Coronary artery calcium assessment on non-gated chest CT to optimize pre-operative cardiac screening in liver transplantation

BACKGROUND

Guidelines recommend standard pre-operative cardiac screening in all liver transplantation (LT) recipients, despite the relatively low prevalence of obstructive coronary artery disease. Most LT recipients often have non-gated computed tomography (CT) performed of the chest and abdomen. This study evaluated the ability of coronary artery calcification (CAC) assessment on consecutively available scans, to identify a selection of low-risk patients, in whom further cardiac imaging can be safely withheld.

METHODS

LT recipients with prior non-gated CT chest-abdomen were included. CAC was visually scored on a semi-quantitative ordinal scale. Stress myocardial perfusion, coronary CT angiography (CCTA) and invasive coronary angiography (ICA) were used as golden standard. The sensitivity and specificity of CAC to exclude and predict obstructive CAD were assessed. In addition, peri- and postoperative mortality and cardiac events were analyzed.

RESULTS

149 LT recipients (ranged 31-71 years) were included. In 75% of patients, no CAC and mild CAC could rule out obstructive CAD on CCTA and ICA with 100% certainty. The threshold of mild CAC had a sensitivity of 100% for both CCTA and ICA and a specificity of 91% and 68%, respectively. None of the patients with no or mild calcifications experienced peri- and post-operative cardiac events or died of cardiac causes.

CONCLUSION

Visual evaluation of CAC on prior non-gated CT can accurately and safely exclude obstructive CAD in LT recipients. Incorporation of these already available data can optimize cardiac screening, by safely withholding or correctly allocating dedicated cardiac imaging in LT recipients. Thereby, reducing patients' test burden and save health care expenses.

Importance of complete response for outcomes of pregnancy in patients with autoimmune hepatitis

BACKGROUND AND AIMS

While some articles describe outcome of pregnancy in autoimmune hepatitis (AIH), there are less data evaluating influence of AIH control on maternal and perinatal outcomes. This study analysed outcomes of pregnancy and related possible risk factors in AIH.

METHOD

A retrospective multicentre cohort study on pregnancy in AIH was performed in 11 hospitals in the Netherlands. Maternal and neonatal outcomes were collected from records and completed by interview. Risk factors-including incomplete response, relapse and cirrhosis-for adverse outcomes were identified using logistic regression analysis.

RESULTS

Ninety-seven pregnancies in 50 women resulted in 70 deliveries (72%) with a live birth rate of 98.5%. AIH relapse occurred in 6% during pregnancy, and in 27% of post-partum episodes. Absence of complete biochemical response at conception was identified as risk factor for the occurrence of gestational and post-partum relapses. Relapse of AIH in the year before conception was a risk factor for the occurrence of both gestational relapses and post-partum relapses. No complete biochemical response increased the risk for hypertensive disorders during pregnancy and intrahepatic cholestasis of pregnancy (ICP). Cirrhosis was found to be a risk factor for miscarriages, but not for other outcomes.

CONCLUSION

Pregnancy in AIH is related to an increased incidence of maternal and fetal/neonatal complications; in most cases, outcome is good. Incomplete biochemical response at conception or relapse in the year before conception are risk factors for gestational and post-partum relapses, for hypertensive disorders and for ICP. Cirrhosis was a risk factor for miscarriages.

Protease inhibitors partially overcome the interferon nonresponse phenotype in patients with chronic hepatitis C

The outcome of triple therapy with protease inhibitors (PI) depends on the intrinsic response to interferon. Interferon-stimulated gene (ISG) expression differs by cell type in the liver and is a strong predictor of interferon responsiveness. Patients who respond well to interferon have low/absent ISG expression in hepatocytes but significant ISG expression in macrophages. Nonresponders (NRs) show the opposite pattern. We aimed to determine the association between cell-type-specific ISG staining and treatment outcome with PI-based triple therapy. Liver biopsy tissue from consecutive patients treated with boceprevir or telaprevir with peginterferon and ribavirin was stained for myxovirus A (MxA). Staining was scored 0-3 in macrophages (M-MxA) and hepatocytes (H-MxA), and IL28B genotyping was performed. Of 56 patients included 41 achieved SVR (73%) (sustained virological response), 2 (4%) relapsed, 10 (18%) were NRs, and 3 (5%) were lost to follow-up. Median M-MxA staining was stronger and H-MxA staining was weaker in patients who achieved SVR. MxA staining correlated with IL28B genotype and with the HCV RNA decline during lead-in phase. However, unlike with dual therapy, the negative predictive value (NPV) of absent or weak M-MxA staining was poor (42%), while the positive predictive value improved (93%). Although by multivariable logistic regression M-MxA staining was significantly associated with SVR (OR 4.35, 1.32-14.28, P = 0.012), the predictive ability was inadequate to withhold therapy. The interaction between macrophages and hepatocytes plays a critical role in interferon responsiveness; however, the addition of a PI at least partially overcomes the interferon nonresponse phenotype making the predictive ability of ISG staining less clinically useful.

