Photon-counting computed tomography in coronary artery bypass grafting planning and follow-up: a narrative review of a high-resolution adjunct to invasive angiography

Introduction

Coronary artery disease (CAD) remains a leading cause of morbidity and mortality worldwide, and optimal preoperative imaging is central to successful coronary artery bypass grafting (CABG). Surgical planning depends on accurate assessment of stenosis severity, plaque morphology, distal target quality, and the presence of prior stents or complex anatomy. Conventional imaging modalities—including invasive coronary angiography and energy-integrating detector computed tomography (EID-CT)—have advanced perioperative evaluation but remain limited by spatial resolution, artifact burden, and radiation exposure (1-3).

Photon-counting computed tomography (PC-CT) introduces several advances that directly address these limitations. By counting individual photons and measuring their energy, PC-CT achieves markedly higher spatial resolution, improved contrast-to-noise performance, and true spectral imaging. These capabilities enhance visualization of small distal vessels, reduce blooming from calcifications and stents, and enable more accurate plaque characterization than conventional computed tomography (CT). Together, these improvements position PC-CT as a potentially valuable tool for refining CABG planning and postoperative graft assessment. Conventional imaging modalities—including invasive coronary angiography and EID-CT—have advanced perioperative evaluation but remain limited by spatial resolution, artifact burden, and radiation exposure (4,5).

As PC-CT systems enter clinical practice, their potential role in surgical decision-making has become increasingly relevant. Early studies suggest meaningful improvements in stenosis quantification and stent evaluation, with the potential for reduced radiation exposure in standard cardiac PC-CT acquisitions. However, ultrahigh-resolution (UHR) modes used for maximal spatial detail may involve higher doses (1,3,4). Yet widespread adoption is limited by availability, workflow considerations, and the need for broader clinical validation. This review summarizes the technical principles of PC-CT, evaluates current evidence relevant to CABG planning and follow-up, and outlines the challenges and future directions for integrating this emerging modality into surgical practice. We present this article in accordance with the Narrative Review reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-0825/rc).

Methods

We conducted a targeted literature review of studies published between 2018 and 2025 using combinations of the following terms: “photon-counting CT”, “photon-counting detector CT”, “coronary CT angiography”, “coronary artery disease”, “stent evaluation”, “plaque characterization”, “bypass graft imaging”, and “cardiac surgery”. Additional references were identified through manual review of bibliographies from key articles. Search strategy is summarized in Table 1.

Because PC-CT is an emerging technology with limited multicenter data, we included feasibility studies, phantom experiments, technical evaluations, single-center clinical studies, and early postoperative imaging reports. Studies were selected for relevance to CABG planning domains, including stenosis assessment, plaque characterization, stent visualization, distal target evaluation, and graft imaging. Technical papers describing detector design, spectral imaging, and reconstruction approaches were included when they informed clinical applications. This review does not constitute a systematic review or meta-analysis, and no formal quality assessment was performed. A structured summary of the key studies relevant to PC-CT in coronary imaging is provided in Table 2.

Results

Principles of PC-CT

To understand how PC-CT may influence CABG planning, it is essential to first review the technical principles that differentiate it from conventional energy-integrating CT.

Photon-counting detector CT represents a major technological advance in cardiovascular imaging, fundamentally differing from conventional EID-CT. In EID-CT, X-ray photons are converted into visible light within a scintillator and the total energy deposited is integrated by photodiodes. This process, while effective, results in the loss of spectral information, reduced spatial resolution, and increased electronic noise. By contrast, PC-CT directly converts individual photons into electrical signals using semiconductor materials such as cadmium telluride or cadmium zinc telluride, allowing each photon to be counted and its energy measured. This capability enables true spectral imaging and ultrahigh-resolution acquisition, setting the stage for improved diagnostic performance in CAD and cardiothoracic surgery (6,7).

