A practical approach to 64-slice coronary CT angiography

Coronary computed tomography angiography with 64-slice multidetector CT scanners allows reproducible and accurate non-invasive evaluation of coronary atherosclerotic disease in most patients. These coronary CT angiography studies are very promising and exciting. However, the start-up phase of such a coronary CTA program can be challenging. We discuss the problems that one can encounter during start up of such a coronary CTA program and possible solutions. Training of the technologist, time-management and communication with the referring physician are key aspects of a successful coronary CTA program.

Adenocarcinoma of the ileum in Crohn disease

Small bowel adenocarcinoma develops in 1.5% of patients who have longstanding Crohn disease and is very rarely diagnosed preoperatively because of its rarity, overlapping imaging features, and lack of reported cases. Nonspecific findings including loss of mural stratification (i.e., "target sign") and mild degree of bowel wall enhancement when combined with enlarged mesenteric lymph nodes were helpful computed tomographic findings to suspect malignancy in our case.

3D MR imaging of coronary arteriovenous fistulas

Coronary arteriovenous fistula are uncommon if not rare, but represent the most prevalent hemodynamically significant congenital malformations of the coronary arterial circulation. The goal of this report is to evaluate the use of 3D volume rendering from transaxial breathhold coronary MR angiograms to visualize coronary arteriovenous fistulas. Coronary MR angiography offers a new non-invasive technique that accurately defines the anatomy of these malformations, setting the stage for surgical intervention.

Imaging of coronary artery disease--MR

The noninvasive imaging of normal and diseased coronary arteries by magnetic resonance angiography (MRA) has undergone numerous technical improvements since its introduction in 1993 but remains a work in progress. This paper will review the current status of coronary MRA with a focus on the history of coronary MRA and current limitations of the technique. The technical challenges that need to be addressed if this technique is to achieve widespread use for coronary artery evaluation will be discussed.

Breathhold cine MRI of left ventricular function in patients with obstructive sleep apnea: work-in-progress

Obstructive sleep apnea (OSA) is a sleep-related breathing disorder that can cause left ventricular (LV) dysfunction. In patients with OSA, the LV dysfunction is usually evaluated by echocardiography. The purpose of this study was to evaluate whether the use of breathhold cine MRI for the study of LV dysfunction would be feasible and well tolerated by patients with OSA. Six volunteers and five patients underwent a breathhold cine MRI study of the LV using a 1.5 Tesla MR imager. Cine MRI was performed using a breathhold k-space segmented TurboFLASH technique during end-expiration. Systolic thickening of the LV septal wall was 49% +/- 16% in normals vs. 25% +/- 10.5% in patients (p < 0.05). Systolic thickening of the LV free wall was 42% +/- 12% in normals vs. 22% +/- 9% in patients (p < 0.05). There was a significant difference in end-diastolic wall thickness between the two groups. All patients tolerated the procedure well. The total duration of each study was relatively short (less than 11 min). Breathhold MRI techniques can be used to study LV dysfunction in patients with respiratory disability such as OSA.

Ability to use duplex US to quantify internal carotid arterial stenoses: fact or fiction?

PURPOSE

To determine if duplex ultrasonography (US) can help predict the degree of internal carotid arterial (ICA) stenosis.

MATERIALS AND METHODS

ICA peak systolic velocity (PSV) and the ratio of the PSV in the ICA to that in the ipsilateral common carotid artery (VICA/VCCA) were compared with the degree of arteriographically measured stenosis. ICAs were arteriographically subgrouped at 10% incremental levels of stenosis and broader ranges. Mean PSV, VICA/VCCA, and SDs were calculated for each category. Histograms showing the numbers of stenotic ICAs in subgroups and for vessels with stenoses of greater than or equal to or less than 70% narrowing were constructed. The number of vessels correctly subgrouped with typical Doppler US thresholds was calculated.