Three-dimensional characterization of resorption cavity size and location in human vertebral trabecular bone

The number and size of resorption cavities in cancellous bone are believed to influence rates of bone loss, local tissue stress and strain and potentially whole bone strength. Traditional two-dimensional approaches to measuring resorption cavities in cancellous bone report the percent of the bone surface covered by cavities or osteoclasts, but cannot measure cavity number or size. Here we use three-dimensional imaging (voxel size 0.7×0.7×5.0 μm) to characterize resorption cavity location, number and size in human vertebral cancellous bone from nine elderly donors (7 male, 2 female, ages 47-80 years). Cavities were 30.10 ± 8.56 μm in maximum depth, 80.60 ± 22.23∗10(3) μm(2) in surface area and 614.16 ± 311.93∗10(3) μm(3) in volume (mean ± SD). The average number of cavities per unit tissue volume (N.Cv/TV) was 1.25 ± 0.77 mm(-3). The ratio of maximum cavity depth to local trabecular thickness was 30.46 ± 7.03% and maximum cavity depth was greater on thicker trabeculae (p<0.05, r(2)=0.14). Half of the resorption cavities were located entirely on nodes (the intersection of two or more trabeculae) within the trabecular structure. Cavities that were not entirely on nodes were predominately on plate-like trabeculae oriented in the cranial-caudal (longitudinal) direction. Cavities on plate-like trabeculae were larger in maximum cavity depth, cavity surface area and cavity volume than cavities on rod-like trabeculae (p<0.05). We conclude from these findings that cavity size and location are related to local trabecular microarchitecture.

Mechanical failure begins preferentially near resorption cavities in human vertebral cancellous bone under compression

The amount of bone turnover in the body has been implicated as a factor that can influence fracture risk and bone strength. Here we test the idea that remodeling cavities promote local tissue failure by determining if microscopic tissue damage (microdamage) caused by controlled loading in vitro is more likely to form near resorption cavities. Specimens of human vertebral cancellous bone (L4, 7 male and 2 female, age 70±10, mean±SD) were loaded in compression to the yield point, stained for microscopic tissue damage and submitted to three-dimensional fluorescent imaging using serial milling (image voxel size 0.7×0.7×5.0 μm). We found the resulting damage volume per bone volume (DV/BV) was correlated with percent eroded surface (p<0.01, r(2)=0.65), demonstrating that whole specimen measures of resorption cavities and microdamage are related. Locations of microdamage were more than two times as likely to have a neighboring resorption cavity than randomly selected sites without microdamage (relative risk 2.39, 95% confidence interval of relative risk: 2.09-2.73), indicating a spatial association between resorption cavities and microdamage at the local level. Individual microdamage sites were 48,700 (40,100; 62,700) μm(3) in size (median, 25th and 75th percentiles). That microdamage was associated with resorption cavities when measured at the whole specimen level as well as at the local level provides strong evidence that resorption cavities play a role in mechanical failure processes of cancellous bone and therefore have the potential to influence resistance to clinical fracture.

Liver allograft pathology: approach to interpretation of needle biopsies with clinicopathological correlation

The spectrum of diseases encountered in post-transplant liver pathology biopsies is broad. In this review, these have been divided as belonging to one of three categories: (1) new-onset/de novo post-transplant abnormalities (early and late), (2) rejection, and (3) recurrence of original disease. The clinical and pathological features of the entities making up each category, with the relevant differential diagnosis and overlaps between and within these groups, are discussed and illustrated. Recurrent or de novo neoplasms make up a fourth category not included in this review. Early new-onset conditions are mostly related to surgical complications, donor factors and ischaemia to the graft. These include reperfusion/preservation injury, lipopeliosis, small-for-size-syndrome, biliary sludge syndrome and hepatic artery thrombosis. The various forms of rejection (cellular, chronic, antibody-mediated, and late atypical rejection) are detailed. Most chronic liver diseases can and do recur in the graft. They may display features that overlap with de novo conditions (eg, primary sclerosing cholangitis versus chronic rejection). As with most cases of allograft biopsy interpretation, accurate diagnosis rests with careful correlation of histological features with clinical, imaging and laboratory findings, and often comparison with previous sequential and follow-up biopsies. Late-onset new diseases include biliary strictures, idiopathic chronic hepatitis and de novo autoimmune hepatitis, among others. This review provides a practical approach to the interpretation of these challenging biopsies. Selected difficult scenarios or conundrums are identified and discussed in the relevant sections.

Liver allograft pathology: approach to interpretation of needle biopsies with clinicopathological correlation

The spectrum of diseases encountered in post-transplant liver pathology biopsies is broad. In this review, these have been divided as belonging to one of three categories: (1) new-onset/de novo post-transplant abnormalities (early and late), (2) rejection, and (3) recurrence of original disease. The clinical and pathological features of the entities making up each category, with the relevant differential diagnosis and overlaps between and within these groups, are discussed and illustrated. Recurrent or de novo neoplasms make up a fourth category not included in this review. Early new-onset conditions are mostly related to surgical complications, donor factors and ischaemia to the graft. These include reperfusion/preservation injury, lipopeliosis, small-for-size-syndrome, biliary sludge syndrome and hepatic artery thrombosis. The various forms of rejection (cellular, chronic, antibody-mediated, and late atypical rejection) are detailed. Most chronic liver diseases can and do recur in the graft. They may display features that overlap with de novo conditions (eg, primary sclerosing cholangitis versus chronic rejection). As with most cases of allograft biopsy interpretation, accurate diagnosis rests with careful correlation of histological features with clinical, imaging and laboratory findings, and often comparison with previous sequential and follow-up biopsies. Late-onset new diseases include biliary strictures, idiopathic chronic hepatitis and de novo autoimmune hepatitis, among others. This review provides a practical approach to the interpretation of these challenging biopsies. Selected difficult scenarios or conundrums are identified and discussed in the relevant sections.

Gastric mucin is expressed in a subset of endocervical tunnel clusters: type A tunnel clusters of gastric phenotype

AIMS

Gastric mucin expression has been demonstrated in a group of endocervical glandular lesions. The aim of this study was to gain further insight into endocervical lesions with a gastric phenotype.

