External reference markers for the correction of head rotation in brain single-photon emission tomography

Accurate reorientation of brain single-photon emission tomography (SPET) is required for quantitative procedures and for correlation with other imaging modalities. Traditionally, brain SPET has utilized reoriented slices parallel to the orbitomeatal line (OML). Reorientation using internal landmarks would be more convenient but has not been systematically compared with the use of external landmarks. We compared the interobserver reproducibility for defining the sagittal and coronal angular deviations using internal landmarks, a visual method based upon external reference markers, and an automated method based upon external reference markers. Internal landmarks were inaccurate for defining the OML whether this was based upon the frontal-occipital or frontal-cerebellar plane. External reference markers resulted in significantly lower interobserver differences for both sagittal and coronal reorientation. An operator-independent implementation proved to be feasible and provided an objective measure of marker coplanarity. In summary, external reference markers should be used when reproducible reorientation and ROI placement are required.     

Attenuation correction single-photon emission computed tomography myocardial perfusion imaging

Clinicians now rely heavily on the results of single-photon emission computed tomography (SPECT) myocardial perfusion imaging for diagnosing coronary disease and for planning therapy. However, the technique is imperfect for these purposes, mainly because of technical limitations, the most prominent of which is the effect of soft-tissue attenuation on apparent tracer distribution. Providers have attempted to compensate for this by a number of indirect approaches. Recently, validated hardware and software solutions for directly correcting image data for soft-tissue attenuation have become widely available commercially. Optimal application requires an understanding of the technical details that differ somewhat from system to system, the quality control prerequisites, knowledge of the importance of the transmission map quality, and how dedicated SPECT and SPECT-computed tomography systems present different challenges. In addition, the clinical literature is expanding rapidly, including studies on diagnostic accuracy, image appearances, quantitative analysis, appropriate patients for attenuation correction, clinical utility, incremental value in relation to ECG-gating, and risk stratification.     

Radiopharmaceuticals for single-photon emission computed tomography brain imaging

In the past 10 years, significant progress on the development of new brain-imaging agents for single-photon emission computed tomography has been made. Most of the new radiopharmaceuticals are designed to bind specific neurotransmitter receptor or transporter sites in the central nervous system. Most of the site-specific brain radiopharmaceuticals are labeled with (123)I. Results from imaging of benzodiazepine (gamma-aminobutyric acid) receptors by [(123)I]iomazenil are useful in identifying epileptic seizure foci and changes of this receptor in psychiatric disorders. Imaging of dopamine D2/D3 receptors ([(123)I]iodobenzamide and [(123)I]epidepride) and transporters [(123)I]CIT (2-beta-carboxymethoxy-3-beta(4-iodophenyl)tropane) and [(123)I]FP-beta-CIT (N-propyl-2-beta-carboxymethoxy-3-beta(4-iodophenyl)-nortropane has proven to be a simple but powerful tool for differential diagnosis of Parkinson's and other neurodegenerative diseases. A (99m)Tc-labeled agent, [(99m)Tc]TRODAT (technetium, 2-[[2-[[[3-(4-chlorophenyl)-8-methyl-8-azabicyclo [3,2,1]oct-2-yl]methyl](2-mercaptoethyl)amino]ethyl]amino] ethanethiolato(3-)]oxo-[1R-(exo-exo)]-), for imaging dopamine transporters in the brain has been successfully applied in the diagnosis of Parkinson's disease. Despite the fact that (123)I radiopharmaceuticals have been widely used in Japan and in Europe, clinical application of (123)I-labeled brain radiopharmaceuticals in the United States is limited because of the difficulties in supplying such agents. Development of (99m)Tc agents will likely extend the application of site-specific brain radiopharmaceuticals for routine applications in aiding the diagnosis and monitoring treatments of various neurologic and psychiatric disorders.     

Accuracy of brain perfusion single-photon emission computed tomography for detecting misery perfusion in adult patients with symptomatic ischemic moyamoya disease

Objective

The purpose of the present study was to determine how accurately relative cerebral blood flow (RCBF) and relative cerebrovascular reactivity (RCVR) to acetazolamide assessed using brain perfusion single-photon emission computed tomography (SPECT) detected misery perfusion identified on positron emission tomography (PET) in adult patients with ischemic moyamoya disease (MMD).

