Correlation of functional MR imaging activation data with simple reaction times

PURPOSE: To determine the relationship between subject reaction times (RTs) and activation volume in the brain during visuomotor functional magnetic resonance (MR) imaging. MATERIALS AND METHODS: Twenty-four subjects performed a simple RT task during single-event functional MR imaging, and RTs were recorded. The six subjects with the fastest RTs were designated the fast RT group, and the six subjects with the slowest RTs were designated the slow RT group. The data were processed with noncorrected height threshold (P <.001) for individual comparisons and corrected height threshold (P <.05) for group comparisons (t tests). The activation volumes in both occipital lobes, the left sensorimotor cortex, and the supplemental motor cortices were compared for the two groups. RESULTS: The mean RT +/- SD was 342 msec +/- 20.15 for the fast RT group and 475 msec +/- 36.17 for the slow RT group (P <.0001). More voxels of activation were seen in the fast RT group than in the slow RT group in the occipital lobes, left sensorimotor cortices, and supplemental motor cortices on individual and group maps. This difference was statistically significant in the left sensorimotor (P =.03) and left visual (P =.05) cortices. In the right visual cortex, a trend toward more activation in the fast RT group was noted (P =.15). There was a negative correlation between RTs and activation volume in the left sensorimotor cortex (P =.048). CONCLUSION: There was a greater activation volume in motor and visual cortices in the fast RT group than in the slow RT group.     

Nonlinear changes in brain activity during continuous word repetition: an event-related multiparametric functional MR imaging study

BACKGROUND AND PURPOSE: Changes in brain activation as a function of continuous multiparametric word recognition have not been studied before by using functional MR imaging (fMRI), to our knowledge. Our aim was to identify linear changes in brain activation and, what is more interesting, nonlinear changes in brain activation as a function of extended word repetition. MATERIALS AND METHODS: Fifteen healthy young right-handed individuals participated in this study. An event-related extended continuous word-recognition task with 30 target words was used to study the parametric effect of word recognition on brain activation. Word-recognition-related brain activation was studied as a function of 9 word repetitions. fMRI data were analyzed with a general linear model with regressors for linearly changing signal intensity and nonlinearly changing signal intensity, according to group average reaction time (RT) and individual RTs. RESULTS: A network generally associated with episodic memory recognition showed either constant or linearly decreasing brain activation as a function of word repetition. Furthermore, both anterior and posterior cingulate cortices and the left middle frontal gyrus followed the nonlinear curve of the group RT, whereas the anterior cingulate cortex was also associated with individual RT. CONCLUSION: Linear alteration in brain activation as a function of word repetition explained most changes in blood oxygen level-dependent signal intensity. Using a hierarchically orthogonalized model, we found evidence for nonlinear activation associated with both group and individual RTs.     

Reproducibility of functional MR imaging: preliminary results of prospective multi-institutional study performed by Biomedical Informatics Research Network

PURPOSE: To prospectively investigate the factors--including subject, brain hemisphere, study site, field strength, imaging unit vendor, imaging run, and examination visit--affecting the reproducibility of functional magnetic resonance (MR) imaging activations based on a repeated sensory-motor (SM) task. MATERIALS AND METHODS: The institutional review boards of all participating sites approved this HIPAA-compliant study. All subjects gave informed consent. Functional MR imaging data were repeatedly acquired from five healthy men aged 20-29 years who performed the same SM task at 10 sites. Five 1.5-T MR imaging units, four 3.0-T units, and one 4.0-T unit were used. The subjects performed bilateral finger tapping on button boxes with a 3-Hz audio cue and a reversing checkerboard. In a block design, 15-second epochs of alternating baseline and tasks yielded 85 acquisitions per run. Functional MR images were acquired with block-design echo-planar or spiral gradient-echo sequences. Brain activation maps standardized in a unit-sphere for the left and right hemispheres of each subject were constructed. Areas under the receiver operating characteristic curve, intraclass correlation coefficients, multiple regression analysis, and paired Student t tests were used for statistical analyses. RESULTS: Significant factors were subject (P < .005), k-space (P < .005), and field strength (P = .02) for sensitivity and subject (P = .03) and k-space (P = .05) for specificity. At 1.5-T MR imaging, mean sensitivities ranged from 7% to 32% and mean specificities were higher than 99%. At 3.0 T, mean sensitivities and specificities ranged from 42% to 85% and from 96% to 99%, respectively. At 4.0 T, mean sensitivities and specificities ranged from 41% to 73% and from 95% to 99%, respectively. Mean areas under the receiver operating characteristic curve (+/- their standard errors) were 0.77 +/- 0.05 at 1.5 T, 0.90 +/- 0.09 at 3.0 T, and 0.95 +/- 0.02 at 4.0 T, with significant differences between the 1.5- and 3.0-T examinations and between the 1.5- and 4.0-T examinations (P < .01 for both comparisons). Intraclass correlation coefficients ranged from 0.49 to 0.71. CONCLUSION: MR imaging at 3.0- and 4.0-T yielded higher reproducibility across sites and significantly better results than 1.5-T imaging. The effects of subject, k-space, and field strength on examination reproducibility were significant.     