RESULTS

Mean PSV and VICA/VCCA increased with stenosis level (P < .01); SDs were wide. Histograms showed Doppler US values in the central groups across all disease levels. Histograms differentiating at least or less than 70% stenosis showed minimal overlap. PSV and VICA/VCCA helped classify, respectively, 185 and 181 of 204 vessels with stenoses of less than 50%, 15 and 21 of 46 vessels with stenoses of 50%-69%, and 73 and 67 of 84 vessels with stenoses of 70% or greater. When classifying stenoses as 69% or less or 70% or more, PSV and VICA/VCCA were correct in 90.6% and 90.3% of vessels.

CONCLUSION

Doppler US is excellent for classifying stenoses as above or below a single degree of severity but does not function well in stenosis subclassification.

Usefulness of coronary MR angiography prior to angioplasty

The range of indications for percutaneous transluminal coronary angioplasty (PTCA) has increased greatly since the procedure was initially introduced. The success rate depends on the anatomy and length of the occlusion and on the state of the distal vessel. We present a case where the use of magnetic resonance angiography (MRA) allowed to evaluate the length of a subtotal occlusion prior to PTCA, and thus could have had an impact on therapeutic decisions. Coronary MR angiography is one of the many applications of breathhold MRI, where breathholding and segmented k-space acquisition are combined to provide anatomical images of coronary vessels. Coronary MR angiography allows reproducible visualization of coronary vessels. Even under adverse circumstances (poor cardiac triggering) the images are sometimes of sufficient quality to help make a diagnosis. This capability may increase the as yet limited clinical use of MR technology in the practice of cardiology.

Planning and cost analysis of digital radiography services for a network of hospitals (the Veterans Integrated Service Network)

This study analysed the design and cost of a picture archiving and communications system (PACS), computerized radiography (CR) and a wide-area network for teleradiology. The Desert Pacific Healthcare Network comprises 10 facilities, including four tertiary medical centres and one small hospital. Data were collected on radiologists' workloads, and patient and image flow within and between these medical centres. These were used to estimate the size and cash flows associated with a system-wide implementation of PACS, CR and teleradiology services. A cost analysis model was used to estimate the potential cost savings in a filmless radiology environment. ATM technology was selected as the communications medium between the medical centres. A strategic plan and business plan were successfully developed. The cost model predicted the cost-effectiveness of the proposed PACS/CR configuration within four to six years, if the base costs were kept low. The experience gained in design and cost analysis of a PACS/teleradiology network will serve as a model for similar projects.

MR imaging of cervical spine motion with HASTE

The HASTE (half-Fourier acquisition single-shot turbo spin-echo) technique delivers images with T2-weighting in about half a second and could be ideal for fast dynamic studies when T2-weighting is needed. We evaluated cardiac-triggered HASTE to study cervical spine flexion/extension. The cervical spines of ten asymptomatic volunteers were studied during flexion/extension motion on a 1.5 Tesla imager using a cardiac triggered version of the HASTE technique. Midline sagittal images were acquired every 2 to 3 s during neck flexion and extension. Image quality was compared to traditional T2-weighted Turbo spin-echo. The study duration per flexion/ extension was typically less than 20 seconds and well tolerated. The cardiac-gated T2-weighted HASTE images compared favorably to the traditional T2-weighted TSE images in quality and overall anatomic detail. Range of motion averaged: flexion 30 degrees (range 8 degrees -48 degrees) and extension 23 degrees (range 0 degrees -57 degrees ). Greatest motion occurred in the lower cervical spine (C4-C7). At the intervertebral discs the canal diameter, anterior and posterior CSF spaces were widest in neutral position and decreased with flexion and extension. Therefore, Cardiac-gated T2 HASTE sequences provide diagnostic and time-efficient dynamic MR images of cervical spine motion.

Doppler sonographic parameters for detection of carotid stenosis: is there an optimum method for their selection?

OBJECTIVE

A wide range of Doppler threshold values for carotid stenosis is found in the literature. We undertook this study to compare methods of derivation and to determine if an optimum strategy of threshold selection exists for a high-risk population.

