ISAS (Ictal-Interictal SPECT Analysis by SPM)
Encyclopedia
The goal of ictal Single Photon Emission Computed Tomography (SPECT)
is to localize the region of seizure
onset for epilepsy
surgery planning. ISAS (Ictal-Interictal SPECT Analysis by SPM
) is an objective tool for analyzing ictal vs. interictal SPECT scans. ISAS was introduced and validated in two recent studies (Chang et al., 2002; McNally et al., 2005). This site is a technical supplement to (McNally et al., 2005), which should enable ISAS to be implemented at any center for further study and analysis.
between the interictal and ictal SPECT can then be detected. The analysis is conducted using SPM (statistical parametric mapping).
Cerebral blood flow is known to increase during seizures at the site of seizure onset. Since SPECT is an indicator of CBF, increases in the SPECT during seizures can be useful for seizure localization. CBF decreases are more complicated, and occur both during and following seizures in multiple locations. Details of ISAS interpretation can be found in McNally et al., 2005, but in summary:
1. For true ictal SPECT (patient injected before end of seizure), seizure onset can be reliably localized based on SPECT increases.
2. For post-ictal SPECT, seizure onset cannot be reliably localized to a single lobe based on SPECT increase or decreases. However, the side (L or R) of seizure onset can be reliably determined based on which hemisphere has greater overall SPECT decreases (hypoperfusion asymmetry index).
The requirements for implementing ISAS are relatively simple. All that is needed is a computer running MATLAB
and an operator with sufficient imaging experience to download and implement the SPM (statistical parametric mapping) analysis.
NOTE: ISAS has been tested and confirmed to work with SPM2 and the following MATLAB versions - 6.1, 6.5.1, and 7.0.4. In order to ensure correctness, both Matlab and SPM should be kept updated with the latest service packs and patches. Refer to the software setup section of our site for more information.
Please see the ISAS website (http://spect.yale.edu/) for detailed instructions implementing ISAS.
The intent of ISAS and the ISAS website is to begin to fill the need for epilepsy SPECT image analysis, by providing a freely available method that can be implemented anywhere.
This study, together with the ISAS website, provides a complete description of the ISAS method, and validates this approach with a group of mesial temporal and neocortical epilepsy patients.
2. Chang DJ, Zubal IG, Gottschalk C, Necochea A, Stokking R, Studholme C, Corsi M, Slawski J, Spencer SS, Blumenfeld H (2002). Comparison of Statistical Parametric Mapping and SPECT Difference Imaging in Patients with Temporal Lobe Epilepsy. Epilepsia , 43:68-74.
ISAS was introduced in this study, and compared to conventional SPECT difference imaging.
3. Lee JD, Kim HJ, Lee BI, Kim OJ, Jeon TJ, Kim MJ (2000). Evaluation of ictal brain SPET using statistical parametric mapping in temporal lobe epilepsy. European Journal of Nuclear Medicine 27:1658-1665.
This paper is the first use of ictal SPECT analysis by SPM for seizure localization.
4. O'Brien TJ, So EL, Mullan BP, Hauser MF, Brinkmann BH, Bohnen NI, Hanson D, Cascino GD, Jack CR, Jr., Sharbrough FW (1998). Subtraction ictal SPECT co-registered to MRI improves clinical usefulness of SPECT in localizing the surgical seizure focus. Neurology , 50:445-454.
This paper describes SISCOM (subtraction ictal SPECT coregistered with MRI), a widely used method of ictal-interictal difference imaging (see also below).
5. Zubal IG, Spencer SS, Imam K, Seibyl J, Smith EO, Wisniewski G, Hoffer PB (1995). Difference images calculated from ictal and interictal technetium-99m-HMPAO SPECT scans of epilepsy. Journal of Nuclear Medicine , 36:684-689.
This is the first paper which describes the use of ictal-interictal difference imaging coregistered with MRI for epilepsy surgery localization.
Single photon emission computed tomography
Single-photon emission computed tomography is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera. However, it is able to provide true 3D information...
is to localize the region of seizure
Seizure
An epileptic seizure, occasionally referred to as a fit, is defined as a transient symptom of "abnormal excessive or synchronous neuronal activity in the brain". The outward effect can be as dramatic as a wild thrashing movement or as mild as a brief loss of awareness...
onset for epilepsy
Epilepsy
Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...
surgery planning. ISAS (Ictal-Interictal SPECT Analysis by SPM
Statistical parametric mapping
Statistical parametric mapping or SPM is a statistical technique created by Karl Friston for examining differences in brain activity recorded during functional neuroimaging experiments using neuroimaging technologies such as fMRI or PET...