Hemodynamic response changes in cerebrovascular disease: implications for functional MR imaging

BACKGROUND AND PURPOSE: Patients with cerebrovascular occlusive disease may develop compensatory changes in local cerebral vasculature with a resultant loss of vascular reactivity. These alterations can affect the blood oxygen level-dependent (BOLD) signal that is the basis for functional MR imaging. We investigated the BOLD signal in patients with unilateral cerebrovascular disease to ascertain the clinical utility of functional MR imaging in these patients. METHODS: Five healthy volunteers and three patients with cerebro-occlusive disease were imaged with both a block and an event-related design of a visually cued bilateral motor task. Activation maps were calculated, and individual hemodynamic response curves were generated for left and right primary motor cortices. Vascular reserve was determined for the relevant vascular territory by using transcranial Doppler ultrasonography (US). RESULTS: In the event-related data, the amplitude of the BOLD response was significantly decreased in the motor cortex ipsilateral to the stenosis and showed significant delays in the timing of the hemodynamic response. In contrast, the longer duration stimulus and longer TR of the block design showed significant decreases in the BOLD amplitude but no significant interhemispheric temporal differences. Corroborating the hemodynamic status, transcranial Doppler US analysis showed diminished vascular reserve ipsilateral to the lesion. CONCLUSION: Differences in the results between the event-related and block paradigms reflect the sensitivity to alterations in autoregulation or vascular compliance. These changes in the vasculature directly affect the BOLD contrast underlying functional MR imaging. Thus, while this technique remains a useful clinical tool, caution is warranted when studying patients with cerebrovascular disease.     

Primary intracranial atypical teratoid/rhabdoid tumors of infancy and childhood: MRI features and patient outcomes

BACKGROUND AND PURPOSE: Primary atypical teratoid/rhabdoid tumors (AT/RTs) are rare malignant intracranial neoplasms, usually occurring in young children. The objectives of this study were to characterize the MR imaging features and locations of primary intracranial AT/RTs, to determine the frequency of disseminated disease in the central nervous system (CNS) at diagnosis and postoperatively, and to assess patient outcomes. METHODS: The preoperative cranial MR images of 13 patients with AT/RTs were retrospectively reviewed for evaluation of lesion location, size, MR signal intensity and enhancement characteristics, and the presence of disseminated intracranial tumor. Postoperative MR images of the head and spine for 17 patients were reviewed for the presence of locally recurrent or residual tumor and disseminated neoplasm. Imaging data were correlated with patient outcomes. RESULTS: Patients ranged in age from 4 months to 15 years (median age, 2.9 years). Primary AT/RTs were intra-axial in 94% of patients. The single primary extra-axial lesion was located in the cerebellopontine angle cistern. AT/RTs were infratentorial in 47%, supratentorial in 41%, and both infra- and supratentorial in 12%. A germ-line mutation of the hSNF5/INI1 tumor-suppressor gene was responsible for the simultaneous occurrence of an intracranial AT/RT and a malignant renal rhabdoid tumor in a 4-month-old patient. Mean tumor sizes were 3.6 x 3.8 x 3.9 cm. On short TR images, AT/RTs typically had heterogeneous intermediate signal intensity, as well as zones of low (54%), high (8%), or both low and high (31%) signal intensity from cystic and/or necrotic regions, hemorrhage, or both, respectively. On long TR/long TE images, solid portions of AT/RTs typically had heterogeneous intermediate-to-slightly-high signal intensity with additional zones of high (54%) or both high and low signal intensity (38%), secondary to cystic and/or necrotic regions, edema, prior hemorrhage, and/or calcifications. AT/RT had isointense and/or slightly hyperintense signal intensity relative to gray matter on fluid-attenuated inversion-recovery (FLAIR) and long TR/long TE images, and showed restricted diffusion. All except 1 AT/RT showed contrast enhancement. The fraction of tumor volume showing enhancement was greater than two thirds in 58%, between one third and two thirds in 33%, and less than one third in 9%. Disseminated tumor in the leptomeninges was seen with MR imaging in 24% of patients at diagnosis/initial staging and occurred in another 35% from 4 months to 2.8 years (mean, 1.1 years) after surgery and earlier imaging examinations with negative findings. The overall 1-year and 5-year survival probabilities were 71% and 28%, respectively. Patients with MR imaging evidence of disseminated leptomeningeal tumor had a median survival rate of 16 months compared with 149 months for those without disseminated tumor (P < .004, logrank test). CONCLUSION: AT/RTs are typically intra-axial lesions, which can be infra- and/or supratentorial. The unenhanced and enhanced MR imaging features of AT/RT are often variable secondary to cystic/necrotic changes, hemorrhage, and/or calcifications. Poor prognosis is associated with MR imaging evidence of disseminated leptomeningeal tumor.     