MATERIALS AND METHODS

From the sonograms of all patent internal carotid arteries, peak systolic velocity in the internal carotid artery (ICA(PSV)) and the ratio of peak systolic velocity in the internal carotid artery to that of the common carotid artery (ICA(PSV)/ CCA(PSV)) were compared with the percentage of angiographically determined stenosis. Receiver operating characteristic curves were generated for levels of stenosis > or =60% and > or =70%. Doppler thresholds were chosen on the basis of maximum accuracy and on the basis of > or =90% sensitivity and specificity. Patients were then segregated into symptomatic and asymptomatic cohorts, and the above process was repeated. An effectiveness analysis was also conducted using various Doppler thresholds. Thresholds derived using these three methods were compared and optimal values chosen. RESULTS. Of 333 carotid arteries that fit inclusion criteria, 132 were found in asymptomatic patients and 201 in symptomatic patients. Maximum accuracy, > or =90% sensitivity and specificity, and effectiveness analysis each produced different ranges of thresholds. We chose final thresholds that maintained patient outcome profiles. For asymptomatic patients at the > or =60% stenosis level, thresholds were ICA(PSV) = 200 cm/sec and ICA(PSV)/CCA(PSV) = 3.0. For symptomatic patients with stenosis > or =70%, thresholds were ICA(PSV) = 175 cm/sec and ICA(PSV)/CCA(PSV) = 2.5.

CONCLUSION

Considerable latitude exists in the choice of carotid Doppler thresholds. We propose a rational strategy for threshold selection based on a combination of three commonly used methods. Our observations indicate that it appears advisable to consider symptomatic and asymptomatic patients separately and to apply appropriately derived thresholds.

Coronary MR angiography

MR angiography of the coronary arteries became possible in 1991 with the development of a new group of fast MR imaging sequences. Although the role of coronary MR angiography in screening for coronary artery lesions has not yet been established, coronary MR angiography already has been very successful in the detection of coronary artery variants and the imaging of coronary stents and bypass grafts. Variants of these new MR imaging techniques also can quantitate velocity in native coronary arteries. Several generations of coronary MR angiographic techniques exist; all techniques use EKG-triggering. The use of MR contrast agents appears to further improve all techniques. Technical progress and changes in this subfield of cardiac MR imaging have been so fast that large-scale preclinical trials have not been conducted with the majority of the first and second generation coronary MR angiographic pulse sequences as known today. This article reviews the development of these new cardiac MR imaging techniques and the initial successes with clinical application using commercial MR scanners.

Assessment of coronary artery patency after stent placement using magnetic resonance angiography

The ability to noninvasively assess the patency of coronary stents would represent a significant advance. We evaluated the safety and ability of two-dimensional coronary MR angiography in imaging stents and suggesting patency. Coronary MR angiography of 26 coronary stents (Palmaz-Schatz) was performed in 16 patients 39 to 73 years of age. Studies were performed between 2 and 4 months after stent placement. All patients were symptom free at the time of imaging. Coronary MR angiography was performed with a commercial 1.5-T MR imager using an electrocardiographically gated pulse sequence with breath-holding. Images were obtained in mid-diastole with and without fat suppression. Image artifacts caused by the metal in the stents were clearly visualized in all 26 stents (100% sensitivity for stent detection). Arterial flow signal was seen in the coronary artery or graft distal to the stent in 25 of 26 cases (96%). All patients, except for the one in which distal flow could not be seen, remained symptom free for >2 years. The distribution of stent locations was as follows: 10 in the right coronary artery (RCA), 10 in the left anterior descending coronary artery (LAD), 2 in the left circumflex coronary artery, and 4 in saphenous vein grafts (SVGs) to RCA. One patient had 2 RCA and 2 LAD stents, one had 3 RCA and 1 LAD stents, one had 3 SVG stents, and two had double RCA stents. Coronary MR angiography is safe for noninvasive imaging of coronary stents, and in the proper clinical setting, it can be used to help suggest patency.

Ability of a phase shift US contrast agent to improve imaging of the main renal arteries

PURPOSE

To evaluate the ability of a phase shift contrast agent to improve Doppler sonographic imaging of the main renal arteries in cases of suspected renal artery stenosis.

