Comparison of contrast-enhanced fundamental imaging, second-harmonic imaging, and pulse-inversion harmonic imaging

RATIONALE AND OBJECTIVES: To investigate the feasibility of recent contrast-specific ultrasound techniques in depicting vascular flow and the effects of changing the output power of the transducer and insonation mode on contrast enhancement, the authors performed an experimental study with a flow phantom. METHODS: While changing the mechanical index and the sound insonation mode (continuous and intermittent), images were obtained with three contrast-enhanced ultrasound techniques: fundamental, second-harmonic, and pulse-inversion harmonic imaging (PIHI) after a bolus injection of microbubble contrast agent. The images were compared on a time-intensity curve. RESULTS: In assessing fixed flow (10 cm/s), PIHI showed the best depiction of flow signal. In intermittent scanning, increases in the mechanical index caused stronger flow signals and longer enhancement duration in all techniques. However, continuous scanning revealed poor depiction of flow signal regardless of the technique or changes in the mechanical index because of significant bubble destruction. CONCLUSIONS: Microbubble-enhanced PIHI with intermittent scanning at a high mechanical index can depict vascular flow highly effectively without shortening the duration of enhancement.     

Medical imaging, PACS, and imaging informatics: retrospective

Historical reviews of PACS (picture archiving and communication system) and imaging informatics development from different points of view have been published in the past (Huang in Euro J Radiol 78:163–176, 2011; Lemke in Euro J Radiol 78:177–183, 2011; Inamura and Jong in Euro J Radiol 78:184–189, 2011). This retrospective attempts to look at the topic from a different angle by identifying certain basic medical imaging inventions in the 1960s and 1970s which had conceptually defined basic components of PACS guiding its course of development in the 1980s and 1990s, as well as subsequent imaging informatics research in the 2000s. In medical imaging, the emphasis was on the innovations at Georgetown University in Washington, DC, in the 1960s and 1970s. During the 1980s and 1990s, research and training support from US government agencies and public and private medical imaging manufacturers became available for training of young talents in biomedical physics and for developing the key components required for PACS development. In the 2000s, computer hardware and software as well as communication networks advanced by leaps and bounds, opening the door for medical imaging informatics to flourish. Because many key components required for the PACS operation were developed by the UCLA PACS Team and its collaborative partners in the 1980s, this presentation is centered on that aspect. During this period, substantial collaborative research efforts by many individual teams in the US and in Japan were highlighted. Credits are due particularly to the Pattern Recognition Laboratory at Georgetown University, and the computed radiography (CR) development at the Fuji Electric Corp. in collaboration with Stanford University in the 1970s; the Image Processing Laboratory at UCLA in the 1980s–1990s; as well as the early PACS development at the Hokkaido University, Sapporo, Japan, in the late 1970s, and film scanner and digital radiography developed by Konishiroku Photo Ind. Co. Ltd. (Konica-Minolta), Japan, in the 1980–1990s. Major support from the US National Institutes of Health and other federal agencies and private medical imaging industry are appreciated. The NATO (North Atlantic Treaty Organization) Advanced Study Institute (ASI) sponsored the International PACS Conference at Evian, France, in 1990, the contents and presentations of which convinced a half dozen high-level US military healthcare personnel, including surgeons and radiologists, that PACS was feasible and would greatly streamline the current military healthcare services. The impact of the post-conference summary by these individuals to their superiors opened the doors for long-term support of PACS development by the US Military Healthcare Services. PACS and imaging informatics have thus emerged as a daily clinical necessity.     

Lumbar spine imaging. Normal variants, imaging pitfalls, and artifacts

Accurate recognition and reporting of spine abnormalities on MRI requires knowledge of normal anatomy and its variants. This article deals with common normal variants, points out pitfalls which may be sources of errors in interpretation and describes imaging artifacts which are essential to be recognized and not mistaken for true pathologies.     