METHODS AND RESULTS

Various types of tunnel clusters (TC) were examined for gastric mucin by alcian blue/periodic acid-Schiff staining and immunohistochemistry for HIK1083. Five of 34 cases of TC expressed gastric mucin defined by PAS dominant neutral mucin and immunopositivity for pyloric gland mucin. Histologically, TC expressing gastric mucin showed lobular arrangements of small to medium-sized glands composed of mucin-rich columnar cells and were classified as Flumann's type A TC. Neither type B TC nor normal endocervical glands expressed PAS dominant neutral mucin and none of them was immunopositive for pyloric gland mucin. Five patients with type A TC of gastric phenotype ranged in age from 33 to 79 years (mean 58 years) and were multiparous. Type A TC of gastric phenotype, ranging from 2 to 4 mm in maximum diameter, were incidental findings in hysterectomy specimens.

CONCLUSION

Type A TC of gastric phenotype could be related to lobular endocervical glandular hyperplasia of gastric phenotype. The pathogenesis of gastric metaplasia in TC remains unclear.

Quantifying effects of retinal illuminance on frequency doubling perimetry

PURPOSE

To measure and quantify effects of variation in retinal illuminance on frequency doubling technology (FDT) perimetry.

METHODS

A Zeiss-Humphrey/Welch Allyn FDT perimeter was used with the threshold N-30 strategy. Study 1, quantifying adaptation: 11 eyes of 11 subjects (24-46 years old) were tested with natural pupils, and then retested after stable pupillary dilation with neutral density filters of 0.0, 0.6, 1.2, and 1.6 log unit in front of the subject's eye. Study 2, predicting effect of reduced illuminance: 17 eyes of 17 subjects (26-61 years old) were tested with natural pupils, and then retested after stable pupillary miosis (assessed with an infrared camera). A quantitative adaptation model was fit to results of Study 1; the mean adaptation parameter was used to predict change in Study 2.

RESULTS

Study 1: Mean defect (MD) decreased by 10 dB over a 1.6 log unit range of retinal illuminances; model fits for all subjects had r2> 95%. Study 2: Change in MD (DeltaMD) ranged from -7.3 dB to +0.8 dB. The mean adaptation parameter from Study 1 accounted for 69% of the variance in DeltaMD (P <0.0005), and accuracy of the model was independent of the magnitude of DeltaMD (r2< 1%, P >0.75).

CONCLUSIONS

The results confirmed previous findings that FDT perimetry can be dramatically affected by variations in retinal illuminance. Application of a quantitative adaptation model provided guidelines for estimating effects of pupil diameter and lens density on FDT perimetry.

High-resolution magnetic resonance coronary angiography of the entire heart using a new blood-pool agent, NC100150 injection: comparison with invasive x-ray angiography in pigs

Recent developments of novel magnetic resonance intravascular contrast agents with low T1 in blood and a long intravascular half-life will rapidly position magnetic resonance coronary angiography (MRCA) at the threshold of clinical application. This article describes the use of one such intravascular contrast agent for noninvasive coronary angiography and comparison with routine invasive x-ray angiography. Six domestic farm pigs with an artificial stenoses at the left circumflex were studied. NC100150 Injection, a new ultra-small superparmagnetic iron oxide (Nycomed Amersham Imaging, Oslo, Norway), was injected using a dose of 5.0 mg Fe/kg body weight. Scanning was done using a 1.5-T Gyroscan ACS-NT. A high-resolution electrocardiogram-triggered scan covering the entire heart was applied. Navigator echoes were used for respiratory triggering. In all animals the location of the stenoses detected with MRCA correlated well with x-ray angiography. The correlation factor between the grade of stenoses determined by MRCA and x-ray angiography was 0.993. MRCA using NC100150 Injection can depict the major coronary arteries and branches well. Decreases in vessel caliber detected by MRCA correlate well with x-ray angiography. The use of such intravascular contrast agents show great promise for clinical applications for noninvasive detection of coronary artery disease in humans.

Dicer functions in RNA interference and in synthesis of small RNA involved in developmental timing in C. elegans

Double-stranded RNAs can suppress expression of homologous genes through an evolutionarily conserved process named RNA interference (RNAi) or post-transcriptional gene silencing (PTGS). One mechanism underlying silencing is degradation of target mRNAs by an RNP complex, which contains approximately 22 nt of siRNAs as guides to substrate selection. A bidentate nuclease called Dicer has been implicated as the protein responsible for siRNA production. Here we characterize the Caenorhabditis elegans ortholog of Dicer (K12H4.8; dcr-1) in vivo and in vitro. dcr-1 mutants show a defect in RNAi. Furthermore, a combination of phenotypic abnormalities and RNA analysis suggests a role for dcr-1 in a regulatory pathway comprised of small temporal RNA (let-7) and its target (e.g., lin-41).

Regulated transposition of a fish transposon in the mouse germ line

Tc1/mariner elements are able to transpose in species other than the host from which they were isolated. As potential vectors for insertional mutagenesis and transgenesis of the mouse, these cut-and-paste transposons were tested for their ability to transpose in the mouse germ line. First, the levels of activity of several Tc1/mariner elements in mammalian cells were compared; the reconstructed fish transposon Sleeping Beauty (SB) was found to be an order of magnitude more efficient than the other tested transposons. SB then was introduced into the mouse germ line as a two-component system: one transgene for the expression of the transposase in the male germ line and a second transgene carrying a modified transposon. In 20% of the progeny of double transgenic male mice the transposon had jumped from the original chromosomal position into another locus. Analysis of the integration sites shows that these jumps indeed occurred through the action of SB transposase, and that SB has a strong preference for intrachromosomal transposition. Analysis of the excision sites suggests that double-strand breaks in haploid spermatids are repaired via nonhomologous end joining. The SB system may be a powerful tool for transposon mutagenesis of the mouse germ line.