MATERIALS AND METHODS

In 25 patients in whom renal artery stenosis was suspected, baseline Doppler sonography was performed followed by two studies performed after blinded administration of contrast material or placebo (saline). Each kidney (n = 45) was evaluated for (a) visualization of the main renal artery on a scale of 0-4, (b) presence of accessory renal arteries, and (c) direct Doppler sonographic findings suggestive of renal artery stenosis. Correlative magnetic resonance angiography was performed in 24 patients, and angiograms were obtained in eight kidneys with stenosis at one or both imaging studies.

RESULTS

Contrast enhancement was observed in 23 patients. Enhancement was 8-20 minutes. Renal artery visualization scores improved from a mean of 2.56 and 2.71 on baseline and noncontrast scans, respectively, to 3.69 after administration of contrast material. Contrast-enhanced images depicted seven kidneys with accessory renal arteries not seen at other studies. Two of eight cases of stenosis were seen only with contrast-enhanced sonography.

CONCLUSION

Use of the phase shift contrast agent appears to enable a reduction in the number of equivocal findings of renal artery stenosis.

Picture archiving and communication system-asynchronous transfer mode network in a midsized hospital

This article describes the pathway to full implementation of a hospital information system-picture archiving and communication system-wide area network (HIS-PACS-WAN) in a 300-bed acute care hospital, and the linking of that system to two other off-site medical centers. The PACS included direct digital capture of computed tomography (CT), magnetic resonance (MR) imaging, nuclear medicine, and ultrasonography images into an Olicon archive. Plain radiographs and fluoroscopy images were digitized manually and archived into an Olicon system. The active archive included current images on each Olicon workstation and the juke box. Long-term archiving of the images on removable optical discs, which would be loaded manually by an operator every time a request for one of these studies appeared on the operator's monitor, also was implemented. Ability to store, retrieve, and display simultaneously the physician's report of each procedure along with the images was an ultimate goal. The WAN is to be used for teleradiology and teleconferencing among the three medical centers involved in this study as well as other off-site locations. Phase I included the design and installation of the local area network (LAN) in the Department of Radiology at Olive View-UCLA Medical Center. This included the clinics and the inpatient and hospital-wide fiber-optic network and its linkage to the local telephone company. Phase II involved linkage of the Olicon workstations to imaging equipment. This implementation has been delayed significantly because of inadequate needs assessment, absence of planning for forward-compatibility to imaging equipment, and incompatibilities in DICOM conformance among vendors. Every PACS project must include an in-depth needs analysis, which should be updated yearly because of rapid turnover of technology. Although this analysis should have a heavy emphasis on clinical needs, it must incorporate the hospital-wide needs for an integrated information systems network. Integration of PACS, HIS, RIS, and a dictation/transcription system is a complex task that requires a full-time, clinically oriented project officer for successful completion.

MRI of coronary arteries

Magnetic Resonance Angiography (MRA) of the coronary arteries has recently become possible due to the development of a new group of ultrafast imaging sequences. Although the role of coronary MR angiography in screening for coronary artery lesions has not yet been established, coronary MR angiography has been very successful in the detection of coronary artery variants, and the imaging of coronary stents and bypass grafts. Variants of these new MRI techniques can also quantitate velocity in native coronary arteries. Coronary MR angiographic techniques can be subdivided in breath-hold (single or repeated breath-hold) and non-breath-hold techniques. Most of the clinical experience so far has been with a single breath-hold technique, and was limited to cooperative patients. The recent introduction of navigator pulses for real-time respiratory gating or triggering allows non-breath-hold or repeated breath-hold 3-D coronary MR angiography, and will allow a more widespread use of this technique. Notwithstanding the progress being made and the excitement created by the prospect of a noninvasive coronary artery screening tool, several key technical problems remain unresolved and are now being addressed by the scientific and clinical community. This paper reviews ongoing research in coronary MR angiography.