Integrated stereotaxic imaging with CT, MR imaging, and digital subtraction angiography

A stereotaxic frame, compatible with digital subtraction angiography, computed tomography, and magnetic resonance imaging, is described along with a set of software programs that run in an independent imaging computer system, as well as in the computers associated with each modality. Plexiglas plates fastened to the sides of the frame contain fiducial markers that can be recognized in the images and from which the section position and in-plane coordinates of any point in the image relative to the frame may be determined. Coordinate measurements of isolated point targets may be made to an accuracy of better than +/- 1 mm within a 15-cm field of view in the plane of the section or projection on all modalities. The stereotaxic system is of sufficiently high accuracy to be used on a routine clinical basis with one or more of the above modalities.     

Gadolinium-enhanced MR imaging, T2-weighted MR imaging, and transurethral ultrasonography

PURPOSE: To assess the value and problems of dynamic gadolinium-enhanced MR imaging, T2-weighted MR imaging, and transurethral ultrasonography(TUUS) in staging of urinary bladder cancer. MATERIALS AND METHODS: Dynamic gadolinium-enhanced MR imaging and FSE T2-weighted MR imaging of 64 patients with urinary bladder cancer who subsequently had surgery were retrospectively reviewed and compared with TUUS findings. RESULTS: Specificity for muscular invasion was 90.5% with TUUS, significantly better than with dynamic MR imaging (64.9%) (p < 0.05). The rates of overestimation of superficial cancer(pT1) with dynamic MRI and T2-weighted MR imaging were 35.1%(13/37) and 24.3%(9/37), respectively. The staging accuracy of invasive cancer(pT2 or over) was 85.2% with dynamic MR imaging, which was better than the rate of 75.0% achieved with T2-weighted MR imaging. CONCLUSION: Although TUUS was a better modality for diagnosing superficial cancer(pT1), dynamic MR imaging was found to be better for diagnosing invasive(pT2 or over) cancer.     

Artifacts, normal variants, and imaging pitfalls of musculoskeletal magnetic resonance imaging

This article is an early attempt to catalogue some of the many artifacts, normal variants, and imaging pitfalls that the authors have seen in musculoskeletal MRI. The study of such phenomena is potentially very rewarding and may help to prevent some cases of misdiagnosis with MRI.     

Classification, diagnostic imaging, and imaging characterization of a lumbar herniated disk

The absence of universal nomenclature standardization with respect to the definition of a disk herniation and its different categories, especially regarding type and location, is still a major problem that will only be overcome when major national or international scientific societies join efforts to support a particular scheme. Meanwhile, it is important to realize that the two models that are currently most used are based on a different [figure: see text] perspective. Trying to straddle the two by opposing, for instance, bulging disk and herniation is doomed to failure because this exercise defies formal logic. MR imaging is currently the most accurate noninvasive imaging modality to diagnose a disk herniation and to determine its exact location. The determination of some pathoanatomic characteristics of herniated disks (type and composition) may require the use of CT, diskography, or CT diskography.     

Cardiac imaging: Part 1, MR pulse sequences, imaging planes, and basic anatomy

OBJECTIVE: MRI is a well-established modality for evaluating congenital and acquired cardiac diseases. This article reviews the latest pulse sequences used for cardiac MRI. In addition, the standard cardiac imaging planes and corresponding anatomy are described and illustrated. CONCLUSION: Familiarity with the basic pulse sequences, imaging planes, and anatomy pertaining to cardiac MRI is essential to formulate optimal protocols and interpretations.     

Coronary magnetic resonance vein imaging: imaging contrast, sequence, and timing.

Recently, there has been increased interest in imaging the coronary vein anatomy to guide interventional cardiovascular procedures such as cardiac resynchronization therapy (CRT), a device therapy for congestive heart failure (CHF). With CRT the lateral wall of the left ventricle is electrically paced using a transvenous coronary sinus lead or surgically placed epicardial lead. Proper transvenous lead placement is facilitated by the knowledge of the coronary vein anatomy. Cardiovascular MR (CMR) has the potential to image the coronary veins. In this study we propose and test CMR techniques and protocols for imaging the coronary venous anatomy. Three aspects of design of imaging sequence were studied: magnetization preparation schemes (T(2) preparation and magnetization transfer), imaging sequences (gradient-echo (GRE) and steady-state free precession (SSFP)), and imaging time during the cardiac cycle. Numerical and in vivo studies both in healthy and CHF subjects were performed to optimize and demonstrate the utility of CMR for coronary vein imaging. Magnetization transfer was superior to T(2) preparation for contrast enhancement. Both GRE and SSFP were viable imaging sequences, although GRE provided more robust results with better contrast. Imaging during the end-systolic quiescent period was preferable as it coincided with the maximum size of the coronary veins.     

