Information and artifact in computed tomography image statistics.

In conventional computed tomography images only the average CT number, which is a first-order statistical parameter, is used to characterize the tissues by giving an estimate of tissue density. Second order statistical parameters such as the signal variance and cross-correlation function have also been used to obtain additional information to discriminate between certain tissues and lesions. However, the contribution of quantum noise to the signal variance and cross-correlation function creates, for the conventional CT patient dose, a background signal often larger than the signal containing the information about tissue structure. The misleading information, called "artifacts", in second-order image statistics caused by quantum noise, is studied.

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.

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.

MR angiography of the 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. Coronary arteries are small, tortuous vessels subjected to significant physiological motions (respiration and cardiac contractions). Most coronary MRA pulse sequences rely on a combination of segmental acquisition of data (in k-space) to minimize cardiac motion artifacts and patient breath-holding to minimize respiratory motion artifacts. MR is noninvasive, does not require any contrast agents or ionizing radiation, and thus offers the potential of becoming a very important cardiac screening tool. Coronary MRA can routinely depict the proximal and middle portion of most coronary arteries and some coronary artery branches. However, its clinical utility for detecting lesions has not yet been proven. As coronary MRA techniques improve they may become an integral part of the evaluation of patients with ischemic heart disease. Existing coronary MRA techniques can already play a significant clinical role in the evaluation of coronary artery anomalies, in the follow-up of proximal lesions after angioplasty, and in the noninvasive determination of patency of bypass grafts and coronary stents.

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.

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.

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%).

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.

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.

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.

Estimation of acoustic attenuation in liver using one megabyte of data and the zero-crossings technique.

Statistical fluctuations due to scatter-induced frequency variations in reflected acoustic pulses are a major problem when estimating acoustic attenuation. Disagreement exists in the ultrasound community as to how much data is sufficient to overcome these statistical fluctuations. The range of attenuation values for normal livers and a tissue equivalent phantom, using 1 megabyte of data per liver and the zero-crossings technique, was investigated. The significance of statistical fluctuations and their effects on attenuation are discussed.

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.

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.

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.