Klaus D. Hagspiel

MRI of the lungs using hyperpolarized noble gases

The nuclear spin polarization of the noble gas isotopes 3He and 129Xe can be increased using optical pumping methods by four to five orders of magnitude. This extraordinary gain in polarization translates directly into a gain in signal strength for MRI. The new technology of hyperpolarized (HP) gas MRI holds enormous potential for enhancing sensitivity and contrast in pulmonary imaging. This review outlines the physics underlying the optical pumping process, imaging strategies coping with the nonequilibrium polarization, and effects of the alveolar microstructure on relaxation and diffusion of the noble gases. It presents recent progress in HP gas MRI and applications ranging from MR microscopy of airspaces to imaging pulmonary function in patients and suggests potential directions for future developments. Magn Reson Med 47:1029–1051, 2002.

Gastrointestinal and Hepatic Manifestations of Sarcoidosis

Sarcoidosis is a multisystem disease characterized by noncaseating granulomas in the affected organs, including skin, heart, nervous system, and joints. Diagnosis of sarcoidosis is generally based upon a compatible history, demonstration of granulomas in at least two different organs, negative staining and culture for acid fast bacilli, absence of occupational or domestic exposure to toxins, and lack of drug-induced disease. Involvement of the hollow organs is rare. Rather than being due to sarcoidosis, some reported mucosal lesions may simply have incidental granulomas. Extrinsic compression from lymphadenopathy can occur throughout the gastrointestinal tract. The stomach, particularly the antrum, is the most common extrahepatic organ to be involved, while the small bowel is the least common. Liver involvement frequently occurs and ranges from asymptomatic incidental granulomas to portal hypertension from granulomas in the portal triad, usually with relatively preserved liver function. CT scans show hepatosplenomegaly and adenopathy, followed in frequency by focal low-attenuation lesions of the liver and spleen. Ascites is usually a transudate from right heart failure (because of pulmonary hypertension) or portal hypertension (because of biliary cirrhosis). Rarely, an exudative ascites may occur from studding of the peritoneum with nodules. Pancreatic involvement presents as a mass, usually in the head or a diffusely firm, nodular organ. Corticosteroids should be instituted when organ function is threatened, usually lungs, eyes, and central nervous system. Their role in the treatment of hepatic sarcoidosis is unclear. The overall prognosis is good although most patients will have some permanent organ impairment. Cardiac and pulmonary diseases are the main causes of death.

Probing lung physiology with xenon polarization transfer contrast (XTC)

One of the major goals of hyperpolarized‐gas MRI has been to obtain 129Xe dissolved‐phase images in humans. So far, this goal has remained elusive, mainly due to the low concentration of xenon that dissolves in tissue. A method is proposed and demonstrated in dogs that allows information about the dissolved phase to be obtained by imaging the gas phase following the application of a series of RF pulses that selectively destroy the longitudinal magnetization of xenon dissolved in the lung parenchyma. During the delay time between consecutive RF pulses, the depolarized xenon rapidly exchanges with the gas phase, thus lowering the gas polarization. It is demonstrated that the resulting contrast in the 129Xe gas image provides information about the local tissue density. It is further argued that minor pulse‐sequence modifications may provide information about the alveolar surface area or lung perfusion. Magn Reson Med 44:349–357, 2000.

Ultrasound-accelerated Thrombolysis for the Treatment of Deep Vein Thrombosis: Initial Clinical Experience

PURPOSE To evaluate the success of lysis and clinical outcomes in patients treated with ultrasound (US)-accelerated thrombolysis for deep vein thrombosis (DVT). MATERIALS AND METHODS Forty-seven patients with 53 cases of DVT were treated with US-accelerated thrombolysis at eight centers in the United States. Sixty percent of the occlusions were in the lower extremity, 36% were in the upper extremity, and 4% were hepatic. The clot was acute (< or =14 days) in 47% of cases, subacute (15-28 d) in 8%, chronic (>28 d) in 17%, acute-on-chronic in 17%, and not specified in 11%. Patients were treated with urokinase (UK), tissue plasminogen activator (tPA), recombinant plasminogen activator (rPA), or tenecteplase. RESULTS Complete lysis (> or =90%) was seen in 37 of 53 cases (70%) and overall lysis (complete plus partial) was seen in 48 (91%). No lysis occurred in five cases (9%), four of which were chronic. The median thrombolysis infusion time was 22.0 hours. Major complications (hematoma at site of earlier surgery) occurred in only two patients (3.8%), with no incidence of intracranial or retroperitoneal hemorrhage. US-accelerated thrombolysis exhibited comparable or better lysis with a lower average drug dose and shorter median treatment times than reported in the National Venous Registry and a more recently published study of standard catheter-directed thrombolysis. CONCLUSIONS US-accelerated thrombolysis was shown to be a safe and efficacious treatment for DVT in this multicenter experience. The addition of US reduces total infusion time and provides a greater incidence of complete lysis with a reduction in bleeding rates.