Radiological diagnosis of acute stroke. Comparison of conventional MR imaging, echo-planar diffusion-weighted imaging, and spin-echo diffusion-weighted imaging.

PURPOSE: To compare conventional MR imaging, echo-planar diffusion-weighted imaging (EP-DWI) and spin-echo diffusion-weighted imaging (SE)-DWI at radiological diagnosis of acute stroke. MATERIAL AND METHODS: Twenty-seven patients (30-85 years old) were examined. Clinical examination was performed before MR imaging. All MR examinations were assessed by an experienced neuroradiologist blinded to clinical findings. RESULTS: In EP-DWI, every patient had a lesion corresponding to the clinical findings. EP-DWI was used as the gold standard. In conventional PD+T2 imaging, 23/59 focal lesions were interpreted as acute, which was false in 11 lesions, and 36/59 lesions were considered to be old, 6 were in fact acute. Nine acute lesions were only detected retrospectively and 12 acute lesions were not detected at all on PD+T2. SE-DWI including the apparent diffusion coefficient correlated fairly well with EP-DWI but the procedure was impractical. CONCLUSION: EP-DWI is reliable for diagnosis of early ischemic stroke, while SE-DWI performs reasonably well. Conventional PD+T2 imaging is not reliable for diagnosis of early ischemia.     

Diffusion-weighted imaging, apparent diffusion coefficients, and fluid-attenuated inversion recovery MR imaging in endophthalmitis

We describe the appearance of endogenous bacterial endophthalmitis in a patient who underwent MR imaging of the orbits before and during the course of treatment. Intraocular hyperintensity on fluid-attenuated inversion recovery and diffusion-weighted images were found very useful for diagnosing endophthalmitis. After a few days of treatment, a marked relative increase in intraocular mean apparent diffusion coefficient values was observed, which appears to indicate good treatment response.     

Bladder imaging using multidetector row computed tomography,volume rendering,and magnetic resonance imaging

Both multidetector row computed tomography (MDCT) and magnetic resonance imaging (MRI) are used to evaluate the bladder noninvasively. MDCT offers fast imaging with near-isotropic data sets optimized for three-dimensional imaging, including the latest software for volume rendering. MRI provides distinctive soft tissue contrast resolution and can perform dynamic imaging without radiation exposure. This article discusses the techniques and protocols of each modality with case illustrations of their application in a range of bladder pathologies to show their respective distinct advantages and limitations.     

Magnetic resonance imaging of articular cartilage of the knee: comparison between fat-suppressed three-dimensional SPGR imaging, fat-suppressed FSE imaging, and fat-suppressed three-dimensional DEFT imaging, and correlation with arthroscopy