Ultrafast networks (ATM): first clinical experiences

Ultrafast networks using asynchronous transfer mode (ATM) technology can provide the bandwidth and throughput that may be sufficient to satisfy the medical imaging community. Several trials are underway to assess the effect of ATM network capabilities on the clinical practice of radiology, by providing immediate interactive radiology consultations between subspecialists and general radiologists at affiliated academic institutions. The hardware to build such networks is now commercially available and its cost is decreasing steadily, but the monthly charges for ATM bandwidth use are still high. Nevertheless, given the tremendous increase in communication capability and data transfer rates possible with ATM networks, cost alone should not be the determining factor for selecting this technology. The ATM concept in general is first reviewed, followed by a description of early clinical ATM network installation in four medical environments worldwide. These medical clusters include: the UCLA affiliated hospitals (UCLA Medical Center, West LA VAMC and Olive-View UCLA Medical Center), the UCSF affiliated hospitals, Duke University Hospitals and a cluster of medical centers in Berlin which have all been connected via ATM networks. The use of ATM technology in these realistic clinical environments is discussed and evaluated for its potential impact on patient care and clinical teaching within radiology departments. From this preliminary study it is concluded that image communications over a regional PACS using an ATM network can allow interactive consultations between different subspecialist and general radiologists or other specialized radiologists spread over different medical centers.

Two-dimensional coronary MRA: limitations and artifacts

Our purpose was to assess image quality and interpretation problems of two-dimensional (2D) coronary MR angiograms. The coronary arteries of 27 subjects (12 normal volunteers and 15 patients) were evaluated with 2D coronary MR angiography (MRA). Coronary MRA was performed with a fat-suppressed electrocardiographically gated breath-hold gradient-echo sequence with k-space segmentation using a 1.5-T imager. Image quality throughout the study was occasionally degraded by: image ghosting (22%), ringing (19%), and/or blurring (22%) and incomplete fat-suppression (19%). Intermittent difficulties with breathholding were encountered in 44% of subjects. When limiting the analysis to those images with optimal image quality, interpretative difficulties were sometimes found: misregistration due to inconsistent breathholding (37%); difficulty in distinguishing veins from arteries (37%); obscured anatomy due to overlapping structures (26%); and poor visualization of portions of the left main coronary artery (59%). Two-dimensional coronary MRA studies have image quality and interpretive problems which need to be understood and addressed before routine clinical scanning is initiated.

Coronary MR angiography

The principles underlying coronary MR angiographic pulse sequences are reviewed, including basic coronary anatomy, motion, and flow physiology. Coronary MR angiographic techniques can be subdivided into breath-hold (single or repeated) and nonbreath-hold techniques. The recent introduction of navigator pulses for real-time respiratory gating or triggering allows nonbreath-hold or repeated breath-hold 3-D coronary MR angiography, and will allow a more widespread use of this technique.

MRI of pseudoaneurysm of a brachial venous coronary bypass graft

Coronary artery bypass grafting (CABG) is being performed all over the world, with major success in the management of ischemic heart disease and angina pectoris. Complications of bypass grafting include partial or total graft reocclusion, and less common entities such as aneurysm or pseudoaneurysm formation. Noninvasive imaging procedures exist which can help include or exclude the presence of these unusual types of complications when mass-like abnormalities are seen on a chest X-ray following coronary artery bypass grafting. This case specifically illustrates the usefulness of ultrafast magnetic resonance imaging techniques in the evaluation and diagnosis of pseudoaneurysm formation at the site of coronary artery bypass graft.

Appearance of the normal pericardium on coronary MR angiograms

We evaluated the appearance of the normal pericardium on breath-hold MR images used to visualize coronary arteries. A coronary MR angiogram was obtained in 23 subjects (17 healthy volunteers and six patients with no known pericardial disease) using a breath-hold K-space segmented gradient-recalled echo sequence with fat suppression. Each coronary MR angiographic study included imaging planes equivalent to the following echocardiographic planes: four-chamber view, vertical two-chamber view, and two short-axis views (at base and mid ventricular level). The average pericardial thickness was 1.7 mm (range, 1.5-2.0 mm), and an average length of 60 mm (range, 20-110 mm) of pericardium was visualized. A significantly longer portion of the pericardium was seen in the vertical two-chamber view and the basal short-axis view than in the two other views (P < .001). Normal anatomic variations and overlapping structures and image artifacts can alter the appearance of the pericardium. Breath-hold MR imaging techniques used for coronary MR angiography allow routine, time-efficient evaluation of large portions of the pericardium.