Measurement of the gadopentetate dimeglumine partition coefficient in human myocardium in vivo: normal distribution and elevation in acute and chronic infarction

PURPOSE

To establish a method for measuring the partition coefficient (lambda) of gadopentetate dimeglumine in humans in vivo, evaluate the spatial and intersubject variation in the lambda of normal myocardium, and compare these values on a regional basis with lambda values of acute and chronic infarcted myocardium.

MATERIALS AND METHODS

Twelve healthy subjects and patients with acute (n = 5) or chronic (n = 5) myocardial infarction underwent magnetic resonance imaging at 1.5 T. Look-Locker images were acquired at four short-axis levels to measure myocardial and blood longitudinal relaxation time at baseline and after a 30-40-minute infusion of gadopentetate dimeglumine. lambda was calculated as DeltaR1(M)/DeltaR1(B, )where M = myocardium, and B = blood.

RESULTS

The magnitude of the estimated lambda in normal myocardium was uniform over the entire myocardium at 0.56 mL/g +/- 0.10 (SD). The lambda values in patients with acute (0.91 mL/g +/- 0.11, P <.001) or chronic (lambda = 0.78 mL/g +/- 0.09, P <.001) infarction were significantly elevated, as compared with those in healthy subjects. A 20% elevation in lambda, as compared with the mean value of a corresponding normal circumferential segment, allowed identification of chronically (sensitivity, 88%; specificity, 96%) or acutely (sensitivity, 100%; specificity, 98%) infarcted segments.

CONCLUSION

Quantification of the lambda in vivo allows differentiation between normal and acutely or chronically infarcted myocardium, with high sensitivity and specificity.

Performance of QRS detection for cardiac magnetic resonance imaging with a novel vectorcardiographic triggering method

In many cardiac patients, image quality and/or scan efficiency is reduced due to imprecise R-wave ability to trigger the scan due to noise on the electrocardiogram (ECG) caused by the magnetic resonance (MR) environment. We developed a triggering system that uses the spatial information of the vectorcardiogram (VCG) to minimize the effects of MR-related noise on triggering. Fifteen volunteers underwent standard cardiovascular MR exams, and a total of 52,474 R-waves were evaluated with the algorithm, giving a performance index of 99.91%. The mean propagation delay of the system was -10.64 +/- 3.19 msec, which falls within the real-time definition for cardiac MRI triggering. Five patients had arrhythmias consisting of premature ventricular depolarizations (PVDs) and supraventricular extra systoles. For those patients with PVDs, all arrhythmic beats were rejected unless they passed through the algorithm's reference point. The performance index for the arrhythmic patients approached 100%. VCG-based triggering has been demonstrated to provide near 100% triggering performance during cardiac MR examinations.

Quantification of left ventricular function with magnetic resonance images acquired in real time

The application of real-time magnetic resonance imaging (MRI) techniques to cardiac imaging is particularly attractive because current MR examinations of left ventricular (LV) function can be prohibitively long and are dependent on electrocardiographic triggering. We conducted a study of the minimum spatial and temporal resolution requirements necessary for real-time ventricular function MR imaging to quantify LV volumes accurately, both at resting conditions and during cardiac stress tests. In addition, we implemented a real-time segmented echoplanar imaging pulse sequence and used it to quantify LV volume in 10 healthy volunteers. We compared these results with those obtained using conventional gradient-echo cine imaging and found good agreement throughout the cardiac cycle (mean difference -0.8 +/- 10.6 ml). In conclusion, real-time cardiac MR imaging can be used to quantify LV volumes accurately throughout the cardiac cycle, over the physiologic range of heart rates, thereby decreasing the time required for a complete functional cardiac examination. J. Magn. Reson. Imaging 2000;12:430-438.

Noninvasive modalities. Cardiac MR imaging

As outlined in this article, the strength of MR imaging is that it can provide flow, function, and in some cases metabolic data in a single examination, independent of patient body habitus. Future prospects for real-time imaging and in vivo mapping of fiber orientation promise further advances in our understanding of the structure-function relationship in diastole. Many of the MR imaging methods that have been developed for cardiovascular imaging are now mature and available on state-of-the-art scanners. Although MR imaging can provide detailed characterization of diastolic function, there is a paucity of clinical results which could lead to use guidelines. When more clinicians have access and become familiar with MR imaging, and the type of information that it can provide, clinical trials will be needed to establish the role of MR imaging for evaluation of diastolic function. In the meantime, MR imaging remains an excellent research tool for this application and will help yield further insights into the pathophysiology of diastolic dysfunction.

Left ventricular contractility is impaired following myocardial infarction in the pig and rat: assessment by the end systolic pressure-volume relation using a single-beat estimation technique and cine magnetic resonance imaging

The end systolic pressure-volume relation (ESPVR) has been shown to be a relatively load independent measure of left ventricular (LV) contractility. Recently, several single-beat ESPVR computation methods have been developed, enabling the quantification of LV contractility without the need to alter vascular loading conditions on the heart. Using a single-beat ESPVR method, which has been validated previously in humans and assumes that normalized elastance is constant between individuals of a species, we studied the effects of myocardial infarction on LV contractility in two species, the rat and the pig. In our studies, LV pressure was acquired invasively and LV volume determined noninvasively with magnetic resonance imaging, at one week postinfarction in pigs and at 12 weeks postinfarction in rats. Normalized systolic elastance curves in both animal species were not statistically different from that of humans. Also, the slope of the ESPVR (Ees) decreased significantly following infarction in both species, while the volume-axis intercept (V0) was unaffected. These results indicate that a single-beat ESPVR method can be used to measure the inotropic response of the heart to myocardial infarction, and that the basis for this method (i.e., constant normalized elastance) is applicable to a variety of mammalian species.