PURPOSE: To compare signal-to-noise ratios (S/N) and contrast-to-noise ratios (C/N) in various MR sequences, including fat-suppressed three-dimensional spoiled gradient-echo (SPGR) imaging, fat-suppressed fast spin echo (FSE) imaging, and fat-suppressed three-dimensional driven equilibrium Fourier transform (DEFT) imaging, and to determine the diagnostic accuracy of these imaging sequences for detecting cartilage lesions in osteoarthritic knees, as compared with arthroscopy. MATERIALS AND METHODS: Two sagittal fat-suppressed FSE images (repetition time [TR] / echo time [TE], 4000/13 [FSE short TE] and 4000/39 [FSE long TE]), sagittal fat-suppressed three-dimensional SPGR images (60/5, 40 degrees flip angle), and sagittal fat-suppressed echo-planar three-dimensional DEFT images (400/21.2) were acquired in 35 knees from 28 patients with osteoarthritis of the knee. The S/N efficiencies (S/Neffs) of cartilage, synovial fluid, muscle, meniscus, bone marrow, and fat tissue, and the C/N efficiencies (C/Neffs) of these structures were calculated. Kappa values, exact agreement, sensitivity, specificity, positive predictive value, and negative predictive value were determined by comparison of MR grading with arthroscopic results. RESULTS: The synovial fluid S/Neff on fat-suppressed FSE short TE images, fat-suppressed FSE long TE images, and fat-suppressed three-dimensional DEFT images showed similar values. Fat-suppressed three-dimensional DEFT images showed the highest fluid-cartilage C/Neff of all sequences. All images showed fair to good agreement with arthroscopy (kappa, 0.615 in FSE short TE, 0.601 in FSE long TE, 0.583 in three-dimensional SPGR, and 0.561 in three-dimensional DEFT). Although the sensitivity of all sequences was high (100% in FSE short TE, FSE long TE, and DEFT; 96.7% in SPGR), specificity was relatively low (67.6% in FSE short TE and FSE long TE; 85.3% in SPGR; 58.3% in DEFT). The peripheral area of bone marrow edema or whole area of bone marrow edema on fat-suppressed FSE images was demonstrated as low or iso-signal intensity on fat-suppressed three-dimensional DEFT images. CONCLUSION: Fat-suppressed three-dimensional SPGR imaging and fat-suppressed FSE imaging showed high sensitivity and high negative predictive values, but relatively low specificity. The Kappa value and exact agreement was the highest on fat-suppressed FSE short TE images. Fat-suppressed three-dimensional DEFT images showed results similar to the conventional sequences.     

Imaging biomarkers, quantitative imaging, and bioengineering

Imaging biomarkers define objective characteristics extracted from medical images that are related to normal biological processes, diseases, or the response to treatment. To develop an imaging biomarker, it is necessary to carry out a series of steps to validate its relation with the reality studied and to check its clinical and technical validity. This process includes defining tests for the concepts and mechanisms; obtaining standardized and optimized anatomic, functional, and molecular images; analyzing the data with computer models; displaying data appropriately; obtaining the appropriate statistic measures; and conducting tests on the principle, efficacy, and effectiveness. In this article, we aim to explain the steps that must be established to enable biomarkers to be correctly applied, from their theoretical conception to their clinical implementation. To this end, we use the evaluation of angiogenesis in articular cartilage as an example.     

Comparison of CT, low-field-strength MR imaging, and high-field-strength MR imaging. Work in progress

To assess objectively the sensitivity and specificity of low-field-strength (0.064 T) magnetic resonance (MR) imaging, a prospective blind study of 280 examinations was performed to compare low-field-strength MR imaging with computed tomography (CT) and with high-field-strength (1.5-T) MR imaging of the cranium. The sensitivity (defined as the true-positive rate) with high-field MR imaging was superior to that with low-field MR imaging and CT in helping detect overall abnormalities. Sensitivities were generally similar over a broad range of specific cranial central nervous system diseases. Low-field and high-field MR imaging were equivalent in the blind diagnoses of neoplasms and white matter disease, whereas low-field MR and CT were equivalent in the blind diagnoses of contusion, subdural and epidural hematoma, sinus disease, normality, and abnormality. The specificities with low-field MR imaging and CT were substantially better than those with high-field MR imaging.     

Subacute sclerosing panencephalitis findings at MR imaging, diffusion MR imaging, and proton MR spectroscopy

A case of subacute sclerosing panencephalitis in a 2-year-old boy is reported. In addition to asymmetric lesions in the parietotemporal lobes, right thalamus, and globus pallidus, symmetric patterns were notable in the brain stem, middle cerebellar pedincles, and dentate nuclei. Proton MR spectroscopy revealed markedly decreased N-acetylaspartate peaks and normal choline and myo-inositol levels in the lesions. Diffusion MR imaging revealed an elevated diffusion pattern manifested with high apparent diffusion coefficient values (1.14-1.60 x 10(-3) mm(2)/s) compared with those in normal-appearing brain tissue (0.65-1.00 x 10(-3) mm(2)/s) and subtle high signal intensity characteristics on diffusion-weighted images obtained at b = 1000 s/mm(2).