Methods

Oxygen extraction fraction (OEF), RCBF, and RCVR were assessed using ¹⁵O gas PET and N-isopropyl-p-[¹²³I]-iodoamphetamine SPECT without and with acetazolamide challenge, respectively, in 45 patients. Regions of interest (ROIs) were automatically placed in the five middle cerebral artery (MCA) territories in the symptomatic cerebral hemisphere and in the ipsilateral cerebellar hemisphere using a three-dimensional stereotaxic ROI template. For RCBF and RCVR to acetazolamide, the ratio of the MCA ROI to cerebellar ROI was calculated. Of the five MCA ROIs in the symptomatic cerebral hemisphere in each patient, the ROI with the highest and lowest OEF value (two ROIs per patient) was selected for analyses.

Results

A significant square or linear correlation was observed between the OEF and RCBF (correlation coefficient, 0.780) or RCVR (correlation coefficient, ??0.345), respectively. The area under the receiver operating characteristic curve for detecting misery perfusion (OEF?>?51.3%) was significantly greater for the RCBF than for the RCVR (difference between areas, 0.221; p?<?0.0001). Sensitivity, specificity, and positive- and negative-predictive values for the RCBF for detecting misery perfusion were 100, 91, 67, and 100%, respectively. The specificity and positive-predictive value did not differ between the combination of the RCBF and RCVR and the CBF ratio alone.

Conclusions

RCBF assessed using brain perfusion SPECT detects misery perfusion with high sensitivity, a high negative-predictive value, and a low positive-predictive value in adult patients with ischemic MMD. The accuracy of RCVR to acetazolamide assessed using brain perfusion SPECT is lower than that of RCBF.

     

Positron emission tomography and single-photon emission computed tomography brain imaging in the evaluation of dementia

The role of PET and SPECT brain imaging in the initial assessment and differential diagnosis of dementia is beginning to evolve rapidly. Numerous studies confirm the value of functional brain imaging, particularly with FDG-PET imaging, as a potentially cost-effective means of establishing an earlier diagnosis of Alzheimer's disease. Such an approach should allow for a more objective means of establishing which patients will benefit from treatment with cholinesterase inhibitors. In the future, neuroreceptor and plaque burden imaging studies should further enhance the sensitivity and specificity of dementia detection and patient management.     

Normal patterns and variants in single-photon emission computed tomography and positron emission tomography brain imaging

One of the most important issues in evaluating functional brain scans for research or clinical purposes is to be able to identify normal variants. Determining the baseline "normal" state of the brain is not easy to characterize since many normal brain functions and mental processes affect brain activity. This article reviews issues pertaining to the technical and neurophysiological aspects of functional brain imaging that might alter "normal" activity and will also consider how normal brain activity changes throughout the lifespan.     

MR imaging, single-photon emission CT, and neurocognitive performance after mild traumatic brain injury

BACKGROUND AND PURPOSE: Mild traumatic brain injury (mTBI) (Glasgow Coma Scale = 14-15) is a common neurologic disorder and a common cause of neurocognitive deficits in the young population. Most patients recover fully from mTBI, but 15% to 29% of patients have persistent neurocognitive problems. Although a partially organic origin is considered likely, little brain imaging evidence exists for this assumption. The aims of the present study were to establish the prevalence of posttraumatic lesions in mTBI patients on MR images and to assess the relation between these imaging findings and posttraumatic symptoms. Secondly, we explored the value of early posttraumatic single-photon emission CT (SPECT) for the evaluation of mTBI. METHODS: Twenty-one consecutive patients were included in the study. Patients underwent MR examination, technetium-99m hexamethylpropylene amine oxime SPECT, and neurocognitive assessment within 5 days after injury. Neurocognitive follow-up was conducted 2 and 6 months after injury, and MR imaging was repeated after 6 months. Lesion size and brain atrophy were measured on the MR studies. RESULTS: Twelve (57%) of 21 patients had abnormal MR findings, and 11 (61%) of 18 had abnormal SPECT findings. Patients with abnormal MR or SPECT findings had brain atrophy at follow-up. The mean neurocognitive performance of all subjects was within normal range. There was no difference in neurocognitive performance between patients with normal and abnormal MR findings. Patients with abnormal MR findings only showed significantly slower reaction times during a reaction-time task. Seven patients had persistent neurocognitive complaints and one patient met the criteria for a postconcussional syndrome. CONCLUSION: Brain lesions are common after mTBI; up to 77% of patients may have abnormal findings either on MR images or SPECT scans, and these lesions may lead to brain atrophy. The association between hypoperfusion seen on acute SPECT and brain atrophy after 6 months suggests the possibility of (secondary) ischemic brain damage. There is only a weak correlation between neuroimaging findings and neurocognitive outcome.     

