PET in cardiology: current status and clinical expectations

Summary. The development of positron emission tomography (PET) in the clinical environment along with the synthesis of biologically active molecules and tracer kinetic principles has provided a diagnostic tool for in vivo tissue characterization in humans. Moreover, based on the growing knowledge of cellular function on the molecular level of diseases PET biological imaging has stimulated the synthesis of numerous metabolic compounds labelled with the four primary positron-emitting radioisotopes C-ll, F-18, N-13 and 0–15. While the concept of biological imaging has gained attraction for probing both the central nervous system and neoplastic tissues, current diagnostic benefit from PET is probably best defined in cardiovascular medicine.     

No regression of renal AL amyloid in monoclonal gammopathy after successful autologous blood stem cell transplantation and significant clinical improvement.

BACKGROUND: High-dose chemotherapy followed by autologous blood stem cell transplantation induces remission of plasma cell dyscrasia in patients with AL amyloidosis. The impact of this treatment on the glomerular amyloid mass is still unknown. METHODS: In the present study, the quantity of the renal amyloid mass before and more than 3 years after high-dose melphalan treatment and autologous blood stem cell transplantation was assessed in two patients. At the time of the second renal biopsy, both patients were in complete remission without detectable serum and urinary monoclonal IgA-lambda and a normal percentage of plasma cells in the bone marrow. RESULTS: In both patients with biopsy-proven AL amyloidosis, urinary protein excretion decreased from 7 g/24 h to <2 g/24 h more than 3 years after autologous blood stem cell transplantation. In contrast, glomerular amyloid deposits persisted, as shown in the second biopsy. CONCLUSION: Despite complete remission of the plasma cell dyscrasia and improvement of glomerular permeability, the amount of glomerular amyloid mass did not regress.     

Method for the quantitative assessment of contrast agent uptake in dynamic contrast-enhanced MRI

In previous papers relative signal intensity increase was used as a quantitative assessment parameter for contrast uptake in contrastenhanced MRI. However, relative signal intensity increase does not only reflect contrast uptake but depends also on tissue parameters (native T₁ relaxation time) and sequence parameters (repetition time and flip angle); thus, the contrast uptake cannot be assessed accurately using relative signal intensity increase. Based on an analysis of the contrast behavior of spoiled gradient echo sequences, a method is described in this paper that overcomes the limitations of relative signal intensity increase measurement. A parameter, called “enhancement factor” (EF) is introduced that approximates differential T₁ relaxation rate. The enhancement factor scales linearly with contrast uptake and is independent of tissue and sequence parameters. The additional measurement time involved in determining the enhancement factor is less than 1 min and computation is straightforward. The practicality of the new method was confirmed by phantom measurements using T₁-weighted and proton density-weighted spoiled gradient echo sequences (FLASH-2D). Enhancing tissues were simulated by water phantoms doped with increasing concentrations of Gd-DTPA.     

Reduced peripheral blood mitochondrial DNA content is not a risk factor for Type 2 diabetes.

AIMS: Mitochondrial depletion in pancreatic beta cells is known to reduce glucose stimulated insulin secretion. We aimed to determine whether the offspring of patients with early onset Type 2 diabetes had reduced peripheral blood mitochondrial content relative to control subjects and whether this could lead to a predisposition to type 2 diabetes in later life. METHODS: We measured the levels of mitochondria relative to a single copy genomic target by real time polymerase chain reaction in a series of peripheral blood samples taken from the offspring of Caucasian patients with Type 2 diabetes and matched controls. Measures of insulin sensitivity and beta cell function were also taken. RESULTS: In contrast with previous studies, mitochondrial DNA content was not decreased in the offspring of patients with Type 2 diabetes relative to matched controls in our cohort. Conversely, we noted a small proliferation in mitochondrial numbers in our case subjects. In agreement with these findings, no correlations with either insulin sensitivity or beta cell function were noted. CONCLUSIONS: Our results indicate that reduced mitochondrial DNA content in peripheral blood is not a risk factor for the development of Type 2 diabetes in the offspring of patients with early onset Type 2 diabetes.     

Quantifying the intra- and extravascular contributions to spin-echo fMRI at 3 T.