Multiple reproducibility indices for evaluation of cognitive functional MR imaging paradigms

BACKGROUND AND PURPOSE: The purpose of this study was to evaluate a variety of reproducibility indices for cognitive functional MR imaging (fMRI) paradigms that account for both overlapping and extraneous regions of activation. METHODS: Eight right-handed volunteers were imaged with fMRI by using a word-generation paradigm and a forward-backward text-listening paradigm. The paradigms were performed twice in the session and repeated 1 week later. Reproducibility indices for the four repeated studies were determined on the basis of pair-wise computation of the ratio of the probability-weighted intersection volume divided by the union volume of surviving activation clusters. The intersection volume was determined by using several iterations of the morphologic dilatation operator with additional voxels accrued in the intersection weighted by an exponential function. Computed indices included global reproducibility, language area reproducibility, extraneous activation reproducibility, and laterality. RESULTS: The word-generation paradigm had reproducibility values that were significantly greater than those of the forward-backward text-listening paradigm (global reproducibility, 0.75 vs 0.5, P <.005; language area reproducibility, 0.85 vs 0.6, P <.008; mean extraneous activation reproducibility, 0.68 vs 0.41, P <.002). The forward-backward text-listening paradigm demonstrated more focal activations, whereas the word-generation demonstrated larger activations outside the dominant language areas that were highly reproducible. CONCLUSION: For clinically relevant language paradigms, multiple reproducibility indices should be taken into account in selecting an appropriate paradigm. Compared with a forward-backward text-listening task, a word-generation task has higher reproducibility indices at the expense of localizing ability. The forward-backward paradigm demonstrates more focal activations with less extraneous activation.     

Cranial Nerve Clock: Part II: Functional MR Imaging of Brain Activation during a Declarative Memory Task

RATIONALE AND OBJECTIVES: The authors performed this study to assess brain activation during encoding and successful recall with a declarative memory paradigm that has previously been demonstrated to be effective for teaching students about the cranial nerves. MATERIALS AND METHODS: Twenty-four students underwent functional magnetic resonance (MR) imaging during encoding and recall of the name, number, and function of the 12 cranial nerves. The students viewed mnemonic graphic and text slides related to individual nerves, as well as their respective control slides. For the recall paradigm, students were prompted with the numbers 1-12 (test condition) intermixed with the number 14 (control condition). Subjects were tested about their knowledge of cranial nerves outside the MR unit before and after functional MR imaging. RESULTS: Students learned about the cranial nerves while undergoing functional MR imaging (mean post- vs preparadigm score, 8.1 +/- 3.4 [of a possible 12] vs 0.75 +/- 0.94, bilateral prefrontal cortex, left greater than right; P < 2.0 x 10(-12)) and maintained this knowledge at I week. The encoding and recall paradigms elicited distributed networks of brain activation. Encoding revealed statistically significant activation in the bilateral prefrontal cortex, left greater than right [corrected]; bilateral occipital and parietal associative cortices, parahippocampus region, fusiform gyri, and cerebellum. Successful recall activated the left much more than the right prefrontal, parietal associative, and anterior cingulate cortices; bilateral precuneus and cerebellum; and right more than the left posterior cingulate. CONCLUSION: A predictable pattern of brain activation at functional MR imaging accompanies the encoding and successful recall of the cranial nerves with this declarative memory paradigm.     