Percutaneous transluminal angioplasty and stenting in the treatment of chronic mesenteric ischemia: results and longterm followup

BACKGROUND The purpose of this study was to review the results of percutaneous transluminal angioplasty (PTA), stenting, or both in the treatment of patients who present with symptoms and angiographic findings most consistent with chronic mesenteric ischemia. STUDY DESIGN A retrospective analysis of 33 consecutive patients from a single institution who underwent PTA, stenting, or both for treatment of symptoms most characteristic of chronic mesenteric ischemia was performed. RESULTS There were 12 men and 21 women with a mean age of 63 years (range 40 to 89 years). Median weight loss was 28 lb (range 6 to 80 lb). Postprandial pain was present in 88% of the patients (29 of 33). All lesions treated were stenoses. PTA alone was performed in 21 patients (32 vessels), and PTA and stenting were performed in 12 patients (15 vessels). PTA was technically successful in 26 of 32 vessels (81.3%); PTA plus stenting was technically successful in 15 of 15 vessels (100%) (p = 0.073). Complete alleviation of symptoms occurred immediately in 27 of the patients (82%), and 2 patients (6%) had significant improvement in symptoms. There were four immediate clinical failures (12%): two patients were found to have occult malignancy and one had immediate relief of symptoms after surgical release of the median arcuate ligament. Followup data were obtained in all patients with clinically successful procedures (mean 38 months, median 25 months, range 1 to 123 months). Angiographic followup was available in 52% of the patients (15 of 29), at a mean of 20 months. The primary longterm clinical success rate was 83.3% (24 of 29). Four of the five patients with recurrent symptoms were successfully retreated with endovascular therapy. The primary assisted longterm clinical success rate was 96.6% (28 of 29). The 5-year survival rate was 76.1%. Major complications occurred in 13% of the procedures, with a 30-day mortality rate of 0%. CONCLUSION Endovascular therapy for treatment of mesenteric arterial stenoses is effective in the treatment of patients with symptoms and angiographic findings characteristic of chronic mesenteric ischemia.

Magnetic resonance imaging identifies the fibrous cap in atherosclerotic abdominal aortic aneurysm.

Background—MRI can distinguish components of atherosclerotic plaque. We hypothesized that contrast enhancement with gadolinium-DTPA (Gd-DTPA) could aid in the differentiation of plaque components in abdominal aortic aneurysm (AAA). Methods and Results—Twenty-three patients (19 males, age 70±8 years) with AAA underwent MRI on a 1.5-T clinical scanner 3±3 days before surgical grafting. T1- and T2-weighted (W) black blood spin echo imaging was performed in 1 axial slice, and the T1-W imaging was repeated after a Gd-DTPA–enhanced 3D magnetic resonance angiogram. A section of the aorta at the site of imaging was resected at surgery for histopathologic examination of tissue components and inflammatory cells. Signal-to-noise and contrast-to-noise ratios (CNR) were measured in visualized plaque components from multispectral MRI, and percent enhancement after contrast on T1-W imaging was calculated. The &kgr; value for agreement between pathology and MRI for the number of tissue components was 0.785. T2-W imaging identified thrombus as regions of high signal and lipid core as low signal, with a CNR of 6.43±3.41. Nine patients had a fibrous cap pathologically, which was visualized as a discrete area of uniform increased signal on T2-W imaging with a CNR of 4.52±1.93 compared with lipid core. Within the cap, the percent enhancement after Gd-DTPA on T1-W imaging was 91±63%. Conclusions—Higher signal on T2-W MRI identifies the fibrous cap and thrombus within AAA. Contrast enhancement improves delineation of the fibrous cap. The addition of contrast to MRI plaque imaging may enhance identification of vulnerable plaque.

MR imaging of soft-tissue vascular malformations: diagnosis, classification, and therapy follow-up.