Two-dimensional coronary MR angiography: analysis of initial clinical results

PURPOSE

To assess the diagnostic value of two-dimensional coronary magnetic resonance (MR) angiography in patients evaluate for ischemic heart disease.

MATERIALS AND METHODS

Twenty patients who underwent elective cardiac catheterization with coronary angiography were evaluated with two-dimensional coronary MR angiography. Coronary MR angiography was performed with a fat-suppressed electrocardiographically gated gradient-echo sequence with k-space segmentation with a 1.5-T imager.

RESULTS

Seventeen of the 20 patients had a hemodynamically significant coronary artery lesion (> or = 50% reduction in luminal diameter), with a total of 27 proximal lesions. The sensitivity for detection of hemodynamically significant lesions was 62% for the right coronary artery, 50% for the left main artery, 73% for the left anterior descending artery, and 0% for the left circumflex artery, with an overall sensitivity of 63%. Corresponding specificities were 56%, 84%, 37%, and 82% respectively.

CONCLUSION

Although in an early stage of development, two-dimensional coronary MR angiography can depict 63% of hemodynamically significant coronary artery lesions.

Coronary MR angiography: a review

With the advent of faster magnetic resonance imaging techniques, magnetic resonance angiography (MRA) of the coronary vessels has become a reality. Coronary MRA is a non-invasive imaging technique and preliminary clinical studies appear very promising. Coronary MRA can detect from 63% to 90% of all hemodynamically significant (= 50%) coronary lesions. Typically one can visualize the proximal 5.5 cm of the right coronary artery (RCA), the left main (LM) coronary artery, the proximal 4.5 cm of the left anterior descending (LAD) coronary artery and approximately 1.5 cm of the left circumflex (LCx) coronary artery. The current limitations of coronary MRA include: the inability to visualize the more distal portion of the coronary arteries and coronary artery branches, the need for consistent breath-holding and the need for special patient positioning. Coronary MRA techniques are improving and we feel will become an integral part for the evaluation of patients with ischemic heart disease.

Postoperative evaluation of pulmonary arteries in congenital heart surgery by magnetic resonance imaging: comparison with echocardiography

Palliative and corrective operations for the treatment of cyanotic congenital heart disease frequently involve or potentially influence the size of the pulmonary arteries. Echocardiography and magnetic resonance imaging (MRI) are two noninvasive imaging techniques currently used to assess morphologic abnormalities of the pulmonary arteries. The purpose of this study was to evaluate the role of MRI in comparison with echocardiography for defining morphologic changes of the pulmonary arteries after congenital heart surgery. The MRI scans and echocardiograms of 33 patients with surgery involving or affecting the pulmonary arteries were compared. The pulmonary outflow tract, pulmonary confluence, right and left pulmonary arteries, and surgical shunts were separately evaluated. Cineangiography and surgical reports were used to confirm findings. MRI and echocardiography were equivalent for demonstrating abnormalities of the right ventricular outflow tract, main pulmonary artery, and a variety of pulmonary shunts. MRI was superior to echocardiography in demonstrating abnormalities of the right and left pulmonary arterial branches (p < 0.001). MRI is effective for monitoring pulmonary arterial status after surgery and is superior to echocardiography for the evaluation of the right and left pulmonary arteries.

Valvular heart disease

This article reviews existing magnetic resonance imaging techniques used to evaluate valvular heart disease. Specifically, this article discusses the capabilities of magnetic resonance imaging for (1) the detection and quantification of valvular regurgitation; (2) the detection and quantification of valvular stenosis; (3) the quantification of left ventricular dimension, function, and loading conditions with valvular heart disease; and (4) the monitoring of changes in valvular and ventricular function with time and with therapy.