The effect of age on odor-stimulated functional MR imaging.

BACKGROUND AND PURPOSE: The effects of age, sex, and handedness on olfaction have not been adequately addressed with odor-stimulated functional MR imaging studies. We sought to determine the effect of age on functional MR imaging experiments performed with odor stimulation. METHODS: Five right-handed subjects with a mean age of 73 years and five right-handed subjects with a mean age of 24 years underwent gradient-echo echo-planar functional MR imaging using binasal olfactory stimulation. Imaging parameters included 3000/30 (TR/TE) and a 5-mm section thickness in a 6-minute sequence with 30 seconds of pulsed odorants alternating with 30 seconds of room air. The data were normalized to a standard atlas, and individual and group statistical parametric maps (SPMs) were generated for each task. The SPMs were thresholded for a P < .01, and the volumes of activation and distribution of cluster maxima were compared for the two groups. RESULTS: Analysis of the group SPMs revealed activated voxels in the frontal lobes, perisylvian regions, and cingulate gyri, with greater volume in the younger group than in the older group. The right inferior frontal, right perisylvian, and right and left cingulum had the largest number of voxels activated. The most common sites of activation on individual maps in both groups were the right inferior frontal regions and the right and left superior frontal and perisylvian zones. CONCLUSION: Given similar olfactory task paradigms, younger subjects showed a greater number of activated voxels than did older subjects. One must be cognizant of this effect when designing studies of odor-stimulated functional MR imaging.     

Functional 3.0-T MR assessment of higher cognitive function: are there advantages over 1.5-T imaging?

PURPOSE: To compare cortical activation patterns associated with manual motor decision tasks at 1.5- and 3.0-T functional magnetic resonance (MR) imaging. MATERIALS AND METHODS: The local ethics committee approved this study, and informed written consent was obtained. Ten right-handed healthy volunteers (eight men and two women; mean age, 35 years +/- 7 [standard deviation]) underwent functional MR imaging twice, once at 1.5 T and once at 3.0 T, while performing cognitive tasks that demanded manual motor decisions (letter-finger matching and lexical and semantic decisions). While stimulus presentation was blocked, an event-related model was employed to analyze subjects' individual responses. A group analysis of functional data was performed with a t test of 1.5- and 3.0-T results in the 10 subjects. RESULTS: Manual motor decisions activated a widespread network of motor- (primary motor, posterior parietal) and decision-related areas (superior frontal cortex or anterior cingulate) at both field strengths (P <.05, corrected). Moreover, additional functional activation was detected in medial (supplementary motor area) and dorsal premotor regions (P <.05, corrected) at 3.0-T functional MR imaging, which was not detectable with corresponding 1.5-T imaging. The mean t value for peak voxels in activated areas detectable with both systems was 1.3 times larger at 3.0 T than that at 1.5 T. CONCLUSION: Functional 3.0-T MR imaging allows detection of additional activation in cortical areas involved in higher executive motor functions compared with functional 1.5-T MR imaging.     

数字记忆广度与数字工作记忆的功能磁共振比较研究

目的比较数字记忆广度与数字工作记忆的脑区激活特点与差异。方法利用Siemens 1.5T MR机对12名右利手志愿者进行7位数数字记忆广度与2位数数字工作记忆实验,实验采用组块设计,2组任务均设相应对照任务,将记忆任务与对照任务比较,数据采用SPM99软件进行分析和脑功能区定位。结果进行2组任务时,志愿者额叶的Brodmann6区、9区和47区,顶叶的7区和40区,扣带回,海马结构,纹状体以及小脑均有激活。进行数字记忆广度测试时,双侧枕叶Brodmann18区、19区的激活尤其显著,无明显的半球优势,双侧颞叶Brodmann37区也有激活,而进行数字工作记忆时,则在额叶的激活最为显著,额叶和顶叶的激活都表现为左侧半球优势。结论脑区在进行不同要求的短时数字记忆任务时所参与的阶段和所起的作用不同,通过fMRI的研究对推断大脑进行数字信息的处理过程有一定的帮助。     

