Atypical finding of brain Tc-99m-ECD SPECT imaging in herpes simplex encephalitis

Fast direct estimation of the blood input function and myocardial time activity curve from dynamic SPECT projections via reduction in spatial and temporal dimensions

PURPOSE

Reconstruction of parametric images from dynamic single photon emission computed tomography (SPECT) data acquired with slow rotating cameras is a challenge because the estimation of the time-activity curves (TACs) may involve fitting data to an inconsistent underdetermined system of equations. This work presents a novel algorithm for the estimation of the blood input function and myocardial TAC with high accuracy and high efficiency directly from these projections.

METHODS

In the proposed dynamic reconstruction method, the information from the segmentation of functional regions from the static reconstructed image was used as a prior to construct a sparse matrix, through which the spatial distribution of the radioactive tracer was represented. Then the temporal distribution of the radioactive tracer was modeled by nonuniform B-spline basis functions which were determined according to a new selection rule. With reduction in both the spatial and temporal dimensions of the reconstructed image, the blood input function and myocardial TAC were estimated using the 4D maximum likelihood expectation maximization algorithm. The method was validated using data from both digital phantom simulations and an experimental rat study.

RESULTS

Compared with the conventional dynamic SPECT reconstruction method without the reduction in spatial dimensions, the proposed method provides more accurate TACs with less computation time in both phantom simulation studies and a rat experimental study.

CONCLUSIONS

The proposed method is promising in both providing more accurate time-activity curves and reducing the computation time, which makes it practical for small animal studies using clinical systems with slow rotating cameras.

Dynamic single photon emission computed tomography--basic principles and cardiac applications

The very nature of nuclear medicine, the visual representation of injected radiopharmaceuticals, implies imaging of dynamic processes such as the uptake and wash-out of radiotracers from body organs. For years, nuclear medicine has been touted as the modality of choice for evaluating function in health and disease. This evaluation is greatly enhanced using single photon emission computed tomography (SPECT), which permits three-dimensional (3D) visualization of tracer distributions in the body. However, to fully realize the potential of the technique requires the imaging of in vivo dynamic processes of flow and metabolism. Tissue motion and deformation must also be addressed. Absolute quantification of these dynamic processes in the body has the potential to improve diagnosis. This paper presents a review of advancements toward the realization of the potential of dynamic SPECT imaging and a brief history of the development of the instrumentation. A major portion of the paper is devoted to the review of special data processing methods that have been developed for extracting kinetics from dynamic cardiac SPECT data acquired using rotating detector heads that move as radiopharmaceuticals exchange between biological compartments. Recent developments in multi-resolution spatiotemporal methods enable one to estimate kinetic parameters of compartment models of dynamic processes using data acquired from a single camera head with slow gantry rotation. The estimation of kinetic parameters directly from projection measurements improves bias and variance over the conventional method of first reconstructing 3D dynamic images, generating time-activity curves from selected regions of interest and then estimating the kinetic parameters from the generated time-activity curves. Although the potential applications of SPECT for imaging dynamic processes have not been fully realized in the clinic, it is hoped that this review illuminates the potential of SPECT for dynamic imaging, especially in light of new developments that enable measurement of dynamic processes directly from projection measurements.

Early dynamic SPECT imaging in acute viral encephalitis

BACKGROUND AND PURPOSE

Several cases have reported that dynamic single-photon emission computed tomography (SPECT) shows increased tracer uptake in acute herpes simplex viral encephalitis (HSVE). The purpose of this study was to evaluate the clinical usefulness of dynamic Tc-ECD SPECT in patients with acute viral encephalitis.

METHOD

We performed the dynamic SPECT in 9 patients with acute viral encephalitis (4 women, 5 men, 49.5 +/- 17.4 years of age at onset). SPECT and magnetic resonance imaging (MRI) were performed within 2 weeks after acute clinical onset and at the time of resolution of acute symptoms.

RESULTS

Cranial MRI showed high intensities in all patients (7 medial temporal and 2 lateral temporal lobes, 1 inferior temporal lobe, 2 insula and adjacent regions, 1 thalamus, 1 putamen). The initial dynamic SPECT showed increased accumulation of tracer, corresponding to the lesions on MRI in 3 patients with HSVE. Resolution of acute symptoms was associated with a reduction in increased tracer uptake. Six patients with non-HSVE showed no increased accumulation of tracer.

CONCLUSIONS

Dynamic SPECT may be a new optional neuroradiologic technique that may help to establish a diagnosis in patients with suspected HSVE.

Technetium-99m Ethyl Cysteinate Dimer Dynamic and Static Single Photon Emission Computed Tomography in Crossed Cerebellar Diaschisis

A 69-year-old man with a past history of right middle cerebral artery (MCA) occlusion had cerebral single photon emission computed tomography (SPECT) with technetium-99m ethyl cysteinate dimer (Tc-99m ECD). Dynamic SPECT in the super-early phase revealed normal uptake in the left cerebellum and hypoactivity in the right MCA territory. Conventional static SPECT revealed decreased cerebral blood flow in the right MCA territory and the left cerebellum, indicating crossed cerebellar diaschisis. Our SPECT studies revealed decreased retention of Tc-99m ECD in the cerebellum manifested as crossed cerebellar diaschisis.

[99mTc-HMPAO brain SPECT in a case of HSV encephalitis]

We present a case of encephalitis caused by Herpes Simplex Virus in a 57 year old woman. The acute picture was suggestive of viral infection without associated neurological symptoms. Due to the posterior appearance of neurological focality, cerebral spinal fluid (CSF) was analyzed. It showed pleocytosis and lymphocytosis, inflammatory process data, and serological test with positivity for Simple Herpes Virus (SHV) subtypes I and II. During admission, other complementary tests were performed: EEG, CT, MRI, cerebral perfusion SPECT; the later supplied significant data regarding anatomical neuroimaging (CT, MRI) in regards to bihemispheral extension of the encephalic condition. Furthermore, after clinical discharge, persistent metabolic abnormality was demonstrated in temporal cortex, responsible for concomitant mixed aphasia.