) is an objective tool for analyzing ictal vs. interictal SPECT scans. ISAS was introduced and validated in two recent studies (Chang et al., 2002; McNally et al., 2005). This site is a technical supplement to (McNally et al., 2005), which should enable ISAS to be implemented at any center for further study and analysis.
Analysis
The basic idea of ISAS is to compute the difference between an ictal and interictal SPECT scan for a single patient. The differences of the ictal/inter-ictal comparison are checked against a healthy normal database to determine the normal expected variation. Significant increases and decreases in CBF (cerebral blood flow)Cerebral blood flow
Cerebral blood flow, or CBF, is the blood supply to the brain in a given time. In an adult, CBF is typically 750 millitres per minute or 15% of the cardiac output. This equates to 50 to 54 millilitres of blood per 100 grams of brain tissue per minute. CBF is tightly regulated to meet the brain's...
between the interictal and ictal SPECT can then be detected. The analysis is conducted using SPM (statistical parametric mapping).
Cerebral blood flow is known to increase during seizures at the site of seizure onset. Since SPECT is an indicator of CBF, increases in the SPECT during seizures can be useful for seizure localization. CBF decreases are more complicated, and occur both during and following seizures in multiple locations. Details of ISAS interpretation can be found in McNally et al., 2005, but in summary:
1. For true ictal SPECT (patient injected before end of seizure), seizure onset can be reliably localized based on SPECT increases.
2. For post-ictal SPECT, seizure onset cannot be reliably localized to a single lobe based on SPECT increase or decreases. However, the side (L or R) of seizure onset can be reliably determined based on which hemisphere has greater overall SPECT decreases (hypoperfusion asymmetry index).
The requirements for implementing ISAS are relatively simple. All that is needed is a computer running MATLAB
MATLAB
MATLAB is a numerical computing environment and fourth-generation programming language. Developed by MathWorks, MATLAB allows matrix manipulations, plotting of functions and data, implementation of algorithms, creation of user interfaces, and interfacing with programs written in other languages,...
and an operator with sufficient imaging experience to download and implement the SPM (statistical parametric mapping) analysis.
NOTE: ISAS has been tested and confirmed to work with SPM2 and the following MATLAB versions - 6.1, 6.5.1, and 7.0.4. In order to ensure correctness, both Matlab and SPM should be kept updated with the latest service packs and patches. Refer to the software setup section of our site for more information.
Please see the ISAS website (http://spect.yale.edu/) for detailed instructions implementing ISAS.
The intent of ISAS and the ISAS website is to begin to fill the need for epilepsy SPECT image analysis, by providing a freely available method that can be implemented anywhere.
Selected References
1. McNally KA, Paige AL, Varghese G, Zhang H, Novotny EJ, Spencer SS, Zubal IG, Blumenfeld H. (2005). Seizure localization by ictal and postictal SPECT. Epilepsia , 46(9):1–15, 2005This study, together with the ISAS website, provides a complete description of the ISAS method, and validates this approach with a group of mesial temporal and neocortical epilepsy patients.
2. Chang DJ, Zubal IG, Gottschalk C, Necochea A, Stokking R, Studholme C, Corsi M, Slawski J, Spencer SS, Blumenfeld H (2002). Comparison of Statistical Parametric Mapping and SPECT Difference Imaging in Patients with Temporal Lobe Epilepsy. Epilepsia , 43:68-74.
ISAS was introduced in this study, and compared to conventional SPECT difference imaging.
3. Lee JD, Kim HJ, Lee BI, Kim OJ, Jeon TJ, Kim MJ (2000). Evaluation of ictal brain SPET using statistical parametric mapping in temporal lobe epilepsy. European Journal of Nuclear Medicine 27:1658-1665.
This paper is the first use of ictal SPECT analysis by SPM for seizure localization.
4. O'Brien TJ, So EL, Mullan BP, Hauser MF, Brinkmann BH, Bohnen NI, Hanson D, Cascino GD, Jack CR, Jr., Sharbrough FW (1998). Subtraction ictal SPECT co-registered to MRI improves clinical usefulness of SPECT in localizing the surgical seizure focus. Neurology , 50:445-454.
This paper describes SISCOM (subtraction ictal SPECT coregistered with MRI), a widely used method of ictal-interictal difference imaging (see also below).
5. Zubal IG, Spencer SS, Imam K, Seibyl J, Smith EO, Wisniewski G, Hoffer PB (1995). Difference images calculated from ictal and interictal technetium-99m-HMPAO SPECT scans of epilepsy. Journal of Nuclear Medicine , 36:684-689.
This is the first paper which describes the use of ictal-interictal difference imaging coregistered with MRI for epilepsy surgery localization.
External links
- ISAS (Ictal-Interictal SPECT Analysis by SPM) - Yale University
- Wikibooks SPM Wikibook.
- SPM software and documentation from the Wellcome Department of Imaging Neuroscience.