Subcortical damage and cortical functional changes in men and women with Fabry disease: a multifaceted MR study

PURPOSE: To prospectively compare brain magnetic resonance (MR) imaging and hydrogen 1 (1H) MR spectroscopy findings and to use functional MR imaging to explore the patterns of brain activation in men and women with Fabry disease (FD). MATERIALS AND METHODS: Eight men and eight women with FD (mean age, 38.8 years +/- 13.9 [standard deviation]) with absent or mild neurologic deficit and 16 healthy control subjects (eight men and eight women; mean age, 42.7 years +/- 15.3) gave informed consent to participate in the study, which was approved by the local ethical committee. Patients and control subjects underwent MR imaging, 1H MR spectroscopy of the frontal cortex and subcortical white matter, and functional MR imaging during repetitive flexion-extension of the last four fingers of the right hand. Extent of cerebral white matter damage was rated on fluid-attenuated inversion recovery MR images by using a visual score. Areas of activation were identified by using statistical parametric mapping software and the adoption of a height threshold of P < .001 (uncorrected) and an extent threshold of P < .05 (corrected). RESULTS: Men and women with FD showed a similar distribution of cerebral white matter changes, lacunar and cortical infarcts, small hemorrhages, and vertebrobasilar dolichoectasia. No significant (P > .05) difference was observed between patients with FD and control subjects for concentration of N-acetylaspartate, creatine, and choline. During the motor task, patients showed recruitment of additional cortical areas in comparison with control subjects. Increased activation of the contralateral sensorimotor area correlated (P = .002) with extent of white matter damage. CONCLUSION: Subcortical ischemic changes in men and women with FD are similar and are associated with increased recruitment of the sensorimotor network during a simple motor task, which might limit the functional effect of the white matter small-vessel disease.     

Investigation of higher-order cognitive functions during exposure to a high static magnetic field

Purpose:

To test for potential changes in higher‐order cognitive processes related to the exposure to a high static magnetic field.

Materials and Methods:

Twenty‐four healthy volunteers participated in two experimental sessions inside a 3 Tesla (T) magnetic resonance imaging (MRI) magnet. During one session the magnetic field was ramped down. The tasks consisted of six well‐established paradigms probing a variety of cognitive functions. Reaction times (RT) and accuracies (AC) were recorded for statistical analysis.

Results:

The overall performance was very similar in both sessions. Strong task‐specific effects (all P < 0.006) were consistent with previously published results. Direct comparisons of task‐specific effects between the two sessions (magnetic field on or off) remained insignificance for all paradigms (RT: all P > 0.196; AC: all P > 0.17; no corrections for multiple comparisons).

Conclusion:

The results did not indicate any apparent safety concerns with respect to cognitive performance in a static magnetic field of a typical whole‐body magnet. In addition, comparisons of cognitive effects from testing situations with and without exposure to high static magnetic fields can be considered valid. J. Magn. Reson. Imaging 2012;36:835–840. © 2012 Wiley Periodicals, Inc.     

Functional MR imaging in Alzheimer's disease during memory encoding

BACKGROUND AND PURPOSE: We applied functional MR imaging with a learning task in healthy elderly volunteers and in patients with Alzheimer's disease to study brain activation during memory performance. The purpose was to determine the feasibility of functional MR imaging during a learning task in healthy elderly volunteers and in patients with Alzheimer's disease and to test our hypothesis that brain activation is decreased in the medial temporal lobe (MTL) memory system in patients with Alzheimer's disease compared with control volunteers. METHODS: In 12 patients with mild to moderate forms of Alzheimer's disease and 10 elderly control volunteers, activation of the MTL memory system was studied. We used two learning tasks that required the encoding of new information into memory. After the functional MR imaging experiment, participants were tested for recognition of the encoded objects. RESULTS: In the elderly control volunteers, activation during memory encoding was observed in medial and lateral temporal lobe structures (fusiform, parietal and occipital parts, and hippocampal formation) and in the frontal cortex, as reported previously in studies of young control volunteers. Focusing on the MTL, we observed that activation was significantly decreased in patients with Alzheimer's disease compared with control volunteers in the left hippocampus and parahippocampal gyrus bilaterally during the first encoding task but not during the second (P < .05, uncorrected). CONCLUSION: Functional MR imaging with a learning task seems feasible in elderly volunteers and in patients with Alzheimer's disease. The measured functional signal decrease in MTL areas warrants further exploration of the (early) diagnostic usefulness of functional MR imaging in cases of Alzheimer's disease and other dementias.     