The technical advantages of PC-CT angiography (PC-CTA) are multifaceted. By measuring the energy of individual photons, the system provides spectral imaging that allows material decomposition and tissue differentiation, which is particularly valuable for distinguishing calcified from non-calcified coronary plaque (8). The smaller detector pixel sizes contribute to markedly higher spatial resolution, permitting visualization of fine anatomical structures such as distal coronary branches with unprecedented clarity (7). Furthermore, direct photon counting eliminates electronic noise inherent in EID-CT, resulting in superior contrast-to-noise ratios and more reliable image quality even at lower radiation doses (6). Another important advantage is the reduction of blooming artifacts around calcified plaques and metallic stents, which enhances the accuracy of stenosis quantification (5). Taken together, these features allow PC-CT to deliver comparable or superior diagnostic performance at reduced radiation exposure, a benefit of particular importance for younger patients and those requiring repeated imaging (4).

These technical advances translate directly into improved coronary imaging performance, particularly in the evaluation of CAD, where PC-CT has shown clear diagnostic advantages. Key technical differences between PC-CT and EID-CT are summarized in Table 3.

PC-CTA in CAD

PC-CTA has demonstrated significant promise in the evaluation of CAD. By leveraging ultrahigh spatial resolution and spectral imaging, PC-CTA improves diagnostic accuracy compared with conventional CT angiography, particularly in patients with heavy calcification where blooming artifacts often obscure lumen assessment (9).

This reduction in artifact burden allows for more reliable quantification of stenosis severity, minimizing the risk of overestimating lesion significance and thereby reducing unnecessary interventions (9).

Figure 1 illustrates a representative case of a 70-year-old male with prior CABG [left internal mammary artery (LIMA)-left anterior descending (LAD)] performed a decade earlier who presented with symptomatic severe aortic valve stenosis. During preoperative evaluation, invasive coronary angiography provided only limited visualization of the LIMA graft. PC-CT offered high-resolution assessment of the graft, demonstrating a widely patent LIMA-LAD anastomosis. This non-invasive confirmation of graft patency supported clinical decision-making and allowed the heart team to proceed confidently with transcatheter aortic valve replacement.

Figure 1 Two images showing the left main and LAD artery. (A) PC-CT demonstrating a widely patent LIMA-LAD segment (with a clearly open lumen). (B) Invasive angiography confirming LIMA-LAD patency and showing the same vessels and a patent anastomosis. LAD, left anterior descending; LIMA, left internal mammary artery; PC-CT, photon-counting computed tomography.

Figure 2 illustrates a case of severe proximal and distal RCA stenosis where PC-CTA and invasive angiography demonstrate concordant findings, highlighting the modality’s reliability in delineating high-grade lesions and distal vessel detail.

Figure 2 Two images showing the right coronary artery and a sever stenosis in its proximal and distal runoff. (A) PC-CT image of a severe right coronary artery proximal and distal stenosis. (B) Invasive angiography confirming the severely stenosed right coronary artery. PC-CT, photon-counting computed tomography.

Another major advantage of PC-CTA is its ability to maintain diagnostic image quality at lower radiation doses in standard cardiac acquisition modes. Recent studies have shown that standard PC-CT protocols can reduce radiation exposure compared with contemporary EID-CTA, an important consideration for younger patients and those requiring serial follow-up (10). In contrast, UHR acquisitions—often used for detailed plaque, stent, and distal vessel evaluation—may involve higher doses. The dose characteristics therefore depend on the selected acquisition mode, with improved detector efficiency and reduced electronic noise contributing to lower exposure in standard PC-CT imaging (10).

Beyond stenosis detection, PC-CTA enables advanced plaque characterization. The improved spatial resolution allows for more accurate quantification of plaque burden and morphology, while spectral imaging facilitates differentiation between calcified, fibrous, and lipid-rich components (11). These capabilities support risk stratification by identifying vulnerable plaques that may predispose patients to acute coronary syndromes (4,5). In this way, PC-CTA moves beyond anatomical assessment to provide insights into plaque biology and rupture risk.

Stent imaging is another domain where PC-CT offers clear benefits. Conventional CT often struggles with in-stent visualization due to blooming artifacts and limited resolution. PC-CTA, however, provides improved delineation of stent struts and lumen patency, enabling more accurate detection of in-stent restenosis (12,13). Case reports and phantom studies have validated these findings against optical coherence tomography (OCT), the current gold standard for stent evaluation (12). This suggests that PC-CTA may become a non-invasive alternative for routine stent follow-up in clinical practice.