轻度脑外伤患者SPECT局部脑血流显像

目的 探讨SPECT脑血流灌注显像在研究轻度脑外伤后临床症状发病机理中的作用。方法对39例无意识丧失、CT检查正常的轻度脑外伤患者进行^99Tc^m-双半胱乙酯(ECD)脑血流灌注断层显像。以双侧小脑平均每像素的均数为参比值，计算各大脑感兴趣区(ROI)放射性计数比值(RAR)。大脑皮质或基底神经节RAR低于70％，颞叶中部低于50％视为异常。结果39例患者中23例(59％)SPECT显示异常，其中3例为弥漫性血流灌注减低，20例为局部血流灌注减低灶，共计74个病灶。伤后3个月内脑血流灌注异常15例，2例为弥漫性血流灌注减低，13例为局灶性血流灌注减低；13例中发现病灶58个。8例受伤3个月后显像异常者，1例为弥漫性血流灌注减低，7例为局灶性血流灌注减低，发现病灶16个。结论 轻度脑外伤后患者主要症状为头痛、头昏、记忆力减退；无意识丧失的脑外伤患者可出现局部脑血流灌注减低，且SPECT检查比CT灵敏。     

Quality of brain perfusion single-photon emission tomography images: multicentre evaluation using an anatomically accurate three-dimensional phantom

The aim of the study was to evaluate the quality of routine brain perfusion single-photon emission tomography (SPET) images in Finnish nuclear medicine laboratories. Twelve laboratories participated in the study. A three-dimensional high resolution brain phantom (Data Spectrum’s 3D Hoffman Brain Phantom) was filled with a well-mixed solution of technetium-99m (110 MBq), water and detergent. Acquisition, reconstruction and printing were performed according to the clinical routine in each centre. Three nuclear medicine specialists blindly evaluated all image sets. The results were ranked from 1 to 5 (poor quality–high quality). Also a SPET performance phantom (Nuclear Associates’ PET/SPECT Performance Phantom PS 101) was filled with the same radioactivity concentration as the brain phantom. The parameters for the acquisition, the reconstruction and the printing were exactly the same as with the brain phantom. The number of detected ”hot” (from 0 to 8) and ”cold” lesions (from 0 to 7) was visually evaluated from hard copies. Resolution and contrast were quantified from digital images. Average score for brain phantom images was 2.7±0.8 (range 1.5–4.5). The average diameter of the ”hot” cylinders detected was 16 mm (range 9.2–20.0 mm) and that of the ”cold” cylinders detected, 11 mm (5.9–14.3 mm) according to visual evaluation. Quantification of digital images showed that the hard copy was one reason for low-quality images. The quality of the hard copies was good only in four laboratories and was amazingly low in the others when comparing it with the actual structure of the brain phantom. The described quantification method is suitable for optimizing resolution and contrast detectability of hard copies. This study revealed the urgent need for external quality assurance of clinical brain perfusion SPET images. Received 2 February and in revised form 31 May 1998     

Reducing the small-heart effect in pediatric gated myocardial perfusion single-photon emission computed tomography

Background

We compared two reconstruction algorisms and two cardiac functional evaluation software programs in terms of their accuracy for estimating ejection fraction (EF) of small hearts (SH).