Cholelithiasis in the gravid Hispanic population

Ultrasound examinations were performed to determine the prevalence of cholelithiasis in 585 pregnant Hispanic patients. The ultrasound findings were correlated with age and country of birth. The overall prevalence of gallstones was 5.3%. This is not statistically different from the prevalence of gallstones in age-matched groups from previously published studies not selected for country of birth or ethnic background. We found no statistically significant different in prevalence rates for gallstones between Mexican-born and non-Mexican-born pregnant Hispanic women in the 20-year to 49-year age group. Unlike prior studies, this study does not support the use of increased ultrasound examination for cholelithiasis in a pregnant Hispanic population.

MR imaging of the myocardium using nonionic contrast medium: signal-intensity changes in patients with subacute myocardial infarction

OBJECTIVE

Gadodiamide injection (Omniscan, Sanofi Winthrop Pharmaceuticals, New York) is a new nonionic MR contrast medium that has been shown in animal studies to provide persistent differential enhancement of myocardial infarction. Because differential enhancement of normal and infarcted myocardium may be useful for the diagnosis and sizing of myocardial infarctions, we assessed the effectiveness of gadodiamide injection in enhancing signal-intensity differences between infarcted and normal myocardium on spin-echo T1-weighted images.

SUBJECTS AND METHODS

Signal intensity of normal and infarcted myocardium, contrast ratio, contrast-to-noise ratio, and signal-to-noise ratio were measured in 12 patients with subacute myocardial infarction (mean, 16 days after diagnosis) before and after injection of contrast medium. Precontrast T1-weighted and T2-weighted images were obtained with a 1.5-T MR imager. T1-weighted images were acquired 5, 15, and 30 min after gadodiamide injection (0.2 mmol/kg) and T1-weighted images with fat saturation were acquired 10 min after gadodiamide injection.

RESULTS

Gadodiamide injection significantly increased signal intensity of normal (34 +/- %) and infarcted (90 +/- %) myocardium compared with their signal intensities on precontrast T1-weighted images. The contrast ratio was significantly increased, and the augmented ratios persisted throughout the 45-min observation period. The contrast ratio on T2-weighted images was comparable to that on contrast-enhanced T1-weighted images (with or without the use of fat saturation). However, the signal-to-noise and contrast-to-noise ratios of T2-weighted images were significantly lower than those of contrast-enhanced T1-weighted images. The maximum contrast-to-noise ratio for visualizing myocardial infarction was achieved on contrast-enhanced T1-weighted images with fat saturation.

CONCLUSION

Improved and persistent contrast between infarcted and normal myocardium can be produced on MR images by injecting gadodiamide at a dose of 0.2 mmol/kg, which provides prolonged delineation of myocardial infarctions. Maximum contrast-to-noise ratios for detecting myocardial infarction can be produced by using fat-saturated T1-weighted imaging after a high dose of this nonionic contrast medium has been administered.

Paranasal sinuses in pediatric patients by MRI: normal development and preliminary findings in disease

A two-part study using medium field strength magnetic resonance imaging (MRI) was designed to describe the normal paranasal sinus development and to provide preliminary criteria for clinical sinus disease. In part I of the study the paranasal sinuses were retrospectively evaluated in 80 infants and children aged 0-17 years undergoing brain MRI for indications both unrelated and related to sinus disease. We developed MRI criteria for independent grading of paranasal sinus development and 'anatomical' sinus disease, i.e., disease as seen by the radiologist. We quantified the variability in extent of sinus pneumatization (a measure of sinus development) in infants and young children. Part II of the study was a double-blind prospective study in 21 patients to correlate 'anatomical' disease with 'clinical' sinus disease. In this limited preliminary study, clinical sinus disease was only seen in the patients with moderate or severe anatomical disease (sensitivity 100%; specificity 100%).