Taken together, these advances position PC-CTA as a transformative tool in CAD imaging. It not only enhances diagnostic accuracy and patient safety but also expands the scope of CT angiography to include functional and biological insights into coronary pathology.

The same improvements that enhance CAD assessment also have direct implications for surgical planning, especially in patients being evaluated for CABG.

Radiation dose considerations

Radiation exposure with PC-CT is mode-dependent, and this distinction is essential when interpreting its role in CABG planning. Standard cardiac PC-CTA protocols typically achieve diagnostic image quality at lower effective doses than contemporary EID-CTA because of improved detector efficiency and reduced electronic noise. In contrast, UHR acquisitions, which are often required for detailed plaque, stent, and distal target evaluation, may involve higher radiation doses than standard PC-CT modes.

To avoid ambiguity and reflect protocol-dependent variability, Table 4 summarizes representative effective dose ranges for PC-CT (standard and UHR modes), modern EID-CTA, and invasive coronary angiography. These values clarify that “dose efficiency” applies primarily to standard PC-CT acquisitions, whereas UHR imaging represents a deliberate trade-off between spatial resolution and radiation exposure.

Applications in cardiac surgery

PC-CTA is increasingly recognized as a possible transformative modality in the preoperative evaluation of patients undergoing CABG. Its ultrahigh spatial resolution and spectral imaging capabilities allow surgeons to visualize distal coronary branches and small target vessels with unprecedented clarity. This is particularly important in CABG planning, where the choice of graft targets depends on accurate assessment of vessel caliber, distal runoff, and the presence of diffuse disease. Conventional energy-integrating CT often suffers from blooming artifacts around calcified plaques, leading to overestimation of stenosis severity and misclassification of lesion significance. PC-CTA reduces these artifacts, enabling more reliable quantification of stenosis and thereby improving surgical decision-making (1-3).

In patients with prior percutaneous interventions, stent evaluation is central to surgical planning because patency and restenosis determine graft strategy. Conventional CT struggles with in-stent visualization, whereas PC-CTA improves delineation of stent struts and lumen, with findings corroborated against OCT and optimized reconstruction approaches, supporting non-invasive assessment before CABG (12,13). Following stent assessment, UHR cardiac acquisitions can provide enhanced distal target detail, although typically at higher radiation doses than standard PC-CT protocols. When standard cardiac PC-CTA is used for earlier or intermediate evaluations, the lower-dose nature of these modes may help reduce cumulative radiation across multi-stage CABG planning pathways (14). Postoperatively, PC-CT’s combination of high spatial resolution and spectral reconstructions supports longitudinal graft surveillance, enhancing visualization of bypass conduits and distal runoff and potentially reducing reliance on invasive angiography in follow-up pathways (16).

Collectively, PC-CTA integrates anatomical precision for distal targets, reliable stent evaluation, and the potential for lower radiation exposure in standard cardiac acquisition modes into a single modality that strengthens preoperative planning and postoperative monitoring. The result is fewer unnecessary invasive angiograms, more accurate graft target selection, and potentially improved outcomes for patients undergoing CABG as evidence expands across the perioperative continuum (1-3,12-14,16).

The complementary strengths and limitations of PC-CT and invasive coronary angiography for CABG-related coronary assessment are summarized in Table 5.

While these applications highlight the potential of PC-CT in surgical pathways, the strength of the modality ultimately depends on the clinical evidence supporting its use.

Clinical evidence and current studies

PC-CT has progressed from technical feasibility into robust clinical validation. Several prospective and retrospective studies have demonstrated its superiority over conventional energy-integrating CT in CAD assessment, stent evaluation, and CABG planning.

Nakashima et al. (1) showed in a large comparative study that PC-CT significantly reduced false-positive stenosis diagnoses compared with conventional CT, thereby lowering the rate of unnecessary invasive angiography. Mergen et al. (2) emphasized that PC-CT offers both spectral and high-resolution modes, enabling tailored imaging strategies depending on whether plaque characterization or fine anatomical detail is prioritized.