Cardiac rotation and relaxation in patients with aortic valve stenosis

BACKGROUND

Diastolic dysfunction with delayed relaxation and abnormal passive elastic properties has been described in patients with severe pressure overload hypertrophy. The purpose of this study was to evaluate the time course of rotational motion of the left ventricle in patients with aortic valve stenosis using myocardial tagging.

METHODS

Myocardial tagging is a non-invasive method based on magnetic resonance which makes it possible to label ('tag') specific myocardial regions. From the motion of the tag's cardiac rotation, radial displacement and translational motion can be determined. In 12 controls and 13 patients with severe aortic valve stenosis systolic and diastolic wall motion was assessed in an apical and basal short axis plane.

RESULTS

The normal left ventricle performs a systolic wringing motion around the ventricular long axis with clockwise rotation at the base (-4.4+/-1.6 degrees) and counter-clockwise rotation at the apex (+6.8+/-2.5 degrees) when viewed from the apex. During early diastole an untwisting motion can be observed which precedes diastolic filling. In patients with aortic valve stenosis systolic rotation is reduced at the base (-2.4+/-2.0 degrees; P<0.01) but increased at the apex (+12.0+/-6.0 degrees; P<0.05). Diastolic untwisting is delayed and prolonged with a decrease in normalized rotation velocity (-6.9+/-1.1 s(-1)) when compared to controls (-10.7+/-2.2 s(-1); P<0.001). Maximal systolic torsion is 8.0+/-2.1 degrees in controls and 14.1+/-6.4 degrees (P<0.01) in patients with aortic valve stenosis.

CONCLUSIONS

Left ventricular pressure overload hypertrophy is associated with a reduction in basal and an increase in apical rotation resulting in increased torsion of the ventricle. Diastolic untwisting is delayed and prolonged. This may explain the occurrence of diastolic dysfunction in patients with severe pressure overload hypertrophy.

Single breath-hold slice-following CSPAMM myocardial tagging

Myocardial tagging has shown to be a useful magnetic resonance modality for the assessment and quantification of local myocardial function. Many myocardial tagging techniques suffer from a rapid fading of the tags, restricting their application mainly to systolic phases of the cardiac cycle. However, left ventricular diastolic dysfunction has been increasingly appreciated as a major cause of heart failure. Subtraction based slice-following CSPAMM myocardial tagging has shown to overcome limitations such as fading of the tags. Remaining impediments to this technique, however, are extensive scanning times (approximately 10 min), the requirement of repeated breath-holds using a coached breathing pattern, and the enhanced sensitivity to artifacts related to poor patient compliance or inconsistent depths of end-expiratory breath-holds. We therefore propose a combination of slice-following CSPAMM myocardial tagging with a segmented EPI imaging sequence. Together with an optimized RF excitation scheme, this enables to acquire as many as 20 systolic and diastolic grid-tagged images per cardiac cycle with a high tagging contrast during a short period of sustained respiration.

Cis requirements for transposition of Tc1-like transposons in C. elegans

The Caenorhabditis elegans transposons Tc1 and Tc3 are able to transpose in heterologous systems such as human cell lines and zebrafish. Because these transposons might be useful vectors for transgenesis and mutagenesis of diverse species, we determined the minimal cis requirements for transposition. Deletion mapping of the transposon ends shows that fewer than 100 bp are sufficient for transposition of Tc3. Unlike Tc1, Tc3 has a second, internal transposase binding site at each transposon end. We found that these binding sites play no major role in the transposition reaction, since they can be deleted without reduction of the transposition frequency. Site-directed mutagenesis was performed on the conserved terminal base pairs at the Tc3 ends. The four terminal base pairs at the ends of the Tc3 inverted repeats were shown to be required for efficient transposition. Finally, increasing the length of the transposon from 1.9 kb to 12.5 kb reduced the transposition frequency by 20-fold, both in vivo and in vitro.

Novel real-time R-wave detection algorithm based on the vectorcardiogram for accurate gated magnetic resonance acquisitions

Electrocardiograph (ECG) triggered or gated magnetic resonance methods are used in many imaging applications. Therefore, a reliable trigger signal derived from to the R-wave of the ECG is essential, especially in cardiac imaging. However, currently available methods often fail mainly due to the artifacts in the ECG generated by the MR scanner itself, such as the magnetohydrodynamic effect and gradient switching noise. The purpose this study was to characterize the accuracy of selected R-wave detection algorithms in an MR environment, and to develop novel approaches to eliminate imprecise triggering. Vectorcardiograms (VCG) in 12 healthy volunteers exposed to 1.5 T magnetic field were digitized and used as a reference data set including manually corrected onsets of R-waves. To define the magnetohydrodynamic effect, the VCGs were characterized in time, frequency, and spatial domains. The selected real-time R-wave detection algorithms, and a new "target-distance" VCG-based algorithm were applied either to standard surface leads calculated from the recorded VCG or to the VCG directly. The flow related artifact was higher in amplitude than the R-wave in 28% of the investigated VCGs which yielded up to 9-16%false positive detected QRS complexes for traditional algorithms. The "target-distance" R-wave detection algorithm yielded a score of 100% for detection with 0.2% false positives and was superior to all the other selected methods. Thus, the VCG of subjects exposed to a strong magnetic field can be use to separate the magnetohydrodynamic artifact and the actual R-wave, and markedly improves the trigger accuracy in gated magnetic resonance scans. Magn Reson Med 42:361-370, 1999.