Assessment of nicorandil therapy in ischemic myocardial injury by using contrast-enhanced and functional MR imaging.

PURPOSE: To determine the potential of mesoporphyrin- and gadopentetate dimeglumine-enhanced and functional magnetic resonance (MR) imaging in the assessment of the acute effect of nicorandil on ischemic injury of the myocardium. MATERIALS AND METHODS: Spin-echo MR imaging was used to monitor changes in myocardial contrast and function in reperfused myocardial injury. Inversion-recovery echo-planar MR imaging was used to depict the injured region. Myocardial injury in rats was produced by using 30 minutes of coronary occlusion followed by 24 hours reperfusion. Nicorandil (n = 9) was infused during occlusion and early reperfusion. Control animals (n = 11) received no therapy. At 24 hours, after administration of mesoporphyrin and gadopentetate dimeglumine and histochemical staining, the function and size of the injured region of the left ventricle (LV) were determined. A t test was used to compare data between groups of animals, whereas regression and Bland-Altman analyses were used to determine correlation and agreement between MR imaging and histomorphometry, respectively. RESULTS: Treated animals showed reduced infarction size as compared with the control group from 25.6% +/- 7.9 (SD) to 7.9% +/- 6.8 of LV myocardial area (P < .001), as defined with mesoporphyrin-enhanced MR imaging; while the size of the rim increased from 10.8% +/- 10.0 to 16.1% +/- 14.4 (P < .05). The diastolic-midventricular cavity area was smaller in treated animals (15.2 mm(2) +/- 4.3) compared with the control group (28.5 mm(2) +/- 7.9; P < .001). At functional MR imaging, nicorandil improved systolic reduction in LV cavity area (57.5% +/- 17.3) compared with the control group (38.0% +/- 16.0; P < .05) and preserved regional LV wall thickening at the site of injury (12.2% +/- 11.1 in treated group vs 0.3% +/- 8.6 in the control group; P < .05). CONCLUSION: Contrast material-enhanced MR imaging has the potential to demonstrate reduction in size of ischemically injured myocardium, whereas functional MR imaging demonstrated the recovery of LV function 24 hours after nicorandil therapy.     

Neuroimaging in pediatric brain tumors: Gd-DTPA-enhanced, hemodynamic, and diffusion MR imaging compared with MR spectroscopic imaging

BACKGROUND AND PURPOSE: Gadolinium-enhanced MR images assist in defining tumor borders; however, the relation between tumor cell extent and contrast-enhanced regions is unclear. Our aim was to improve conventional neuroimaging of pediatric brain tumors with hemodynamic, diffusion, and spectroscopic MR imaging. METHODS: We performed conventional MR and MR spectroscopic imaging in 31 children with neuroglial brain tumors. Hemodynamic MR imaging was performed in 16 patients with a first-pass intravenous bolus of gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA); apparent diffusion coefficients (ADCs) were measured in 12 patients. To account for multiple measurements in a patient, we used a nested analysis of variance. RESULTS: At MR spectroscopy, choline (Cho)-containing compounds (indicating tumor) and lipid levels (indicating necrosis) did not correlate with percent Gd-DTPA enhancement on MR images. Percent enhancement was positively correlated with relative cerebral blood volumes (rCBVs) (P =.05) and negatively correlated with ADCs (P <.001). Stepwise multiple linear regression revealed that rCBV (P =.008), ADC (P =.022), and lipid (P <.001) levels were significant independent predictors of percent enhancement. Tumor spectral patterns were detected in tumor regions and outside enhancing tumor beds in patients with clinical progression; these were confirmed at neuropathologic analysis. CONCLUSION: MR spectroscopic imaging improves the assessment of pediatric brain tumors by adding biochemical information regarding tumor involvement and by depicting residual or recurrent tumor outside the Gd-DTPA-enhanced tumor bed. rCBV and ADC mapping complemented MR spectroscopic imaging. We recommend the use of MR spectroscopic imaging in addition to conventional MR imaging in assessing pediatric brain tumors.     