Stent evaluation has been a major limitation of conventional CT. Száraz et al. (12) reported an OCT-validated case where PC-CT provided UHR visualization of severe in-stent restenosis, with lumen and stent measurements closely matching invasive OCT. Michael et al. (13) demonstrated in phantom experiments that optimized reconstruction kernels in PC-CT improved imaging of in-stent stenoses, reducing the proportion of non-assessable stents.

Beyond preoperative planning, Flohr et al. (14) described dose-efficient UHR cardiac acquisitions that preserve distal target detail at lower exposure, directly benefiting CABG target selection and reducing cumulative radiation in multi-stage evaluations. Cademartiri et al. (16) reviewed current and future cardiovascular applications, highlighting PC-CT’s role in postoperative graft surveillance, where its spectral reconstructions enhance visualization of bypass conduits and distal runoff, potentially reducing reliance on invasive angiography.

Together, these studies establish a growing body of evidence: PC-CT improves diagnostic accuracy in CAD, enhances stent visualization, reduces unnecessary invasive angiography, and shows promise for graft patency follow-up. While larger multicenter trials are still needed, current data strongly support its integration into routine CABG planning and postoperative care.

Despite encouraging results across multiple domains, several practical and technical barriers currently limit widespread adoption of PC-CT in routine cardiac surgery workflows.

Challenges and limitations

Despite its promise, PC-CT faces several challenges that currently limit widespread adoption in routine cardiac surgery planning. One of the most pressing issues is availability and cost. PC-CT scanners remain expensive and are only installed in select academic centers, restricting access for broader patient populations. This limited distribution also slows the accumulation of large multicenter datasets, which are essential for validating outcomes in diverse clinical settings (6,7).

Another limitation is workflow integration. While PC-CT offers ultrahigh resolution and spectral imaging, these capabilities generate large datasets that require advanced reconstruction algorithms and significant computational resources. Imaging departments must adapt to new post-processing pipelines, and clinicians need training to interpret spectral plaque characterization and novel image biomarkers. Without standardized protocols, variability in acquisition and reconstruction may undermine reproducibility across institutions (6,8).

Radiation dose remains a nuanced challenge. Although PC-CT can achieve dose-efficient imaging, UHR acquisitions may increase exposure if not carefully optimized. Balancing diagnostic detail with patient safety requires strict adherence to protocol design and dose-modulation strategies (10,14). Similarly, contrast use is a limitation: spectral imaging often demands optimized contrast timing and volume, which may be problematic in patients with renal impairment.

Technical artifacts also persist. While PC-CT reduces blooming around calcified plaques, motion artifacts from high heart rates or arrhythmias remain problematic. Studies have shown that temporal resolution, though improved, is still inferior to invasive angiography for dynamic coronary flow assessment (4).

Figure 3 demonstrates this limitation in a left main lesion where PC-CT provided improved plaque delineation but modestly overestimated stenosis severity compared with invasive angiography. This highlights the need for cautious interpretation.

Figure 3 Three images of the left main coronary artery. (A) Two images of PC-CT showing calcified plaque in the left main coronary artery with apparent narrowing. (B) Invasive angiography demonstrating less severe stenosis than suggested by PC-CT, indicating modest overestimation in this calcified LM segment. LM, left main; PC-CT, photon-counting computed tomography.

In addition, stent visualization, though markedly better than conventional CT, is not flawless; very small stents or overlapping metallic structures can still obscure lumen evaluation (12,13).

Finally, evidence gaps remain. Most published studies are single-center or involve relatively small cohorts. Large randomized trials comparing PC-CT directly with invasive angiography for CABG planning are lacking. Longitudinal data on graft patency surveillance are also preliminary, with only early feasibility reports available (16). Until these evidence gaps are addressed, PC-CT will remain an adjunct rather than a full replacement for invasive angiography in surgical planning.

Addressing these limitations will require coordinated technological, clinical, and operational progress, several aspects of which are already emerging.