Alterations in the local myocardial motion pattern in patients suffering from pressure overload due to aortic stenosis

BACKGROUND

MR tissue tagging allows the noninvasive assessment of the locally and temporally resolved motion pattern of the left ventricle. Alterations in cardiac torsion and diastolic relaxation of the left ventricle were studied in patients with aortic stenosis and were compared with those of healthy control subjects and championship rowers with physiological volume-overload hypertrophy.

METHODS AND RESULTS

Twelve aortic stenosis patients, 11 healthy control subjects with normal left ventricular function, and 11 world-championship rowers were investigated for systolic and diastolic heart wall motion on a basal and an apical level of the myocardium. Systolic torsion and untwisting during diastole were examined by use of a novel tagging technique (CSPAMM) that provides access to systolic and diastolic motion data. In the healthy heart, the left ventricle performs a systolic wringing motion, with a counterclockwise rotation at the apex and a clockwise rotation at the base. Apical untwisting precedes diastolic filling. In the athlete's heart, torsion and untwisting remain unchanged compared with those of the control subjects. In aortic stenosis patients, torsion is significantly increased and diastolic apical untwisting is prolonged compared with those of control subjects or athletes.

CONCLUSIONS

Torsional behavior as observed in pressure- and volume-overloaded hearts is consistent with current theoretical findings. A delayed diastolic untwisting in the pressure-overloaded hearts of the patients may contribute to a tendency toward diastolic dysfunction.

Benefit of T1 reduction for magnetic resonance coronary angiography: a numerical simulation and phantom study

Contrast agents have dramatically improved magnetic resonance angiography (MRA) of the abdominal and peripheral arteries. The imaging technique for these applications is usually a steady-state acquisition, for which the relationship between T1 in blood and the MR signal is well known. However, in electrocardiography-triggered angiography with limited acquisition windows, this relationship is more complex. Therefore the purpose of this work is to define the relationship between the T1 in blood and the MR signal amplitude in three-dimensional magnetic resonance coronary angiography (3D-MRCA). Simulations were performed using equations describing the MR signal in both steady-state and triggered acquisition schemes. Triggered acquisition schemes use flip-angle sweeps to maintain a constant signal during the acquisition. In this study, the effect of the flip angle sweep was calculated as a function of T1. The results show that the effect of T1 shortening in contrast-enhanced 3D-MRCA differs substantially from that in conventional contrast-enhanced MRA. The triggered acquisition allows unsaturated blood to enter the volume between the acquisitions and thereby gives a much higher signal at long T1s than does steady-state acquisition. Therefore, to gain a benefit in signal amplitude with contrast agents for 3D-MRCA using gradient-echo sequences, the T1 in blood may have to be as low as 50 msec. In addition, when using a prepulse to null myocardium, the results indicate the need for a large difference in T1 between blood and myocardium to avoid signal loss in blood.

Toward high-resolution myocardial tagging

Magnetic resonance imaging with preceding tissue tagging is a robust method for assessing cardiac motion of the entire heartbeat cycle with a high degree of accuracy. One limitation of this technique, however, is the low resolution of the obtained displacement map of the labeled points within the myocardium. By a new tagging technique, which is based on the combination of two or more measurements of the same slice but with different grid positions, a highly improved resolution of cardiac motion data can be achieved. In combination with a multi-heart-phase echo-planar imaging sequence, such images with doubled grid frequency can be acquired in two short breath-hold periods.

Blood pool agent strongly improves 3D magnetic resonance coronary angiography using an inversion pre-pulse

The ability of a blood pool contrast agent to enhance MR coronary angiography was defined. The proximal coronary vessels of pigs were imaged before and after administration of Gd-DTPA bound covalently to bovine serum albumin (0.2 mmol/ kg). The contrast agent resulted in a reduction of the blood T1 value to 33+/-5 msec, as determined in vivo with a Look-Locker technique. Both 2D and 3D imaging techniques were performed. An inversion pulse suppressed the signal of nonblood tissue postcontrast. After contrast agent administration, in the 3D data set the signal-to-noise ratio (SNR) of blood and contrast-to-noise ratio (CNR) of blood to myocardium were improved by factors of 2.0+/-0.2 and 15+/-8, respectively (P < 0.05). Postcontrast, the 3D acquisition was superior to the 2D technique in terms of spatial resolution, SNR of blood, and CNR of blood to myocardium. The high contrast of the 3D data set allowed for direct and rapid display of coronary arteries using a "closest vessel projection."

Quantification of the local heartwall motion by magnetic resonance myocardial tagging

Sophisticated magnetic resonance tagging techniques provide powerful tools for the non-invasive assessment of the local heartwall motion towards a deeper fundamental understanding of local heart function. For the extraction of motion data from the time series of magnetic resonance tagged images and for the visualization of the local heartwall motion a new image analysis procedure has been developed. New parameters have been derived which allows quantification of the motion patterns and are highly sensitive to any changes in these patterns. The new procedure has been applied for heart motion analysis in healthy volunteers and in patient collectives with different heart diseases. The achieved results are summarized and discussed.

