders, except in fatty infiltration of the liver. NMR was superior to CT in imaging vascular anatomy because of the inherent increased contrast produced by the absence of signal from flowing blood and the flexibility of imaging planes.

Digital subtraction angiography in the evaluation of intracranial and extracranial vascular disease

Digital subtraction angiography (DSA) is a method of visualizing the vessels of the body with the intravenous injection of contrast material. Improvements in computers, television systems, and image intensifiers have contributed to the increased image quality of DSA. With DSA, the vessels such as the carotid bifurcations and the intracranial vasculature can be visualized with a 2-3% concentration of contrast material, while with conventional angiography, the concentration of contrast in vessels is 40-50%. Using IV DSA, visualization of the carotid bifurcations is of good or excellent quality 85% of the time. In a high percentage of these cases, IV DSA replaces conventional angiography, although for imaging of the intracranial vessels, IV DSA is not as good as conventional angiography. In most tumor patients, however, conventional intracranial angiography is not needed because IV DSA combined with computed tomography gives sufficient information.

Nuclear magnetic resonance imaging of the spine

Forty subjects were examined to determine the accuracy and clinical usefulness of nuclear magnetic resonance (NMR) examination of the spine. The NMR images were compared with plain radiographs, high-resolution computed tomograms, and myelograms. The study included 15 patients with normal spinal cord anatomy and 25 patients whose pathological conditions included canal stenosis, herniated discs, metastatic tumors, primary cord tumor, trauma, Chiari malformations, syringomyelia, and developmental disorders. Saturation recovery images were best in differentiating between soft tissue and cerebrospinal fluid. NMR was excellent for the evaluation of the foramen magnum region and is presently the modality of choice for the diagnosis of syringomyelia and Chiari malformation. NMR was accurate in diagnosing spinal cord trauma and spinal canal block. The normal disc was seen, but with rare exceptions bulging of the annulus and herniation of the nucleus pulposus were not visualized.

Intravenous digital subtraction angiography: peripheral versus central injection of contrast material

Central and peripheral intravenous injections of contrast material for digital subtraction angiography were compared in 30 patients. With 40 ml of contrast material, visualization of the carotid bifurcations was as good with the peripheral as with the central injection. A more consistently high-quality examination of the small intracranial vessels was obtained with the central injection.

Anatomic and functional imaging of congenital heart disease with digital subtraction angiography

Digital subtraction angiography (DSA) of the heart was performed in 54 patients for the evaluation of congenital heart disorders. DSA produced high-quality diagnostic images and accurate physiologic shunt data that compared favorably with catheter angiography and nuclear medicine studies. Retrospective analysis of this series of patients indicated that DSA studies contributed sufficient information to shorten significantly or modify cardiac catheterization in 85% (79/93) of the defects that were identified. Interatrial septal defects were particularly well diagnosed, with identification occurring in 10 of 10 cases, whereas intraventricular septal defects were identified in only 6 of 9 patients. Evaluation of postsurgical patients was accurate in 19 of 20 cases.

The effects of nuclear magnetic resonance on patients with cardiac pacemakers

The effect of nuclear magnetic resonance (NMR) imaging on six representative cardiac pacemakers was studied. The results indicate that the threshold for initiating the asynchronous mode of a pacemaker is 17 gauss. Radiofrequency levels are present in an NMR unit and may confuse or possibly inhibit demand pacemakers, although sensing circuitry is normally provided with electromagnetic interference discrimination. Time-varying magnetic fields can generate pulse amplitudes and frequencies to mimic cardiac activity. A serious limitation in the possibility of imaging a patient with a pacemaker would be the alteration of normal pulsing parameters due to time-varying magnetic fields.

Digital subtraction angiography of the intracranial vascular system: comparative study in 55 patients

Intracranial vessels were examined in 55 patients with both conventional selective catheterization and intravenous digital subtraction angiography using a prototype digital subtraction unit. In 65% of the patients, the digital subtraction angiogram was diagnostic, but the overall quality was inferior to conventional selective angiography. In 22%, the digital subtraction angiogram provided diagnostic information, but there was a significant chance of misinterpreting the results of the study. In 13% of cases, the subtraction angiogram was not diagnostic. As now developed, digital subtraction angiography can replace conventional cerebral angiography for preoperative evaluation of the juxtasellar carotid artery prior to transphenoidal surgery because the large intracerebral vessels are consistently well visualized with digital subtraction. The dural sinuses are better visualized with digital subtraction than with conventional angiography because with digital subtraction all the vessels of the brain are opacified, whereas with conventional angiography, there is a mixture of opacified and unopacified blood in the sinuses. Combined with computed tomography, digital subtraction angiography can replace conventional angiography for determining the preoperative extent and vascularity of tumors. It can be used for postoperative evaluation of aneurysms, arteriovenous malformations, extracranial to intracranial bypasses, and after the embolization of vascular lesions.

Digital subtraction angiography of the abdominal aorta and renal arteries. Comparison with conventional aortography

Digital subtraction angiography (DSA) was used to study the cardiovascular system in more than 400 patients and was specifically compared with conventional angiography of the aorta and renal arteries in 30 patients. For the renal arteries, the overall accuracy of DSA was 71% (50/70). Excluding 11 cases of inadequate visualization of the renal arteries on DSA, the sensitivity of the new technique was 93% (55/59) and the specificity 91.5% (54/59). Aortic disease, including intravascular clots and occlusions, was faithfully delineated by DSA.

Imaging capability of an experimental digital subtraction angiography unit

We evaluated an experimental digital subtraction unit in terms of field uniformity, linearity of signal response to x-radiation, response of the log amplifier, and imaging capability as measured with the Rose phantom. For comparison, conventional film subtraction phantom measurements were made. Our results indicate that this unit exhibits greater sensitivity to contrast media than conventional film subtraction units.

Digital subtraction angiography of the human cardiovascular system

Initial clinical application of a system for digital subtraction angiography (DSA) to the human cardiovascular system in 88 patients is reported. The equipment consisted of a specially designed computer system integrated with a fluoroscopic and radiographic apparatus for digitization, manipulation, and display of data. After intravenous injection of contrast material, adequate visualization of the heart and carotid, thoracic, abdominal, and femoral arteries was obtained with sufficient quality to obviate conventional angiography in many clinical settings. In this mode, nonselective opacification is obtained. However, DSA was also used to extend the capability of selective angiography. The availability of quantitative information permitted the determination of rates of transit of contrast material in various organs which may give insights of their physiologic performance.