Future directions

PC-CT is poised to reshape cardiovascular imaging and CABG planning, but several avenues of development remain critical for its full clinical integration. One major direction is the expansion of multicenter trials. Current evidence is largely derived from single-center studies or small cohorts, which limits generalizability. Ongoing collaborative efforts are beginning to validate PC-CT against invasive angiography across diverse patient populations, with endpoints including diagnostic accuracy, graft patency, and long-term outcomes (17).

Another promising frontier is postoperative graft surveillance. CT angiography has already been evaluated as a non-invasive alternative for graft patency assessment after CABG, with meta-analyses showing encouraging diagnostic performance compared with invasive angiography (18). PC-CT, with its superior resolution and spectral capabilities, is expected to further improve graft visualization and long-term monitoring, but larger dedicated studies are needed.

Technological innovation will also drive future applications. Advances in detector design and integration with artificial intelligence (AI) are being actively explored. AI-based reconstruction and material decomposition algorithms can enhance image quality, reduce noise, and automate plaque characterization, potentially streamlining workflows and reducing inter-observer variability (19). These developments will be essential for translating PC-CT into everyday clinical practice.

Finally, health-economic evaluations are needed. Cost-effectiveness analyses presented in recent cardiovascular imaging studies suggest that UHR PC-CT could reduce unnecessary invasive angiography and downstream testing, resulting in substantial healthcare savings (15). Demonstrating economic value will be crucial for broader adoption in high-volume cardiac centers.

In summary, future directions for PC-CT in CABG planning include multicenter validation, postoperative graft surveillance, technological innovation, and health-economic assessment. Together, these pathways will determine whether PC-CT transitions from a promising innovation to a standard of care in cardiac surgery.

Discussion

PC-CT provides a level of anatomic detail that directly supports contemporary CABG planning, particularly in patients with diffuse calcification, prior stents, or small distal targets. Its ultrahigh spatial resolution, reduced blooming, and spectral capabilities address several long-standing limitations of conventional CT and offer a non-invasive pathway to more reliable target selection and postoperative graft assessment. Early clinical studies consistently demonstrate improved visualization of distal vessels, more accurate stenosis quantification, and enhanced evaluation of stented segments, with expanding feasibility data in graft imaging. The clinical implications of these imaging advantages across common CABG scenarios are summarized in Table 6.

Despite these advantages, integration into routine surgical practice has been gradual. CABG workflows have historically centered on invasive angiography, a modality deeply embedded in preoperative evaluation and institutional pathways. Transitioning away from this established standard requires not only technical superiority but also operational compatibility with surgical planning. Adoption is further influenced by variable exposure to advanced CT techniques during training and by the availability of photon-counting systems and post-processing resources across institutions. These factors contribute to a slower uptake even when the imaging capabilities are clinically relevant.

Conclusions

PC-CT offers substantially improved coronary visualization through ultrahigh spatial resolution, reduced blooming, and spectral imaging capabilities. These advances enhance stenosis assessment, stent evaluation, distal target selection, and early graft imaging, supporting more informed surgical planning. As multicenter validation expands and standardized protocols mature, PC-CT is poised to assume a more central role in CABG evaluation. Invasive angiography may increasingly serve as a selective rather than routine diagnostic tool when non-invasive imaging remains inconclusive.

Acknowledgments

The authors thank the staff of Houston Methodist DeBakey Heart & Vascular Center for their support during manuscript preparation.

Footnote

Reporting Checklist: The authors have completed the Narrative Review reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-0825/rc