Effect of prolonged dissociation on the subjective measurement of near heterophoria

Previous studies have demonstrated that vergence adaptation resulting from the prolonged decay of slow fusional vergence may prevent the accurate assessment of oculomotor deviations. Continuing changes in heterophoria have been reported after 27 days of monocular occlusion. However, since most slow fusional vergence will decay within the first few minutes of dissociation, a clinical assessment of both vergence adaptation and heterophoria could be made more rapidly. This report documents two investigations which examined changes in near horizontal heterophoria during 30 min and 180 min of continuous dissociation, respectively. Seven out of the 16 subjects exhibited significant changes in heterophoria during the 30 min dissociation period, with a mean increase in exophoria of 3.4 delta. The decay of slow fusional vergence took approximately 25 min to reach completion. Thus in the clinical setting, both the degree of vergence adaptation and a more accurate assessment of heterophoria may be obtained by maintaining dissociation for 25 min. Furthermore, the presence of vergence adaptation can be assessed after just 5 min of dissociation.

Target choice determinants of the Tc1 transposon of Caenorhabditis elegans

The Tc1 transposon of Caenorhabditis elegans always integrates into the sequence TA, but some TA sites are preferred to others. We investigated a TA target site from the gpa-2 gene of C.elegans that was previously found to be preferred (hot) for Tc1 integration in vivo . This site with its immediate flanks was cloned into a plasmid, and remained hot in vitro , showing that sequences immediately adjacent to the TA dinucleotide determine this target choice. Further deletion mapping and mutagenesis showed that a 4 bp sequence on one side of the TA is sufficient to make a site hot; this sequence nicely fits the previously identified Tc1 consensus sequence for integration. In addition, we found a second type of hot site: this site is only preferred for integration when the target DNA is supercoiled, not when it is relaxed. Excision frequencies were relatively independent of the flanking sequences. The distribution of Tc1 insertions into a plasmid was similar when we used nuclear extracts or purified Tc1 transposase in vitro , showing that the Tc1 transposase is the protein responsible for the target choice.

[Determining heart muscle perfusion by magnetic resonance tomography progressing to clinical application]

Magnetic resonance imaging detects the flow of contrast-enhanced blood and even allows the quantitative assessment of myocardial perfusion. The clinical application of this method is being held back by the difficulties in image evaluation and the limitation of standard techniques to the acquisition of a single slice per heart beat cycle. Recent developments in scanner hardware as well as in image acquisition techniques open up the possibility of assessing myocardial perfusion over the entire heart with a spatial resolution in the range of 2 mm. As an example of such a new scanning strategy, a segmented gradient-echo recalled echo planar imaging sequence with preceding saturation is discussed and results in a patient with an infarction are presented. The clinical use of perfusion assessment covering the entire heart for the diagnosis of coronary artery disease is enhanced by the flexibility of magnetic resonance imaging for the assessment of functional cardiac parameters.

High-frequency ultrasonic detection of thrombi with a targeted contrast system

Site-targeted acoustic contrast agents used in conjunction with high-frequency intravascular ultrasound have the potential to localize and characterize intravascular pathology. The present study quantifies the utility of a novel, site-targeted ultrasonic contrast agent with high-frequency ultrasound (30 to 50 MHz) and demonstrates the feasibility of the new agent for augmenting detection of targeted pathology with intravascular ultrasonic catheters. High-frequency acoustic microscopy was used to image avidinconjugated nitrocellulose membranes after exposure to a control or biotinylated contrast agent. Increases (p < 0.05) in backscattered power of approximately 66 dB (4-fold) were found for the biotinylated, but not the control contrast agent. Intravascular ultrasonic images (30 MHz nominal center frequency) of plasma clots after exposure to the targeted contrast agent were brighter (p < 0.05) than in controls. These results demonstrate high-frequency acoustic enhancement with a novel targeted contrast agent and may extend the potential diagnostic spectrum of intravascular ultrasound.

Massive intracranial immature teratoma. Report of a case with polyhidramnios and intense pelvic pain

A case of massive intracranial immature teratoma in a female stillborn is reported. She was the product of the second pregnancy of a 25-year-old healthy woman. The pregnancy was unremarkable until the 25th week of gestation when the mother noticed a rapid enlargement of her abdomen and intense pelvic pain. Because of the pain, a cesarean section was indicated, and a stillborn weighing 2750g with macrocephaly was delivered. The cranial contents weighed 1350g and showed a huge tumoral mass with only a rim of normal brain. A histologic diagnosis of immature teratoma was made. Massive intracranial teratomas are rare tumors and their occurrence in intrauterine life is even rarer. Their histogenesis is unknown, and there is no explanation for their continuous growth during embryogenesis. A prenatal diagnosis of this rare condition can be made by ultrasound, computed tomography, or magnetic resonance imaging.

Limitations of stimulated echo acquisition mode (STEAM) techniques in cardiac applications

Stimulated echoes are widely used for imaging functional tissue parameters such as diffusion coefficient, perfusion, and flow rates. They are potentially interesting for the assessment of various cardiac functions. However, severe limitations of the stimulated echo acquisition mode occur, which are related to the special dynamic properties of the beating heart and flowing blood. To the well-known signal decay due to longitudinal relaxation and through-plane motion between the preparation and the read-out period of the stimulated echoes, additional signal loss is often observed. As the prepared magnetization is fixed with respect to the tissue, this signal loss is caused by the tissue deformation during the cardiac cycle, which leads to a modification of the modulation frequency of the magnetization. These effects are theoretically derived and corroborated by phantom and in vivo experiments.

Real-time image reconstruction system for interventional magnetic resonance surgery

Interventional surgery techniques under the control of fast acquired magnetic resonance (MR) images may become important in interventional radiology in the near future. One of the components needed for an interventional MR scanner is the real-time reconstruction of the acquired MR images. However up to now no real-time reconstruction systems are readily available for MR images. Therefore a reconstruction device was developed, which allows reconstruction and display of MR images with a delay of less than 50 ms. Additional to the high performance, the main characteristics of the presented device are its full compatibility with different MR acquisition techniques and its moderate cost. The device can be operated with most types of commercial scanners. It is especially suited for interventional MR systems but has also applications with conventional MR scanners.

