Neuroimaging with photon-counting computed tomography: A review of clinical applications

Table 1 Comparison of energy integrating vs photon counting detector systems used in computed tomography

	Energy integrating detectors	Photon counting detectors
Principle of operation	Measures the total energy deposited by all incoming photons, without distinguishing their individual energies	Detects and counts individual photons, measuring their energy levels to differentiate photon spectra
Energy conversion	X-rays, light energy, and electrical energy	X-rays, electrical energy
Detector material	Typically uses scintillators (e.g., cesium iodide) coupled with photodiodes	Utilizes semiconductors (e.g., cadmium telluride or silicon)
Energy resolution	Poor - cannot differentiate photon energies, resulting in a loss of spectral information	High - excellent energy resolution, enabling spectral imaging and material decomposition
Dose efficiency	Lower - loses information due to electronic noise and scatter	Higher - better noise performance and higher signal-to-noise ratio, enabling lower radiation dose
Spatial resolution	Moderate - limited by the size of the scintillator and optical coupling	High - smaller pixel sizes and direct detection improve spatial resolution
Spectral imaging capability	Limited - no ability to differentiate or quantify materials based on photon energy	Superior - enables spectral imaging by separating photons into energy bins for material characterization
Contrast Resolution	Limited - relies on iodine contrast enhancement but lacks the ability to differentiate materials based on energy spectra	High - can improve contrast resolution by distinguishing between materials using energy-specific information
Detector efficiency	Lower - efficiency decreases at higher photon energies due to scattering and light loss in the scintillator	Higher - direct photon-to-electron conversion results in greater efficiency across a wide energy range
Scatter sensitivity	Higher - more susceptible to scatter artifacts, reducing image quality	Lower - better scatter rejection due to energy discrimination
Temporal resolution	Limited - relies on integration over a specific time interval, which may result in temporal blurring	High - fast photon counting allows better temporal resolution for dynamic imaging
Artifacts	Susceptible to beam hardening and metal artifacts due to a lack of spectral differentiation	Reduces beam hardening and metal artifacts by using spectral information
Cost	Lower - widely used and cheaper due to mature technology and simpler design	Higher - emerging technology with more complex manufacturing processes and semiconductor materials
Power consumption	Lower - simpler electronics and integration processes result in reduced power needs	Higher - photon counting electronics and energy discrimination require more power
Longevity and robustness	High - well-established and reliable for routine use	Moderate - sensitive semiconductor materials may be prone to degradation over time or under high doses

Table 2 Summary of established clinical neuroimaging applications of photon-counting computed tomography, along with the key properties of photon-counting computed tomography that provide benefits over conventional computed tomography

Clinical application	Key properties of PCCT	Advantages in neurology
Neurovascular imaging	High spatial resolution, reduction of blooming artifacts, enhanced visualization of stents and metallic implants	Improved evaluation of tiny intracranial vessels, arterial stenoses, and vascular stents; reduced artifacts near the skull base
Acute ischemic stroke	Superior signal-to-noise ratio, enhanced grey-white matter contrast	Early detection of ischemic changes, differentiation of hemorrhage from contrast media
Spinal CSF leaks and fistulas	Enhanced resolution, virtual monoenergetic imaging	Precise detection of CSF leaks and venous fistulas, reduced radiation exposure
Deep brain stimulation electrode imaging	Ultra-high resolution, reduced noise, clear visualization of segmented contacts	Accurate postoperative assessment of electrode placement and orientation
Middle and internal ear pathologies	Superior in-plane resolution, thinner section thickness	Enhanced visualization of ossicular chains, dislocations, and cochlear implant positioning
Atherosclerotic plaque characterization	Material differentiation through spectral imaging	Improved detection of rupture-prone plaques and assessment of intraplaque hemorrhage and lipid content
Post-treatment monitoring (Aneurysms and stents)	High-resolution imaging, reduced blooming artifacts	Detailed visualization of stent apposition, in-stent stenoses, and aneurysm occlusion devices
Cranial and spinal tumors	Enhanced contrast-to-noise ratio, soft-tissue resolution	Better delineation of tumor margins and detection of smaller lesions

PCCT: Photon-counting computed tomography; CSF: Cerebrospinal fluid.