Methods

The study group consisted of 66 pediatric patients. Data were reconstructed using a filtered back projection (FBP) method without the resolution correction (RC) and an iterative method based on an ordered subset expectation maximization (OSEM) algorithm with the RC. EF was evaluated using two software programs of quantitative gated single-photon emission computed tomography (SPECT) (QGS) and cardioREPO. We compared the EF of gated myocardial perfusion SPECT to echocardiographic measurement (Echo).

Results

Forty-eight of 66 patients had an end-systolic volume < 20 mL which was used as the criterion for being included in the SH group, and the SH effect led to an overestimation of EF. While significant differences were observed between Echo (66.9 ± 5.0%) and QGS-FBP without RC (76.9 ± 8.4%, P < .0001), QGS-OSEM with RC (76.6 ± 8.6%, P < .0001), and cardioREPO-FBP without RC (72.1 ± 10.0%, P = .0011), no significant difference was observed between Echo and cardioREPO-OSEM with RC (67.4 ± 6.1%) in SH group.

Conclusions

In pediatric gated myocardial perfusion SPECT, the SH effect can be significantly reduced when an OSEM algorithm is used with RC in combination with the specific cardioREPO algorithm.

     

Prognostic value of brain perfusion single-photon emission computed tomography (SPECT) for language recovery in patients with aphasia

AIM: To determine the prognostic value of brain perfusion single-photon emission computed tomography (SPECT) in patients with aphasia after a stroke. METHODS: Brain perfusion SPECT with 99mTc-ethyl cysteinate dimer (99mTc-ECD) was used in 16 right-handed patients with aphasia after a left-sided cerebrovascular accident (CVA) in the early chronic period after the onset of CVA. The region of interest (ROI) method was used to calculate the relative regional cerebral blood flow (rCBF) in each cerebral lobe, the thalamus, the putamen and the cerebellum as ratios to the count in the left cerebellar hemisphere. The Standard Language Test of Aphasia (SLTA) was performed twice, once at the same time as SPECT, a mean of 2.3 months after CVA onset (early SLTA), and again a mean of 17.0 months after CVA onset (late SLTA). In addition to the overall language function score, scores for taking dictation (Dictation), oral reading (Speaking) and comprehension (Comprehension) were calculated, and the correlations with each of the rCBF values were evaluated. RESULTS: Left temporal CBF correlated with the late Dictation score; bilateral frontal, bilateral temporal and right parietal CBF correlated with the late Speaking score; and right frontal, left temporal and left occipital CBF correlated with the late Comprehension score. CONCLUSION: Brain perfusion SPECT in the early chronic stage was shown to be useful for predicting recovery from aphasia, recovery of oral reading, ability to take dictation and comprehension.     

Technetium Tc-99m ethyl cysteinate dimer brain single-photon emission CT in mild traumatic brain injury: a prospective study

PURPOSE: To explore the role of single-photon emission CT (SPECT) in initial diagnostic evaluation of patients with mild traumatic brain injury (MTBI) and to identify subgroups in which it may serve as a useful diagnostic tool. MATERIALS AND METHODS: Patients with MTBI seen during a 14-month period were prospectively included in this study. All patients had a CT of head within 12 hours of injury and SPECT by using technetium Tc99m ethyl cysteinate dimer (Tc99m-ECD) within 72 hours of injury. Both SPECT and CT findings were compared with clinical features such as posttraumatic amnesia (PTA), postconcussion syndrome (PCS), and loss of consciousness (LOC). RESULTS: Ninety-two patients with MTBI underwent SPECT in the study period. There were 28 children and 64 adults, with male-to-female ratio of 4.5 to 1. CT findings were abnormal in 31 (34%) and SPECT in 58 (63%). The most common abnormality was hypoperfusion in the frontal lobe(s) in adults and the temporal lobe in children. A significantly higher number of perfusion abnormalities were seen in patients with PTA (P = .03), LOC (P = .02), and PCS (P = .01) than in patients without these symptoms. Compared to CT, SPECT had a much higher sensitivity for detecting an organic basis in these subgroup, of patients (P < .05). CONCLUSION: Tc99m-ECD SPECT can be used as a complementary technique to CT in initial evaluation of patients with MTBI. It is particularly useful in patients having PCS, LOC, or PTA with normal CT scan.     