Vascular malformations and tumors comprise a wide, heterogeneous spectrum of lesions that often represent a diagnostic and therapeutic challenge. Frequent use of an inaccurate nomenclature has led to considerable confusion. Since the treatment strategy depends on the type of vascular anomaly, correct diagnosis and classification are crucial. Magnetic resonance (MR) imaging is the most valuable modality for classification of vascular anomalies because it accurately demonstrates their extension and their anatomic relationship to adjacent structures. A comprehensive assessment of vascular anomalies requires functional analysis of the involved vessels. Dynamic time-resolved contrast material-enhanced MR angiography provides information about the hemodynamics of vascular anomalies and allows differentiation of high-flow and low-flow vascular malformations. Furthermore, MR imaging is useful in assessment of treatment success and establishment of a long-term management strategy. Radiologists should be familiar with the clinical and MR imaging features that aid in diagnosis of vascular anomalies and their proper classification. Furthermore, they should be familiar with MR imaging protocols optimized for evaluation of vascular anomalies and with their posttreatment appearances. Supplemental material available at http://radiographics.rsna.org/lookup/suppl/doi:10.1148/rg.315105213/-/DC1.

CTA and MRA in Mesenteric Ischemia: Part 1, Role in Diagnosis and Differential Diagnosis

OBJECTIVE CT angiography and MR angiography are the main techniques for the noninvasive diagnosis of mesenteric ischemia. High clinical suspicion and knowledge of the differential diagnostic possibilities in this clinical setting are essential for the correct interpretation of the scans. CONCLUSION CT angiography and MR angiography are well suited for the workup of patients when mesenteric ischemia is suspected.

Exploring lung function with hyperpolarized 129Xe nuclear magnetic resonance

With the use of polarization‐transfer pulse sequences and hyperpolarized 129Xe NMR, gas exchange in the lung can be measured quantitatively. However, harnessing the inherently high sensitivity of this technique as a tool for exploring lung function requires a fundamental understanding of the xenon gas‐exchange and diffusion processes in the lung, and how these may differ between healthy and pathological conditions. Toward this goal, we employed NMR spectroscopy and imaging techniques in animal models to investigate the dependence of the relative xenon gas exchange rate on the inflation level of the lung and the tissue density. The spectroscopic results indicate that gas exchange occurs on a time scale of milliseconds, with an average effective diffusion constant of about 3.3 × 10−6cm2/s in the lung parenchyma. Polarization‐transfer imaging pulse sequences, which were optimized based on the spectroscopic results, detected regionally increased gas‐exchange rates in the lung, indicative of increased tissue density secondary to gravitational compression. By exploiting the gas‐exchange process in the lung to encode physiologic parameters, these methods may be extended to noninvasive regional assessments of lung‐tissue density and the alveolar surface‐to‐volume ratio, and allow lung pathology to be detected at an earlier stage than is currently possible. Magn Reson Med 51:676–687, 2004.

Carotid Artery Calcification on CT May Independently Predict Stroke Risk

OBJECTIVE The purpose of our study was to quantitatively evaluate calcified atherosclerotic burden in the cervical carotid arteries using MDCT to determine the relationship of scores with luminal stenosis and symptomatology. MATERIALS AND METHODS Calcium plaque volume was measured in 106 cervical carotid arteries (53 patients) using MDCT angiography. The study group included 32 asymptomatic patients (mean age, 70.2 +/- 8.7 [SD] years; 15 women, 17 men) and 21 patients with ischemic neurologic symptoms (69.6 +/- 12.9 years; eight women, 13 men). By vessel, there were 43 high-grade stenotic (> or = 60% by North American Symptomatic Carotid Endarterectomy Trial [NASCET] criteria), 15 moderate-grade stenotic (30-59%), and 44 mild-grade stenotic or normal (0-29%) vessels, with four excluded for prior carotid endarterectomy. Volume scores were calculated by summing the area of calcium in the common and extracranial internal carotid arteries on axial slices and multiplying by the slice increment. RESULTS Controlling for cardiovascular risk factors and luminal stenosis, we found that scores were significantly related to the occurrence of symptoms (p = 0.003). Even with patient age as a covariant, patients with high-grade stenosis had significantly higher scores than those without high-grade disease (p = 0.004). Moreover, quantitative burden was associated with luminal stenosis on adjusted multivariate analysis (p = 0.034). The specificity and positive predictive value for high-grade luminal narrowing were notably lower on individual vessel analysis than on total score analysis, likely secondary to variability in vascular remodeling. CONCLUSION Calcium scores in the cervical carotid arteries may represent an independent marker for luminal stenosis and ischemic symptoms. A prospective longitudinal study examining calcium levels and morbidity may be warranted to examine whether burden has a role in risk stratification.