Cardiac functional analysis with multi-detector row CT and segmental reconstruction algorithm: comparison with echocardiography, SPECT, and MR imaging

PURPOSE: To evaluate accuracy of cardiac functional analysis with multi-detector row computed tomography (CT) and segmental reconstruction algorithm over a range of heart rates. MATERIALS AND METHODS: Institutional review board approval was obtained. Informed consent was not required. Multi-detector row CT (500-msec rotation time, 8 x 1-mm detector collimation) and magnetic resonance (MR) imaging were performed in 50 patients (28 men, 22 women; age range, 46-84 years; mean age, 67 years). Two-dimensional echocardiography was performed in 41 patients, and electrocardiographically (ECG)-gated single photon emission computed tomography (SPECT) was performed in 27. End-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF), and left ventricular (LV) mass were estimated with multi-detector row CT and compared with values estimated with MR imaging, which served as the reference standard. Additionally, EF values estimated with multi-detector row CT, echocardiography, and SPECT were compared with those estimated with MR imaging. Systemic error and degree of agreement of global functional parameters measured with MR imaging and other modalities were assessed. In a second analysis, linear regression analysis was added. RESULTS: EF estimated with multi-detector row CT agreed and correlated well with EF estimated with MR imaging (bias +/- standard deviation, -1.2% +/- 4.6; r = 0.96). Agreement and correlation were similar for EDV (-0.35 mL +/- 15.2; r = 0.97), ESV (1.1 mL +/- 8.6; r = 0.99), and LV mass (2.5 mL +/- 15.0; r = 0.96). Standard deviation of EF difference between multi-detector row CT and MR imaging was significantly less than that between echocardiography and MR imaging (P < .001) or that between SPECT and MR imaging (P < .001). CONCLUSION: Various LV functional parameters were measured with multi-detector row CT with a segmental approach, and measurements correlated and agreed with those obtained with MR imaging. Moreover, functional analysis with multi-detector row CT was more accurate than that with two-dimensional echocardiography or ECG-gated SPECT.     

Exogenous gene expression in tumors: noninvasive quantification with functional and anatomic imaging in a mouse model

PURPOSE: To assess whether a combination of functional (planar imaging and single photon emission computed tomography [SPECT]) and anatomic (magnetic resonance [MR] imaging) imaging techniques can be used to noninvasively quantify tumor expression of a somatostatin receptor type 2A (SSTR2A) gene chimera in vivo. MATERIALS AND METHODS: All animal experiments were approved by the institutional animal care and use committee. Expression of the SSTR2A gene chimera was quantified in vitro, in vivo, and ex vivo. The epitope tag of the fusion protein was detected through an antibody, and the receptor portion was detected by using the Food and Drug Administration-approved radiopharmaceutical indium 111 octreotide. Six mice were injected with cells transfected with vector and with two clonal cell lines that each expressed different amounts of the gene chimera. With a dedicated small-animal gamma camera, planar imaging and SPECT were used for quantification of radiopharmaceutical uptake in vivo; 4.7-T MR imaging was used to derive tumor weight. After imaging, excised tumors were evaluated for uptake and weight. For statistical analysis, linear regression analysis, Wilcoxon rank sum test, and Kruskal-Wallis test were employed. RESULTS: Different expression levels of the chimeric gene were confirmed in vitro. Radiopharmaceutical uptake assessed in excised tumors and that derived from in vivo planar (r = 0.94, P < .05, n = 18) or SPECT (r = 0.90, P < .05, n = 18) images correlated. Weight of excised tumors and that derived from MR images (r = 0.98, P < .05, n = 18) correlated. MR images also allowed morphologic assessment. The biodistribution parameter of percentage of injected dose per gram of excised tumors correlated with the same measure derived from a combination of planar (r = 0.90, P < .05, n = 18) or SPECT (r = 0.87, P < .05, n = 18) images and MR images. CONCLUSION: A combination of noninvasive functional and anatomic imaging can be used in vivo to quantify gene transfer in tumors.     