SPET brain perfusion imaging in mild traumatic brain injury without loss of consciousness and normal computed tomography.

We present SPET brain perfusion findings in 32 patients who suffered mild traumatic brain injury without loss of consciousness and normal computed tomography. None of the patients had previous traumatic brain injury, CVA, HIV, psychiatric disorders or a history of alcohol or drug abuse. Their ages ranged from 11 to 61 years (mean = 42). The study was performed in 20 patients (62%) within 3 months of the date of injury and in 12 (38%) patients more than 3 months post-injury. Nineteen patients (60%) were involved in a motor vehicle accident, 10 patients (31%) sustained a fall and three patients (9%) received a blow to the head. The most common complaints were headaches in 26 patients (81%), memory deficits in 15 (47%), dizziness in 13 (41%) and sleep disorders in eight (25%). The studies were acquired approximately 2 h after an intravenous injection of 740 MBq (20.0 mCi) of 99Tcm-HMPAO. All images were acquired on a triple-headed gamma camera. The data were displayed on a 10-grade colour scale, with 2-pixel thickness (7.4 mm), and were reviewed blind to the patient's history of symptoms. The cerebellum was used as the reference site (100% maximum value). Any decrease in cerebral perfusion in the cortex or basal ganglia less than 70%, or less than 50% in the medial temporal lobe, compared to the cerebellar reference was considered abnormal. The results show that 13 (41%) had normal studies and 19 (59%) were abnormal (13 studies performed within 3 months of the date of injury and six studies performed more than 3 months post-injury). Analysis of the abnormal studies revealed that 17 showed 48 focal lesions and two showed diffuse supratentorial hypoperfusion (one from each of the early and delayed imaging groups). The 12 abnormal studies performed early had 37 focal lesions and averaged 3.1 lesions per patient, whereas there was a reduction to--an average of 2.2 lesions per patient in the five studies (total 11 lesions) performed more than 3 months post-injury. In the 17 abnormal studies with focal lesions, the following regions were involved in descending frequency: frontal lobes 58%, basal ganglia and thalami 47%, temporal lobes 26% and parietal lobes 16%. We conclude that: (1) SPET brain perfusion imaging is valuable and sensitive for the evaluation of cerebral perfusion changes following mild traumatic brain injury; (2) these changes can occur without loss of consciousness; (3) SPET brain perfusion imaging is more sensitive than computed tomography in detecting brain lesions; and (4) the changes may explain a neurological component of the patient's symptoms in the absence of morphological abnormalities using other imaging modalities.     

Attenuation correction in cardiac positron emission tomography and single-photon emission computed tomography

Quantitation in cardiac positron emission tomography (PET) and single-photon emission computed tomography (SPECT) depends on being able to correct for several physical factors that tend to distort the data. One of the most important of these corrections is the correction for attenuation. For PET, cardiac attenuation correction is a reality, although certain problems remain to be solved. For SPECT, recent developments in gamma camera hardware and reconstruction methods have finally made it possible to attempt attenuation correction in a clinical setting. This article reviews the methods available to perform attenuation correction in both PET and SPECT, with emphasis on the commonality between the problems encountered and solutions proposed for each modality.     

Positron emission tomography and single-photon emission computed tomography in substance abuse research

Many advances in the conceptualization of addiction as a disease of the brain have come from the application of imaging technologies directly in the human drug abuser. New knowledge has been driven by advances in radiotracer design and chemistry and positron emission tomography (PET) and single-photon emission computed tomography (SPECT) instrumentation and the integration of these scientific tools with the tools of biochemistry, pharmacology, and medicine. This topic cuts across the medical specialties of neurology, psychiatry, oncology, and cardiology because of the high medical, social, and economic toll that drugs of abuse, including the legal drugs, cigarettes and alcohol, take on society. This article highlights recent advances in the use of PET and SPECT imaging to measure the pharmacokinetic and pharmacodynamic effects of drugs of abuse on the human brain.