Functional MRI (fMRI) by means of spin-echo (SE) techniques provides an interesting alternative to gradient-echo methods because the contrast is based primarily on dynamic averaging associated with the blood oxygenation level-dependent (BOLD) effect. In this article the contributions from different brain compartments to BOLD signal changes in SE echo planar imaging (EPI) are investigated. To gain a better understanding of the underlying mechanisms that cause the fMRI contrast, two experiments are presented: First, the intravascular contribution is decomposed into two fractions with different regimes of flow by means of diffusion-weighting gradient schemes which are either flow-compensated, or will maximally dephase moving spins. Second, contributions from the intra- and extravascular space are selectively suppressed by combining flow-weighting with additional refocusing pulses. The results indicate two qualitatively different components of flowing blood which contribute to the BOLD contrast and a nearly equal share in functional signal from the intra- and extravascular compartments at TE approximately 80 ms and 3 T. Combining these results, there is evidence that at least one-half of the functional signal originates from the parenchyma in SE fMRI at 3 T. The authors suggest the use of flow-compensated diffusion weighting for SE fMRI to improve the sensitivity to the parenchyma.     

法乐四联症右室心肌超微结构定量测量与临床的对比研究

为探讨法乐四联症（Ｆ_４）右室心肌超微结构的不同表现与Ｆ_４术前各项临床检查及术后心功能的关系，作者对室间隔缺损组（Ⅰ组，１１例），儿童Ｆ_４组（Ⅱ组，１３例）和成人Ｆ_４组（Ⅲ组，１３例）进行比较，用Ｓｙｓｔａｔ计算机统计软件作多因素方差分析和Ｐｅａｒｓｏｎ相关研究。结果见Ⅱ、Ⅲ组病人的ＰＯ_２仅和核浆比有关，Ｐ_（ＲＶ）与细胞的核体密度、横径、核浆比及肥大肌细胞比率明显有关，肥大肌细胞比率与病人年龄及ＰａＯ_２明显相关。作者认为Ｆ_４病人右室心肌超微结构改变主要系右室压力增高所致，这种改变与年龄有关。     

Quantification of in-plane motion of the coronary arteries during the cardiac cycle: Implications for acquisition window duration for MR flow quantification

Motion of the coronary arteries during the heart cycle can result in image blurring and inaccurate flow quantification by MR. This condition applies particularly for longer acquisition windows that are typical of breath-hold coronary flow measurements. To determine the sensitivity of the technique to in-plane motion of different coronary arteries, the temporal variation in coronary position was measured in a plane perpendicular to the proximal portion of the vessel. The results indicated the presence of substantial displacement of the coronary arteries within the cardiac cycle, with a magnitude of motion approximately twice as large for the right as for the left coronary arteries. An estimation of the resulting vessel blurring was calculated, showing that the duration of the acquisition window for high spatial resolution coronary flow acquisitions should be less than 25 to 120 msec, depending on the specific coronary artery studied. In addition, these data specify optimal acquisition window placement for high resolution coronary angiography.     

The use of a priori knowledge to quantify short echo in vivo 1h mr spectra

In vivo ¹H MR spectra of the prefrontal cortex acquired with the stimulated echo acquisition mode (STEAM) TE = 20 ms sequence were quantified to determine relative levels of cerebral metabolites. A priori knowledge of spectra from individual metabolites in aqueous solution was incorporated into a frequency domain quantification technique. The accuracy and precision of modeling these metabolites were investigated with simulated spectra of varying signal-to-noise ratios (SNRs) and relative metabolite levels. The efficacy of modeling in vivo data was tested by quantifying 10 repeated measures of two consecutively acquired in vivo spectra (an 8?cm³ volume of interest (VOI) and a 4?cm³ VOI positioned within the 8?cm³ VOI) on the same normal subject. The differences in levels of glutamate (Glu), phosphocreatine plus creatine (PCr+Cr) and choline-containing compounds (Cho₁ between spectra from the 8? and 4?cm³ VOIs corresponded with the expected differences observed in the proportions of gray matter within the VOIs (estimated from ¹H images). Correcting for the T₁ and T₂ relaxation, the estimated concentrations of N-acetylaspartate, PCr+Cr, Cho₁, Glu, and glutamine were consistent with previous in vivo and in vitro reports.