The pulsatile portal vein in cases of congestive heart failure: correlation of duplex Doppler findings with right atrial pressures

To better understand portal vein pulsatility in congestive heart failure, the authors compared portal vein spectral patterns to right atrial pressures measured with a Swan-Ganz catheter in 17 adult patients suspected of having congestive heart failure. Portal vein pulsatility was also evaluated in 17 healthy adults. A pulsatility score (scale, 1-5) based on a ratio of minimum to peak portal vein velocity was assigned. A score of 1 indicated continuous, monophasic flow, while a score of 5 indicated that flow reversal was observed with each cardiac cycle. All 17 healthy volunteers had portal vein pulsatility scores of 2 or less. Among the 17 patients suspected of having congestive heart failure, seven had normal right atrial pressure (less than 10 mm Hg) and pulsatility scores of 2 or less. Among the 10 patients with a right atrial pressure of 10 mm Hg or greater, six had pulsatility scores of 3 or greater (sensitivity, 60%; specificity, 100%). Greater than 50% of the variation in portal vein score is explained by changes in right atrial pressure. Review of echocardiograms in 13 of 17 patients showed no significant correlation between the degree of tricuspid regurgitation and portal vein score. Portal vein pulsatility is a sign of elevated systemic venous pressure.

Evaluation of renal transplant dysfunction by duplex Doppler sonography: a prospective study and review of the literature

A disconcertingly wide variation exists in the literature as to the accuracy of duplex Doppler sonography in the detection of acute renal transplant rejection. Sensitivities range from 9% to 76%. In an attempt to explain the disparity of results, we undertook a double-blind prospective study of the accuracy of duplex Doppler ultrasound in the detection of acute rejection in renal transplants. We scanned 49 consecutive patients with a total of 65 biopsies; 46 biopsies in 33 consecutive patients were included in our study. In our population, the prevalence of acute rejection was 61% (28/46). Using a resistive index (RI) cutoff of greater than 0.90 based on the main renal artery flow pattern, the sensitivity of our test was 43%, with a 67% specificity. The positive predictive value was 67%. Our results are contrasted and compared with the published data from other groups in a critical survey of the literature. We conclude that duplex Doppler sonography alone is inadequate to evaluate acute rejection in renal transplants.

Color Doppler imaging of portosystemic shunts

This study was designed to investigate the utility of color Doppler sonography in the evaluation of portosystemic shunts. Thirty-one patients with a total of 32 shunts were imaged. The types of shunts examined included portacaval, five; mesocaval, eight; distal splenorenal (Warren), 14; and mesoatrial, five. Sonography was performed without knowledge of the status of the shunt, although the type of shunt was known before beginning the study. The sonographic studies were evaluated to determine their sensitivity and specificity on the basis of a prospective comparison with angiography or MR imaging (22 cases). The possible advantages of color Doppler over duplex Doppler sonography in evaluating portosystemic shunts were also investigated, as was the ability of color Doppler sonography to image specifically the shunt anastomoses. Color Doppler sonography successfully inferred shunt patency (17 cases) or thrombosis (five cases) in all 22 shunts for which correlative imaging was available (sensitivity = 100%, specificity = 100%). In comparing duplex with color Doppler sonography in all 32 shunts, the two techniques were almost equally effective in establishing patency in portacaval, mesocaval, and mesoatrial shunts. Duplex Doppler sonography, however, provided useful diagnostic information in only four of 14 splenorenal shunts. Color Doppler correctly inferred patency or thrombosis in all 14. Among all 32 shunts, the anastomosis was shown clearly by color Doppler in 23, probably in four, and not all in five. Our results suggest that color Doppler sonography is an excellent method for the evaluation of all varieties of surgically created portosystemic shunts. In particular, color Doppler sonography appears to be superior to duplex Doppler sonography in imaging splenorenal communications.

Frequency measurements in real-time US equipment: variations from expected values

The frequency responses of nine real-time mechanical probes and two pulsed Doppler probes from four manufacturers were measured. The reflected frequency was measured in a clinical environment by evaluating the pulser, transducer assembly, and receiver as a system. Two independent systems were used for these measurements: a spectrum analyzer and a data acquisition system that computed the fast Fourier transform of the reflected waveform. Results showed that probe frequency (calibrated by the manufacturer in the transmit mode with a hydrophone) was as much as 30% higher than that found by means of frequency measurement procedures with the probe attached to the ultrasound system and evaluated in the receive mode. Such large discrepancies indicate that if acceptance testing of the frequency spectrum is not performed at a clinical facility, prolonged clinical evaluation of new equipment should be arranged.