True myocardial motion tracking

Myocardial tagging is a powerful tool for the assessment of in-plane cardiac motion. However, for previous myocardial tagging techniques, the imaged slice is fixed with respect to the magnet coordinate system. Thus, images acquired at different heart phases do not always represent the same slice of the myocardium. A new myocardial tagging technique is presented, which takes the through-plane motion into consideration. It involves tagging of the desired myocardial slice and applying a subtraction imaging technique to image just that part of the myocardium. The examination time can be reduced considerably by the acquisition of two one-dimensionally tagged images. To increase the signal-to-noise ratio especially at later heart phases, variable imaging RF excitation flip angles are applied. To reduce motion artifacts a repetitive breathhold scheme was applied. In vivo results demonstrate that the tags can be accurately tracked within the entire heart period with a temporal resolution of 35 ms, even at a top basal level of the heart and right ventricle.

Improved myocardial tagging contrast

Myocardial tagging is a new noninvasive MRI method that allows the study of myocardial motion with high accuracy. However, with conventional tagging techniques tagging contrast is impaired at later heart phases due to longitudinal relaxation. An improved method, called Complementary SPAtial Modulation of Magnetization (CSPAMM), which separates the component of the magnetization with the tagging information from the relaxed component by subtraction of two measurements with first a positive and then a negative tagging grid, is presented. This technique improves the grid contrast and greatly facilitates the automatic evaluation of the myocardial motion. Thus the motion assessment of the entire heart cycle becomes possible. The improvements are documented by numerical simulations and by experiments on phantoms and on human volunteers.

Evaluation of left ventricular segmental wall motion in hypertrophic cardiomyopathy with myocardial tagging

BACKGROUND

Segmental wall motion was assessed noninvasively in eight patients with hypertrophic cardiomyopathy and six healthy volunteers by magnetic resonance myocardial tagging.

METHODS AND RESULTS

Localization scans were performed for determination of the true short-axis views of the left ventricle (double-angulated view). Spatial modulation of magnetization was used to produce a rectangular grid of landmarks. Distortion of the grid was assessed at end diastole, mid systole, and end systole with multiphase gradient echoes. Image sets were acquired at three different planes, namely, the base, the equator, and the apex. Quantitative evaluation was carried out by computer-assisted image analysis. Each individual grid crossing point was identified automatically and the displacement calculated. A polar coordinate system with the center of gravity as motion reference point was chosen to assess fractional rotation and radial displacement at the endocardial, midwall, and epicardial layers of the septal, anterior, posterior, and inferior regions. A wringing motion of the left ventricle with a clockwise rotation of 5.0 +/- 2.4 degrees at the base and a counterclockwise rotation of -9.6 +/- 2.9 degrees at the apex was observed in control subjects. An equal rotation of 5.0 +/- 2.5 degrees at the base and a slightly reduced rotation of -7.3 +/- 5.2 degrees at the apex was found in patients with hypertrophic cardiomyopathy. A transmural gradient in fractional rotation and radial displacement was observed, with the highest values in the endocardial layer. Rotation in patients with hypertrophic cardiomyopathy was significantly less than in normal volunteers in the posterior region of the equatorial and apical planes. Furthermore, radial displacement was significantly reduced in the septum and inferior wall. In the anterior and posterior wall segments, a reduction of the radial displacement was observed only in the epicardium and midwall layers.

CONCLUSIONS

Magnetic resonance myocardial tagging allows the noninvasive assessment of regional wall motion. Both in normal volunteers and in patients with hypertrophic cardiomyopathies, cardiac motion occurs in a complex mode, with the base and the apex rotating in opposite directions and the equatorial plane as a transitional zone (wringing motion). A reduced cardiac rotation can be observed in patients with hypertrophic cardiomyopathy mainly in the posterior region, whereas a reduced radial displacement is found in the inferior septal zone.

Acquisition and evaluation of tagged magnetic resonance images of the human left ventricle

Magnetic resonance myocardial tagging was used to noninvasively analyze the complicated contraction pattern of the human cardiac left ventricle. The tagging and imaging sequence was optimized to obtain three to four double-angulated short-axis views during systole. The image contrast between labeled and unlabeled tissue was sufficient to apply a semiautomatic image evaluation procedure. In accordance with the invasively achieved findings of other groups, the measurements indicate a wringing motion of the left ventricle, with a clockwise twist at the heartbase and a contrary rotation at the apical level.

Non invasive measurement of myocardial motion using magnetic resonance tagging

Magnetic resonance imaging has become a key modality within the modern radiology department. In addition to the conventional slice images, three dimensional angiographic images, and quantitative flow measurements can be obtained. More recently methods have been developed which enable one to visualize the motion of objects through the application of magnetic resonance markers or tags. Generally the myocardium appears homogeneous with respect to magnetic resonance imaging. Thus at best the displacement of the myocardial surfaces can be observed, but rotational and shear motions are not discernable. With magnetic resonance tagging this all changing. Tagging involves modifying the ability of the tissue to produce a nuclear magnetic resonance signal, in a spatially dependent manner. Typically the pattern is a grid of reduced signal intensity. The tagging grid is applied prior to the heart contraction. Then images are made during systole and diastole. The rotation and shear of the myocardium can be inferred from the distortions of the tagging grid. Here our work in this field is reviewed.