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-0825/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-0825/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This article includes only fully de-identified clinical information and imaging. All patient identifiers were removed, and no individual can be identified from the text or accompanying images. Therefore, written informed consent for publication was not required.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Nakashima M, Miyoshi T, Hara S, et al. Photon-Counting CT Enhances Diagnostic Accuracy in Stable Coronary Artery Disease: A Comparative Study with Conventional CT. J Clin Med 2025;14:6049. [Crossref] [PubMed]
2. Mergen V, Eberhard M, Alkadhi H. Coronary angiography with photon-counting detector CT-new options and some critical decisions. Br J Radiol 2025;98:1847-9. [Crossref] [PubMed]
3. Kiani I, Mohebbi A, Jannatdoust P, et al. Comparison of photon-counting CT angiography with energy-integrating CT angiography in coronary artery stenosis: a systematic review and meta-analysis. BMC Med Imaging 2025;25:496. [Crossref] [PubMed]
4. Hagar MT, Soschynski M, Saffar R, et al. Accuracy of Ultrahigh-Resolution Photon-counting CT for Detecting Coronary Artery Disease in a High-Risk Population. Radiology 2023;307:e223305. [Crossref] [PubMed]
5. Wolf EV, Halfmann MC, Varga-Szemes A, et al. Photon-Counting Detector CT Virtual Monoenergetic Images for Coronary Artery Stenosis Quantification: Phantom and In Vivo Evaluation. AJR Am J Roentgenol 2024;222:e2330481. [Crossref] [PubMed]
6. Willemink MJ, Persson M, Pourmorteza A, et al. Photon-counting CT: Technical Principles and Clinical Prospects. Radiology 2018;289:293-312. [Crossref] [PubMed]
7. Rajendran K, Petersilka M, Henning A, et al. First Clinical Photon-counting Detector CT System: Technical Evaluation. Radiology 2022;303:130-8. [Crossref] [PubMed]
8. Flohr T, Petersilka M, Henning A, et al. Photon-counting CT review. Phys Med 2020;79:126-36. [Crossref] [PubMed]
9. Halfmann MC, Bockius S, Emrich T, et al. Ultrahigh-Spatial-Resolution Photon-counting Detector CT Angiography of Coronary Artery Disease for Stenosis Assessment. Radiology 2024;310:e231956. [Crossref] [PubMed]
10. Araki S, Nakamura S, Takafuji M, et al. Ultra-low-dose coronary computed tomography angiography using photon-counting detector computed tomography. Eur Heart J Imaging Methods Pract 2024;2:qyae125. [Crossref] [PubMed]
11. Rajagopal JR, Farhadi F, Richards T, et al. Evaluation of Coronary Plaques and Stents with Conventional and Photon-counting CT: Benefits of High-Resolution Photon-counting CT. Radiol Cardiothorac Imaging 2021;3:e210102. [Crossref] [PubMed]
12. Száraz L, Kulyassa P, Maurovich-Horvat P, et al. Photon-counting CT for coronary stent evaluation: OCT-validated case of severe in-stent restenosis. Int J Cardiovasc Imaging 2025;41:1845-6. [Crossref] [PubMed]
13. Michael AE, Schoenbeck D, Becker-Assmann J, et al. Coronary stent imaging in photon counting computed tomography: improved imaging of in-stent stenoses in a phantom with optimized reconstruction kernels. BJR Open 2024;6:tzae030. [Crossref] [PubMed]
14. Flohr T, Schmidt B, Ulzheimer S, et al. Cardiac imaging with photon counting CT. Br J Radiol 2023;96:20230407. [Crossref] [PubMed]
15. Kataria V, Yaduvanshi I, Singal G, et al. Establishing a diagnostic reference level of radiation dose in coronary angiography and intervention: A prospective evaluation. Indian Heart J 2021;73:725-8. [Crossref] [PubMed]
16. Cademartiri F, Maffei E, Cau R, et al. Current and future applications of photon-counting computed tomography in cardiovascular medicine. Heart 2025;111:1109-18. [Crossref] [PubMed]
17. Mantaj P, Hirofuji A, Dell'Aquila M, et al. Meta-Analysis of Coronary Bypass Graft Patency Assessment With Invasive vs Computed Tomographic Angiography. Ann Thorac Surg 2025;120:1016-27. [Crossref] [PubMed]
18. Deng A, Day J, Guliyev E, et al. Artificial intelligence for X-ray photon counting technology: current status and future perspectives. In: Iniewski KK, Cai LK, editors. Deep Learning for Advanced X-ray Detection and Imaging Applications. Cham: Springer; 2024:229-57.
19. Vecsey-Nagy M, Emrich T, Tremamunno G, et al. Cost-effectiveness of ultrahigh-resolution photon-counting detector coronary CT angiography for the evaluation of stable chest pain. J Cardiovasc Comput Tomogr 2025;19:106-12. [Crossref] [PubMed]