Mild cognitive impairment: evaluation with 4-T functional MR imaging

PURPOSE: To prospectively assess abnormalities in brain activation patterns during encoding and retrieval in subjects with mild cognitive impairment by using 4-T functional magnetic resonance (MR) imaging. MATERIALS AND METHODS: The institutional review board approved this HIPAA-compliant study; all subjects gave written informed consent. Twenty patients with mild cognitive impairment (12 men, eight women; mean age, 75.0 years +/- 7.6 [standard deviation]) and 20 elderly control subjects (nine men, 11 women; mean age, 71.2 years +/- 4.5) underwent functional MR imaging at 4 T during a novel-versus-familiar face-name encoding-retrieval task. The magnitude of blood oxygen level-dependent brain responses across the entire brain were compared within and between subjects with mild cognitive impairment and control subjects by using a voxelwise random-effects model. A one-sample t test was used for within-group analysis; an analysis-of-covariance model (with age as a covariate) was used for between-group analysis. RESULTS: Brain regions activated by the task (prefrontal, medial temporal, and parietal regions) during encoding were similar to those activated during retrieval, with larger areas activated during retrieval. Subjects with mild cognitive impairment showed decreased magnitude of activation in bilateral frontal cortex regions (during encoding and retrieval), the left hippocampus (during retrieval), and the left cerebellum (during encoding) compared with magnitude of activation in control subjects (P < .001). Patients with mild cognitive impairment showed increased activation in the posterior frontal lobes (during retrieval) (P < .001). Lower hippocampal activation during retrieval was the most significant correlate of clinical severity of memory loss in mild cognitive impairment (P < .001). CONCLUSION: A difference exists in the response of brain regions underlying encoding and retrieval in mild cognitive impairment. Memory deficits in mild cognitive impairment may be linked to functional alterations in several specific brain regions both inside and outside the medial temporal lobe.     

What is different about a radiologist's brain?

PURPOSE: To investigate neuronal activations during processing of radiologic and nonradiologic images by experienced radiologists and nonradiologist subjects by using event-related functional magnetic resonance (MR) imaging. MATERIALS AND METHODS: Study was approved by local ethics committee, and informed consent was obtained. Radiologic and control images were presented to 12 experienced radiologists (mean age, 35.8 years +/- 3.6 [standard deviation]) and 12 nonradiologist subjects (mean age, 33.0 years +/- 6.9). Half of the images were artificially manipulated-that is, for example, a local shadow was introduced. Subjects had to indicate whether a visually presented image was original or manipulated, while neuronal activity was assessed by using event-related functional MR imaging. Analysis was performed on the basis of fixed-effects general linear models with correction for multiple comparisons (false discovery rate). RESULTS: Radiologic images, when compared with control images, evoked stronger activations exclusively in the group of radiologists, notably in the bilateral middle and inferior temporal gyrus, bilateral medial and middle frontal gyrus, and left superior and inferior frontal gyrus (P < .001, corrected). Additionally, visual processing of control images (ie, nonradiologic images) differed significantly between experienced radiologists and nonradiologist subjects (P < .001, corrected). Radiologists showed strongest activation in the left-dominant more posterior superior and inferior parietal lobule, while nonradiologist subjects showed strongest activation in the right-dominant more anterior superior and inferior parietal lobule and postcentral gyrus. CONCLUSION: With radiologic experience, there is selective enhancement of brain activation with radiologic images, and the visual system is modified in general.     

PET/MR images acquired with a compact MR-compatible PET detector in a 7-T magnet

PURPOSE: To prospectively use compact avalanche photodiodes instead of photomultiplier tubes to integrate a positron emission tomographic (PET) detector and a 7-T magnetic resonance (MR) imager. MATERIALS AND METHODS: All animal experiments were performed in accordance with the University of Tübingen guidelines and the German law for the protection of animals. A compact lutetium oxyorthosilicate-avalanche photodiode PET detector was built and optimized to operate within a 7-T MR imager. The detector performance was investigated both outside and inside the magnet, and MR image quality was evaluated with and without the PET detector. Two PET detectors were set up opposite each other and operated in coincidence to acquire PET images in the step-and-shoot mode in a mouse head specimen after injection of fluorine 18 fluorodeoxyglucose. RESULTS: The performance of the PET detector when operated inside the magnet during MR image acquisition showed little degradation in energy resolution (increase from 14.6% to 15.9%). The PET detector did not influence MR imaging. The fused PET and MR images showed an anatomic match and no degradation of image quality. CONCLUSION: Simultaneous PET and MR imaging with a 7-T system was deemed feasible.