SPECT Brain Imaging

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Brain perfusion single-photon emission computed tomography (SPECT) imaging is a functional nuclear imaging technique performed to evaluate regional cerebral perfusion.

Because cerebral blood flow is closely linked to neuronal activity, the activity distribution is presumed to reflect neuronal activity levels in different areas of the brain. A lipophilic, PH-neutral radiopharmaceutical (most commonly^99m Tc-hexamethylpropyleneamine oxime [HMPAO] and^99m Tc-ethylene cysteine diethylester [ECD], with a half-life of 6.02 hours) is injected into the patient, which crosses the blood-brain barrier and continues to emit gamma rays. ^{[1, 2]} A 3-dimensional representation of cerebral blood flow can be iterated using gamma detectors, allowing for interpretation.

Brain SPECT can be complemented with pharmaceutical agents that enhance regional cerebral blood flow, such as acetazolamide (carbonic anhydrase). Acetazolamide increases local pCO₂ and causes arteriolar dilation, allowing for assessment of cerebrovascular reserve in transient ischemic attack, stroke, and vascular anomalies and distinguishing vascular from neuronal causes of dementia. ^[3]

Brain SPECT imaging has many different clinical applications.

Brain perfusion SPECT imaging can aid in the diagnosis and ongoing evaluation of many different medical conditions, as follows:

Detection and evaluation of cerebrovascular disease

Aid in the diagnosis and differential diagnoses of suspected dementia

Detection of seizure focus

Assessment of brain death

Evaluating suspected brain trauma

Neuropsychiatric disorders: Mood disorders, evaluating and subtyping attention-deficit disorder

Substance abuse

Infection/inflammation

Brain SPECT imaging is contraindicated in the following:

Pregnancy

Breastfeeding (this should be interrupted for 24 hours prior to imaging)

Lack of cooperation

Brain SPECT imaging is a safe procedure on the whole. However, care must be provided by the imaging technologist to reduce patient discomfort and minimize motion artifact. Care must also be provided to avoid tissue extravasation of radiopharmaceutical agents, as there is potential to induce tissue necrosis.

Juni JE, Waxman AD, Devous MD Sr, Tikofsky RS, Ichise M, Van Heertum RL, et al. Procedure guideline for brain perfusion SPECT using (99m)Tc radiopharmaceuticals 3.0. J Nucl Med Technol. 2009 Sep. 37(3):191-5. [Medline].

Kapucu OL, Nobili F, Varrone A, Booij J, Vander Borght T, Någren K, et al. EANM procedure guideline for brain perfusion SPECT using 99mTc-labelled radiopharmaceuticals, version 2. Eur J Nucl Med Mol Imaging. 2009 Dec. 36(12):2093-102. [Medline].

Farid K, Petras S, Ducasse V, Chokron S, Helft G, Blacher J, et al. Brain perfusion SPECT imaging and acetazolamide challenge in vascular cognitive impairment. Nucl Med Commun. 2012 Jun. 33(6):571-80. [Medline].

Kranert T, Menzel C, Bartenstein P, Brust P, Coenen HH, Krause BJ, et al. [Perfusion brain imaging with SPECT-technique. German Guideline S1]. Nuklearmedizin. 2013. 52(5):157-62; quiz N55. [Medline].

Thrall J, Ziessman H. Central Nervous System. Nuclear Medicine – The Requisites. 1st Ed. United States of America: Mosby; 1995. Nuclear Medicine: 11.

Murray I.P.C, Ell P.J. Lipophilic tracers for the study of regional cerebral blood flow. Van der Wall.H, William Strauss.H. Nuclear Medicine in Clinical Diagnosis and Treatment. 2nd Ed. Edinburgh: Churchill Livingstone; 1998. 1: 42.

Tc99m-HMPAO (Ceretec®)

Tc99m-ECD (Neurolite®)

Transport mechanism

Neutral lipophilic compound

Neutral lipophilic compound

First First-pass cerebral extraction

80%

60%-70%

Peak activity

1-2 minutes postinjection

4%-7% of the dose remains within the brain

1-2 minutes postinjection

6%-7% of the dose remains within the brain

Advantage

Less radiation dose

Rapid brain uptake with excellent brain retention

Higher brain-to-background ratio

Higher gray-to-white matter ratio

Disadvantage

Poor stability

Dose needs to be used within 30 minutes postreconstitution

Higher radiation dose

Currently not available in Australia

Trapping mechanism

Trapped in all living cells; glutathione-mediate conversion to hydrophilic complex

Trapped only in metabolically intact cells and not retained during transient dysfunction; enzymatic (esterases) conversion to hydrophilic products

Radiopharmaceutical

Administered Activity, MBq (mCi)

Organ Receiving the Largest Radiation Dose, mGy (rad)

Effective Dose, mSv (rem)

Tc-99m HMPAO

555-1110 IV

(15-30)

0.034

Kidneys

(0.126)

0.0093

(0.034)

Tc-99m ECD

555-1110 IV

(15-30)

0.073

Bladder wall

(0.27)

0.011

(0.041)

Radiopharmaceutical

Administered Activity,

MBq/kg

(mCi/kg)

Organ Receiving the Largest Radiation Dose, mGy (rad)

Effective Dose, mSv (rem)

Tc-99m HMPAO

7.4–11.1 IV

(0.2-0.3)

0.14

Thyroid

(0.52)

0.026

(0.096)

Tc-99m ECD

7.4-11.1 IV

(0.2-0.3)

0.083

Bladder wall

(0.31)

0.023

(0.085)

Matthew Tam, MBBCh Resident Physician, Nuclear Medicine, Royal Perth Hospital, Australia

Disclosure: Nothing to disclose.

Sylvia Suk Kwan Leung, MPH Nuclear Medicine Technologist, Certified Densitometry Technologist, Department of Nuclear Medicine, Royal Perth Hospital, Australia

Disclosure: Nothing to disclose.

Michael McCarthy, MBBS, FRACP, ANZAPNM Head of Department, Nuclear Medicine Specialist, Department of Nuclear Medicine, Royal Perth Hospital; Nuclear Medicine Imaging Specialist, Perth Radiology Clinics, Australia

Disclosure: Nothing to disclose.

Gowthaman Gunabushanam, MD, FRCR Assistant Professor, Department of Diagnostic Radiology, Yale University School of Medicine

Gowthaman Gunabushanam, MD, FRCR is a member of the following medical societies: American Roentgen Ray Society, Connecticut State Medical Society

Disclosure: Nothing to disclose.

SPECT Brain Imaging

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